Patent Application
20240194895
The rapid climate deterioration due to CO2 emission and fossil fuel consumption has manifested the significance of technology developing for hydrogen that is an energy carrier with high energy density for versatile energy conversion with the minimum environmental impact. Solid oxide cells (SOCs) that can be powered by pure H2 for electricity generation in the fuel cell mode and can work reversibly as an electrolyzer for H2 production possess the unrivaled highest energy conversion efficiencies among all the competing technologies (Ref. 1). However, for stationary electricity generation with a long-term of 3-5 years, the current state-of-the-art solid oxide fuel cells (SOFCs) continuously face electrode degradation challenges. Developing more robust electrodes are still the top priority for SOCs development. In terms of the oxygen electrode, the current state-of-the-art high-performance electrode commonly employs a cobaltite-based perovskite, including lanthanum strontium cobalt ferrite (LSCF; Ref. 2). LSCF has a high ionic and electrical conductivity, high oxygen self-diffusion coefficient, and oxygen surface exchange coefficient. As an effective electrocatalyst, LSCF cathodes have active areas for oxygen reduction reaction across the entire surface.
Nevertheless, LSCF cathode presents inadequate long-term durability due to intrinsic materials degradation of Sr segregation (Refs. 3-8). For the SOFC stacks, electrode degradation caused by Sr surface segregation is further accelerated due to their interaction with the volatile Cr species that are evaporated from the Cr-containing interconnects. Although various solution-based infiltration has been developed to decorate the internal surface of the porous oxygen-electrode (Refs. 9-10) its impact on enhancing the stability of the LSCF appears to be limited partially due to the discrete nature of the infiltrated materials with uncontrolled microstructure. To effectively mitigate the Sr surface segregation and Cr contamination, it is essential to have a conformal surface coating layer inert to both Sr and Cr and serving as the barrier for Sr outward diffusion and Cr inward diffusion. On the other aspect, completely sealing off the LSCF/SDC backbone surface leads to the loss of cathode electroactivity. So, such a coating layer must be capable of carrying sufficient electrocatalytic activity for the oxygen reduction reaction (ORR). Plus, this coating layer needs to possess sufficiently high ionic conductivity to facilitate subsequent mass transfer for the dissociated oxygen ions.
Other than the aforementioned strict requirement in terms of the chemistry, conformity, and electrochemical properties, the coating layer also needs to be applied to the internal surface of the porous electrode that possesses complex topography with a high aspect ratio. Furthermore, the nanostructured materials are thermally sensitive at a modest temperature of ˜400° C. (Refs. 11-12) because of the large surface-to-volume ratio and high surface energy of nanocrystals. Accordingly, there is an enormous concern about the structural stability of nanocrystals in the coating layer at elevated temperatures for the desired lifetime. Therefore, developing a conformal coating to mitigate the Sr surface segregation in SOFCs, while maintaining the electrode's functionality is incredibly sophisticated.
Despite advances in solid oxide fuel cells (SOFCs) research, there is still a scarcity of materials and fabrication methods to address current issues and constraints around electrode degradation. These needs and other needs are satisfied by the present disclosure.
In accordance with the purpose(s) of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to ALD-coated cells comprising a conformal ultra-thin nanocomposite comprising Pt and CoOx on a LSCF/SDC cathode backbone. In a further aspect, the ALD-coated cells comprising an ultra-thin nanocomposite comprising Pt and CoOx on a LSCF/SDC cathode backbone are prepared using a disclosed Atomic Layer Deposition (ALD) coating method. In a still further aspect, the disclosed ALD-coated cells comprise a heterogeneous coating layer comprising subjacent discrete Pt nanoparticles capped with superjacent fully dense conformal CoOx layer. In a yet further aspect, the performance of the disclosed ALD-coated cells is improved compared to baseline cells lacking the disclosed ALD coating on a LSCF/SDC cathod backbone.
Disclosed herein are coated electrodes comprising: an electrode comprising a nanocomposite coating; wherein the nanocomposite coating comprises: a layered coating comprising: a first coating layer; and a second coating layer; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeyOx; doped CeyOx; LayNizOx; doped LayNizOx; or combinations thereof; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer.
Also disclosed herein nanocomposite coatings comprising: a layered coating comprising: a first coating layer; and a second coating layer; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeyOx; doped CeyOx; LayNizOx; doped LayNizOx; or combinations thereof; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer.
Also disclosed herein are electrodes comprising a disclosed nanocomposite coating on at least one surface of the electrode.
Also disclosed herein are products comprising a disclosed electrode.
Also disclosed herein are solid oxide cells comprising a disclosed electrode.
Also disclosed herein are heterogenous nanocomposite coatings comprising; at least two layers, wherein one layer of the coating is a subjacent discrete Pt nanoparticles layer and a second layer of the coating is a layer that caps the Pt nanoparticles layer with a superjacent CoOx layer.
Also disclosed are articles comprising a substrate with a disclosed nanocomposite coating on at least one surface of the substrate.
Also disclosed are products comprising a disclosed article.
Also disclosed are methods of making a disclosed coated electrode, the method comprising: providing an electrode in an atomic layer deposition reaction chamber; performing at least one atomic layer deposition cycle to form a first coating layer on a surface of the substrate; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; performing at least one atomic layer deposition cycle to form a second coating layer on the first coating layer; wherein the second coating layer comprises metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeOx; doped CeOx; LayNizOx; doped LayNizOx; or combinations thereof; and wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins on the first coating layer; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer; wherein the first coating layer is superjacent to the substrate.
Also disclosed are methods of providing a disclosed nanocomposite coating on a substrate, the method comprising: providing a substrate an atomic layer deposition reaction chamber; performing at least one atomic layer deposition cycle to form a first coating layer on a surface of the substrate; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; performing at least one atomic layer deposition cycle to form a second coating layer on the first coating layer; wherein the second coating layer comprises metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeOx; doped CeOx; LayNizOx; doped LayNizOx; or combinations thereof; and wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins on the first coating layer; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer; wherein the first coating layer is superjacent to the substrate.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Additional advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description or can be learned by practice of the disclosure. The advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.
Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.
Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.
Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.
While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.
It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.
Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.
As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an ALD-coated cell,” “a nanocomposite,” or “a nanoparticle,” includes, but is not limited to, two or more such ALD-coated cells, nanocomposites, or nanoparticles, and the like.
It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.
When a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y′, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y′, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.
It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.
As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.
As used herein, the term “effective amount” refers to an amount that is sufficient to achieve the desired modification of a physical property of the composition or material. For example, an “effective amount” of a nanocomposite layer refers to a nanocomposite layer that is sufficiently thick to achieve the desired improvement in the property modulated by the nanocomposite layer, e.g., conductivity and/or stability of the cell. The specific level in terms of thickness (nm) required as an effective amount will depend upon a variety of factors composition of the cathode, temperature parameters for use, and the like.
As used herein, “LSCF” refers to a mixed conductor material that comprises lanthanum strontium cobalt ferrite composite oxide. Electrodes, e.g., a cathode, as disclosed herein can comprise LSCF. The LSCF can have the following formula:
La1-mSrmConFe1-nO3-δ,
where n is in the range of 0.4≤n≤0.6 In the foregoing formula, m can be in the range of 0≤m≤0.5, or in particular aspects, about 0.4. In the foregoing, δ oxygen deficiency and δ can vary in the range of 0 or more and 0.5 or less depending on the mole ratio of Sr (that is, m), the mole ratio of Co (that is, n), and the oxidation numbers of Co and Fe. The the ratio of the number of moles of Co to the sum of the number of moles of Co and the number of moles of Fe can be 0.4 or more and 0.6 or less. In some instances, the lanthanum strontium cobalt ferrite composite oxide has the following formula: La0.6Sr0.4Fe0.8Co0.2O3.
As used herein, “LSM” refers to a mixed conductor material that comprises lanthanum strontium manganite composite oxide. Electrodes, e.g., a cathode, as disclosed herein can comprise LSM. The LSM can have the following formula:
La1-mSrmMnnO3±δ.
In some instances, the foregoing formula has the particular formulation of: La1-mSrmMnO3. In other instances, the foregoing formula has the particular formulation of: La0.8Sr0.2MnO3.
As used herein, “[100] direction of LSCF” refers to the [100] crystal orientation of the LSCF that has a rhombohedral crystal structure.
As used herein, “metal oxide nanograins” refers to any grain of material comprising a metal oxide composition having an average grain size on the scale of nanometers, and in various respects, having a diameter less than 1000 nm or less than 100 nm. In various respects, “nanograin” refers to materials and structures sized between about 1 nm to about 1000 nm in at least one dimension, e.g., diameter. Typically the term “nanograin” is used to describe the microstructure of a final densified body made from nanocrystalline metal powders via the described methods, e.g., atomic layer deposition. Nanograin is a crystallite of nanoscale size, which is a building block for polycrystalline material. Nanograin is a monocrystalline element (building block) of a polycrystalline structure, connected with the other nanograins through the grain boundaries (heterojunctions and homojunctions).
As used herein, “solid oxide fuel cell” or “SOFC” refers to an electrochemical conversion device that produces electricity by oxidizing a fuel. Generally speaking, an SOFC operates as follows: reduction of oxygen molecules into oxygen ions occurs at a cathode; an electrolyte material conducts the negative oxygen ions from the cathode to an anode, where electrochemical oxidation of oxygen ions with hydrogen or carbon monoxide occurs; the electrons then flow through an external circuit and re-enter the cathode.
As used herein, “electrode” includes electric conducting structures (including cathode and/or anode) suitable for electrochemical energy conversion devices, including solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) as well as a protonic conductor.
As used herein, “conformal coating” refers to a coating or layer which matches or follows the topography of the underlying substrate.
As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.
Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e., one atmosphere).
The following abbreviations are used herein throughout and can be used interchangeably with the corresponding text phrase.
In one aspect, the present disclosure pertains to coated electrodes. In a further aspect, the coated electrodes comprise: an electrode comprising a nanocomposite coating; wherein the nanocomposite coating comprises: a layered coating comprising: a first coating layer; and a second coating layer; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeyOx; doped CeyOx; LayNizOx; doped LayNizOx; or combinations thereof; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer.
Also disclosed herein nanocomposite coatings, e.g., the nanocomposite coatings provided to an electrode, the nanocomposite coatings comprising: a layered coating comprising: a first coating layer; and a second coating layer; wherein the first coating layer comprises discrete nanoparticles; wherein the discrete nanoparticles comprise Pt, Ag, Au, or combinations thereof; wherein the second coating layer forms a continuous conformal layer comprising metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeyOx; doped CeyOx; LayNizOx; doped LayNizOx; or combinations thereof; wherein the first coating layer is subjacent to the second coating layer; and wherein the second coating layer is superjacent to the first coating layer, thereby capping the first coating layer.
As discussed above in the Background section, high resistance of the oxygen electrode still significantly hinders the state-of-the-art solid oxide fuel cells (SOFCs). For an oxygen electrode comprising mixed electrical and ionic conductors such as perovskite lanthanum strontium cobalt ferrite (LSCF), conventional oxygen electrodes deteriorate due to its low chemical stability and cation surface segregation. The disclosed ALD-coated cells prevent the cation surface segregation and its resultant perovskite phase decomposition. As disclosed herein, the disclosed ALD coating can provide a conformal ultra-thin (5-20 nm) surface heterogeneous coating layer comprising subjacent discrete Pt nanoparticles capped with a superjacent fully dense conformal CoOx layer. Data obtained in the performance studies in the Examples herein below indicate that the disclosed ALD coating reduces the cell series resistance by up to 40%. The disclosed ALD coating layer possesses extraordinary nanostructure stability, presenting an intact morphology comparable to the initial as-deposited state even after operation up to 816 h. The ALD coating comprises a conformal CoOx layer comprising randomly orientated single-layered nanograins, with high-density intergranular and surface grain boundaries serving as the electrochemical reaction sites and facilitating mass transport. The disclosed ALD coating layer suppresses the Sr outward diffusion and confined the Sr-enriched layer to a ˜2 nm interface perovskite phase between the coating layer and the LSCF grain surface. Moreover, this ultra-thin Sr-enriched perovskite layer possesses high oxygen vacancy and high ionic conductivity. It also imposes tensile strain to the LSCF grain surfaces. The disclosed ALD coating layer is estimated to have a conductivity of ˜1.27×104 S/cm, which is greater than two orders magnitude improvement to uncoated LSCF.
In a further aspect, the nanocomposite coating is conformal with the underlying electrode surface and the layered coating of the coating has a nanometer scale thickness. In a further aspect, the layered coated has a total thickness of from about 1 nm to about 200 nm; a total thickness of from about 1 nm to about 100 nm; a total thickness of from about 1 nm to about 80 nm; a total thickness of from about 1 nm to about 60 nm; a total thickness of from about 1 nm to about 40 nm; a total thickness of from about 1 nm to about 20 nm; a total thickness of from about 2 nm to about 100 nm; a total thickness of from about 2 nm to about 80 nm; a total thickness of from about 2 nm to about 60 nm; a total thickness of from about 2 nm to about 40 nm; a total thickness of from about 2 nm to about 20 nm; a total thickness of from about 2 nm to about 15 nm; a total thickness of from about 2 nm to about 10 nm; a total thickness of from about 5 nm to about 15 nm; or a total thickness of from about 5 nm to about 20 nm.
In a further aspect, the layered coating comprises a subjacent discrete nano-metal capped with a superjacent conformal layer, e.g., such that the subjacent discrete layer comprises nano-Pt, nano-Ag, nano-Au, or combinations thereof and the superjacent conformal layer comprises metal oxide nanograins; wherein the metal oxide nanograins comprise CoyOx; doped CoyOx; PryOx; doped PryOx; CeyOx; doped CeyOx; LayNizOx; doped LayNizOx; or combinations.
In a further aspect, the electrode can be a suitable electrode, e.g., a cathode, as used in various types of SOCs. In a still further aspect, the electrode can comprise lanthanum strontium cobalt ferrite (LSCF). In a yet further aspect, the electrode can comprise a LSCF/SDC composite electrode.
In a further aspect, the coated electrode, e.g., a LSCF/SDC composite electrode, when used in an SOC cell series can reduce cell series resistance by at least 5%, by at least 10%, by at least 15%, by at least 20%, by at least 25%, by at least 30%, by at least 35%, by at least 40%, or a range comprising as lower and upper bounds any two values from the foregoing list, or a set of values from the foregoing list. The reduction in the foregoing is a comparative measurement comparing the resistance of SOC series resistance comprising an SOC comprising a disclosed coated electrode compared to substantially the same SOC comprising an uncoated electrode of the same type as the coated electrode but lacking the disclosed coating.
In a further aspect, a cell comprising the a coated exhibits substantially intact morphology of the coating layer after 100 h of operation, after 150 h of operation, after 200 h of operation, after 250 h of operation, after 300 h of operation, after 350 h of operation, after 400 h of operation, after 450 h of operation, after 500 h of operation, after 550 h of operation, after 600 h of operation, after 650 h of operation, after 700 h of operation, after 750 h of operation, after 800 h of operation, or a range comprising as lower and upper bounds any two values from the foregoing list, or a set of values from the foregoing list.
In a further aspect, the superjacent oxide layer, e.g., CoOx, comprises randomly orientated but single-layered nanograins, with high-density intergranular and surface grain boundaries serving as the electrochemical reaction sites and facilitating mass transport.
The disclosed coated electrode transforms an electrode—compared to an uncoated electrode—from an original perovskite surface that is vulnerable to cation segregation and degradation into the disclosed coated electrode comprising an embedded strained interface phase with enormous conductivity. Without wishing to be bound by a particular theory, the coating layer is believed to suppress Sr outward diffusion. Data discussed herein below shows that the coating layer confines a 2 nm Sr-enriched interface layer between the coating layer and the LSCF backbone. The conductivity of the coating layer is estimated to be about 1.27×104 S/cm and two orders magnitude higher than that of LSCF.
The methods disclosed herein can be used to provide the disclosed nanocomposite coating to electrodes of solid oxide cells, including both solid oxide fuel cells (for electricity generation) and solid oxide electrolysis cells (for hydrogen or oxygen production).
In one aspect, the disclosure relates to SOC cells comprising the disclosed coated electrodes, e.g., electrodes comprising a conformal ultra-thin nanocomposite comprising Pt and CoOx on a LSCF/SDC cathode backbone. In a further aspect, the SOC cells comprising the disclosed coated electrodes, e.g., an ultra-thin nanocomposite comprising Pt and CoOx on a LSCF/SDC cathode backbone, are prepared using a disclosed Atomic Layer Deposition (ALD) coating method as disclosed herein. In a still further aspect, the disclosed SOC cells comprise an electrode having a heterogeneous coating layer comprising subjacent discrete Pt nanoparticles capped with superjacent fully dense conformal CoOx layer. In a yet further aspect, the performance of the disclosed ALD-coated cells is improved compared to baseline cells lacking the disclosed ALD coating on a LSCF/SDC cathod backbone.
In one aspect, the disclosure relates to a method of forming a multi-layer electrocatalyst nanostructure on an electrode using atomic layer deposition (ALD). More specifically, in one aspect, the disclosed method includes using ALD to deposit a first layer comprising a plurality of discrete nanoparticles of a first electrocatalyst on a surface of the electrode, and depositing one or more of a second layer comprising a second electrocatalyst superjacent the electrode and the first layer.
Generally speaking, atomic layer deposition is a subclass of chemical vapor deposition and encompasses a thin-film deposition technique based on the sequential use of a gas phase chemical process. During atomic layer deposition a film is grown on a substrate by exposing its surface to alternate gaseous species, typically referred to as precursors. The precursor molecules react with the surface in a self-limiting way, so that the reaction terminates once all the reactive sites on the surface are consumed. Consequently, the maximum amount of material deposited on the surface after a single exposure to all of the precursors (a so-called ALD cycle) is determined by the nature of the precursor-surface interaction. By varying the number of cycles it is possible to grow materials uniformly and with high precision on arbitrarily complex and large substrates. Through the repeated exposure to separate precursors, a thin film is slowly deposited on a target surface. The chemistry of any particular layer can be specified or modified by selecting the precursors, the oxidant, the processing temperature, the processing pressure, or a combination thereof, each of which can be automated and controlled with a control system. ALD is considered one deposition method with great potential for producing very thin, conformal films with control of the thickness and composition of the films possible at the atomic level.
According to various aspects, the ALD technique comprises introducing a precursor and an oxidant to the subjacent layer or surface and allowing the precursor to react with the subjacent layer or surface, forming a thin film layer thereon. The precursor can be selected from any suitable precursor that will provide the desired layer by ALD. Exemplary precursors include, for example: Cerium(III) trifluoroacetylacetonate hydrate; Tris(cyclopentadienyl)cerium(III); Tris(i-propylcyclopentadienyl)cerium(III); Bis(N-t-butyl-N′-ethylpropanimidamidato)cobalt(II); Bis(N,N′-di-i-propylacetamidinato)cobalt(II); Bis(1,4-di-t-butyl-1,3-diazabutadienyl)cobalt(II) Co(DAD)2; Bis(cyclopentadienyl)cobalt(II); Bis(N,N′-di-i-propylacetamidinato)cobalt(II); Tris(cyclopentadienyl)lanthanum; Tris(N, N′-di-i-propylformamidinato)lanthanum(III); Tris(i-propylcyclopentadienyl)lanthanum; Bis(ethylcyclopentadienyl)nickel; Bis(cyclopentadienyl)nickel; Bis(pentamethylcyclopentadienyl)nickel; Bis(i-propylcyclopentadienyl)nickel; Platinum(II) acetylacetonate; Platinum(II) hexafluoroacetylacetonate; (Trimethyl)cyclopentadienylplatinum(IV); (Trimethyl)methylcyclopentadienylplatinum(IV); Praseodymium(III) hexafluoroacetylacetonate; Tris(cyclopentadienyl)praseodymium; or Tris(i-propylcyclopentadienyl)praseodymium. The oxidant can be selected from any suitable oxidant that will provide the desired electrocatalyst layer. Exemplary oxidants include hydrogen peroxide (H2O2), Water (H2O), Oxygen (O2) and Ozone (O3).
In one aspect, the disclosed method involves depositing a first layer of Pt catalyst on a target surface of an electrode, wherein the first layer of Pt catalyst comprises a plurality of particles (or grains) having a first particle (or grain) size. The method further comprises depositing one or more of a second layer of a second electrocatalyst superjacent the first Pt layer and the surface of the electrode, to provide one or more second layers having second thickness. In various aspects, the target surface of the electrode may be an internal surface, an external surface, or both. In various aspects, the first layer can provide coverage of the substrate area to the extent of about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or range of substrate area coverage with an lower and upper limit comprising any of the foregoing values, or a set of values selected from any of the foregoing values. In some aspects, the first layer coverage can be any amount such that a nano-grained network is formed with grain boundaries acting as pathway for oxygen diffusion. There may be some advantage to higher levels of substrate coverage, but this would be balanced against cost (greater amounts of catalyst in the first layer utilized) and benefit (whether the increase in performance were justified by the layer costs) considerations.
References are cited herein throughout using the format of reference number(s) enclosed by parentheses corresponding to one or more of the following numbered references. For example, citation of references numbers 1 and 2 immediately herein below would be indicated in the disclosure as (Refs. 1-2).
The following listing of exemplary aspects supports and is supported by the disclosure provided herein.
From the foregoing, it will be seen that aspects herein are well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.
While specific elements and steps are discussed in connection to one another, it is understood that any element and/or steps provided herein is contemplated as being combinable with any other elements and/or steps regardless of explicit provision of the same while still being within the scope provided herein.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.
Since many possible aspects may be made without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings and detailed description is to be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.
Now having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.
Commercially available, anode-supported solid oxide button cells fabricated by Materials and Systems Research, Inc. (MSRI, Salt Lake City, UT) were employed for all the experiments described in this paper. MSRI cells were composed of five layers as follows: starting from the anode: (a) a ˜700 μm thick Ni/YSZ cermet layer which supports the cell structure; (b) a ˜10 μm thick Ni/YSZ active layer; a ˜10 μm thick YSZ electrolyte; (c) a thin (2-3 μm) dense Sm2O3-doped CeO2 (SDC) barrier layer, (d) a ˜10 μm thick La0.6Sr0.4CO0.2Fe0.8O3-δ (LSCF)/SDC active layer; and (e) a 50 μm thick, pure LSCF current collecting layer. The active area (limited by the cathode) of the cell is 2 cm2. The exposure area of the anode to fuel was about 3.5 cm2.
The ALD coatings were performed in a commercial GEMStar-8 ALD reactor from Arradiance Inc. The precursors used in this study were all purchased from Strem Chemicals, Inc. The (trimethyl)methylcyclopentadienylplatinum(IV)/(99%) and the deionized water were used as Pt precursor and oxidant for depositing the Pt layer; and the bis(cyclopentadienyl)cobalt (II), (min. 98% cobaltocene) and ozone were used as Co and oxidant, respectively, for CoOx layer growth. During the deposition, the (trimethyl)methylcyclopentadienylplatinum and bis(cyclopentadienyl)cobalt containers were maintained at 75° C. and 90° C., respectively; and the reactor chamber was set at 300° C. Desired cycles were performed for Pt and CoOx deposition, respectively, leading to a dual-layer ALD coating of Pt first, followed by Co3O4 (120 cycles for both cells) on each cell cathode backbone. The Pt layer thickness (Pt loading level) was different for each of the exemplary ALD-coated cells, i.e., Cell #2 was processed 30 cycles and Cell #4 was processed 60 cycles and had a loading of Pt twice as Cell #2. The baseline cells (Cell #1 and 3) and exemplary ALD-coated cells (Cell #2 and 4) used in these Examples herein below are summarized in Table 1 below. No masking or specific treatment was applied on the NiO/YSZ anode before ALD processing. Without wishing to be bound by a particular theory, it is believed that the thick and very dense NiO/YSZ anode prevents precursor penetration during the ALD processing, and the impact of ALD coating on the Ni/YSZ anode is negligible. No surface pretreatment or heat-treatment was applied before or after ALD coating. The cell electrochemical operation was carried out directly after the ALD coating.
One baseline, Cell #1, and ALD-coated, Cell #2, were subjected to operation at 750° C., and another baseline, Cell #3, and another ALD-coated, Cell #4, were examined at 650° C. All cell tests were performed on a test stand. The platinum mesh was used for anode and cathode lead connections. The fuel and air stream flow rates were controlled separately using mass flow controllers. During the operation, a 400 mL/min air flow rate and a 400 mL/min fuel flow rate were used. Before any electrochemical measurements, both cells were current-treated for approximately ˜15 h under a small current density of 0.1 A/cm2 to ensure they were activated. After that, the samples were loaded at a constant current of 0.3 A/cm2 for desired periods. The cell performance was examined using a TrueData-Load Modular Electronic DC Load, which guarantees voltage and current accuracies of 0.03% FS of the range selected +/−0.05% of the value. The cell impedance spectra were examined using a potentiostat/galvanostat (Solartron 1287A) equipped with a frequency response analyzer (Solartron 1260). Impedance measurements were carried out using a Solatron 1260 frequency response analyzer in a frequency range from 50 mHz to 100 KHz. The impedance spectra and resistance (ohmic resistance Rs and polarization resistance Rp) presented are those measured under a DC bias current of 0.3 A/cm2. On a Nyquist plot, Rs was determined by the intercept at the higher frequency end, and Rp was determined by the distance between two intercepts.
After the electrochemical operation, the ALD-coated cells were sectioned and subjected to nanostructural and crystallographic examination using high resolution (HR) Transmission Electron Microscopy (TEM). TEM samples were prepared by mechanical polishing and ion milling in a liquid-nitrogen-cooled holder. Electron diffraction, diffraction contrast, and HRTEM imaging were performed using a JEM-2100 operated at 200 kV. All the TEM examinations were conducted in the cathode active layer. Chemical analysis was carried out under TEM using energy dispersive X-ray Spectroscopy (EDS). High-angle annular dark-field (HAADF) Z-contrast imaging and nanoscale chemistry analysis were performed using an Aberration-Corrected 200 kV (JEOL 2100F) STEM with the inner cut-off angle of the HAADF detector set at >52 mrad.
As shown in
To identify the physical origin of cell performance enhancement and the slightly increased polarization registance, the dynamic constant in the impedance data was retrieved by evaluating the relaxation times and relaxation amplitude of the impedance-related processes using deconvolution (Refs. 13-14) shown in
The operation also introduced an increase in the P3 peak in the ALD-coated cell, Cell #2, at high-frequency range 4752-9000 Hz. It has been suggested previously that Peak P3 may be associated with charge transfer across the electrode/electrolyte interface, which is independent of the oxygen partial pressure (Ref. 19). Accordingly, P3 is expected to be present in both the exemplary ALD-coated cell and the baseline cell. Without wishing to be bound by a particular theory, the increase of P3 can be related to the formation of insulating phases in the cathode. For example, a possibility is formation of a SrZrO3 phase takes place at the interface between the SDC barrier layer and the LSCF due to the solubility of Sr in the barrier layer phase.
Based on the impedance deconvolution, the subsequent equivalent circuit fitting and the capacitance analysis was performed (see herein below). The ALD-coated cell, Cell #2, had lower chemical capacitance than the baseline cell, Cell #1, suggesting less involvement of the cathode backbone through the oxygen reduction reactions and related mass and charger transfer (Ref. 20). Furthermore, the ALD-coated cell, Cell #2, appears to be associated with continuous reduction of chemical capacitance (Refs. 43-44), with the increase of operation, revealing the continuously increased surface transport and reactions in the overall electrode reaction in the ALD-coated cell.
Overall, the ALD-coated cell exhibited slightly higher Rp for both ORR and oxygen transport. The increased power density can be attributed to the decreased Rs, suggested that the ALD coating has introduced additional mass or charge transfer pathways. Post-mortem nanostructural examination indicated that the ALD layer had a thickness of ˜10 nm and appeared to be fully conformal, dense, and uniform (see
Underneath the superjacent layer, an ultra-thin layer was confined at the interface between CoOx and the LSCF bulk phase (see
The increased conductivity induced by the ALD layer appeared to be tunable by adjusting the loading of the Pt. ALD-coated cell, Cell #4, had a Pt loading that was doubled compared to ALD-coated cell, Cell #2. ALD-coated cell, Cell #4, when operated at 650° C., the initial peak power density was 0.578 W/cm2 at 0 h, and 134% over the baseline cell no. 3 of 0.463 W/cm2 (shown in
A deconvolution study indicated that peak of P1 of the baseline cell, Cell #3, was close to that of P1 of a baseline cell, Cell #1, operated at 750° C. However, there was a large increase in the P2 in the ALD-coated cell, Cell #4. Without wishing to be bound by a particular theory, it is believed that this could be attributed to the increased resistance of O2 transport when the operating temperature was lowered from 750° C. to 650° C. The P1 from the ALD-coated cell, Cell #4, was higher than the baseline cell, Cell #3, suggesting a slightly higher ORR resistance after ALD coating. However, the P2 for ALD-coated cell, Cell #4, was much lower, indicating accelerated oxygen transport along the surface due to the ALD coating layer. Interestingly, for ALD-coated cell, Cell #4, both P1 and P2 remained at their same positions, suggesting that the surface layer was very stable upon the electrochemical reactions for over 800 h. Furthermore, both P1 and P2 decreased significantly, showing slight but continuous improvement of the oxygen surface exchange, oxygen adsorption/desorption, dissociation, and/or surface transport. As shown in examples herein below, there was decreased chemical capacitance (Refs. 43-44), suggesting less involvement of the cathode bulk in the overall electrode reaction in the ALD-coated cell.
Post-mortem nanostructural examination indicates that the ALD layer remained intact and has the same morphology of that as-deposited state and is conformal on both the LSCF and SDC grain surfaces after operation for 816 h (shown in
Based on the results of both ALD-coated cells, i.e., Cell #2 and Cell #4, the ORR pathways and the schematics for possible surface nanoionics of LSCF cathode are suggested as shown in
Without wishing to be bound by a particular theory, the CoOx layer is fully dense and has low oxygen permeability, it is possible that Pt has an effective pathway to access oxygen. Further, without wishing to be bound by a particular theory, it is believed that Pt at the interface primarily can facilitate the formation of the CoOx layer and further stabilize this layer over the cell operation. Without the Pt, an ALD coating of unary CoOx cannot form a conformal CoOx layer on either LSCF or SDC grains (Ref. 24). In the exemplary cells disclosed herein, discrete nano-Pt is immiscible with its neighboring CoOx and LSCF phases. Further, without wishing to be bound by a particular theory, it is believed that nano-Pt may provide interface strain to stabilize the formation of the conformal nanoionics (Refs. 25-26). It is worthwhile to point out the higher Pt loading in ALD-coated cell, Cell #4, did not promote the conductivity. The CoOx+Pt coating layer in ALD-coated cell, Cell #4, reduced 34% Rs over the baseline cell, while the reduction of Rs was 39% for ALD-coated cell, Cell #2, with only half Pt loading. Further, without wishing to be bound by a particular theory, it is believed that nano-Pt at the interface between CoOx phase and LSCF phase might have negative impact to the cathode conductivity. It is reported that the difference in the Fermi level can result in the occurrence of electronic/ionic charge redistribution for the oxide surrounding the Pt particles (Ref. 27). Pt changed the oxide with which it is in contact into a resistance phase, resulting in the formation of a resistive oxide layer on the surface of Pt. Therefore, in the disclosed ALD-coated cells, it may useful to control the maximum loading of dispersed Pt embedded at an interface to facilitate the percolation network and avoid the formation of a continuous resistance layer around Pt.
Overall, the ORR pathways can be shifted from the original LSCF surface to the CoOx surface in the ALD-coated cells. Though the more active LSCF surface is covered, a full extension of the CoOx active sites to the entire backbone surface is obtained. Also, the dissociated oxygen ion can only transport via the CoOx intergranular grain boundaries due to the existence of a fully dense CoOx outer shell layer.
Besides acting as catalytic oxygen reduction sites, the single 7-10 nm CoOx layer appears to carry sufficient conductivity in view of the foregoing data. The bulk scale Co3O4 phase may be an amphoteric semiconductor with intragranular low electronic conductivity (˜2 S cm−1 at 600° C.; see Ref. 28) and was two orders of magnitude lower than bulk LSCF (˜100 S cm−1 at 600° C.). However, a 133-134% cell performance enhancement may be primarily attributed to the decreased Rs (Ref. 3). Without wishing to be bound by a particular theory, it is believed that increased conductivity induced by the conformal CoOx layer was facilitated by fast ion transport through the high-density, high-density grain boundaries, including the surface grain boundaries from the single-layered CoOx nanograins (Refs. 29-34). In general, the high series resistance in the oxygen electrode may be due to the low mobility of the ionic charge carriers and their mechanical and Coulombic interactions with their host crystal structures (Ref. 34). Error! Bookmark not defined.By contrast, in comparison with the intragrain conductivity, there is faster oxide-ionic conductivity along grain boundaries that are commonly associated with higher oxygen vacancy concentration. One example is that La0.8Sr0.2MnO3 (LSM) grain boundaries exhibits 5-6 orders of magnitude of enhancement in oxide-ion diffusivity compared with the bulk LSM. The enhancement might be associated with strain-induced defects and corresponding changes in the oxidation states of LSM constituent cations (Ref. 30, 34-35). Dominating of ionic conductivity at the grain boundary level has been previously reported for La0.6Sr0.4CoO3 (Ref. 36-37) In terms of high ionic conductivity of Co-based nanograins, the formation of (MnCo)Ox nanoionics implanted on the surface pure electronic conductor LSM was previously demonstrated (Ref. 38). However, for the mixed conducting LSCF/SDC backbone, it has not been shown heretofore and the present study is the first demonstration of electrocatalytic surface nanoionics that are implanted on the surface of the inherently functional SOFC. Such surface nanoionics, as disclosed herein, enable a nanostructured electrode—which has been pursued for decades for practical SOFC.
In addition, to facilitate the formation of nanoionics and prevent Sr surface segregation, the ALD coating further tuned the conductivity through the simultaneously formed Sr-enriched interface layer. The impact of this Sr-enriched layer on the conductivity of LSCF grain appears to be at least two-fold.
Firstly, for the Sr-enriched layer alone, when Sr2+ replaced Fe or Co cations with a higher valence state, it caused a decrease in the charge carrier concentration and led to lower electrical conductivity. Meanwhile, there was a small amount of Co cations substituted for the Fe in the Sr-enriched layer, evidenced by the presence of a small amount of Fe cation inside the CoOx coating layer. For the perovskite LSCF, Co ions on the Co/Fe sites can have smaller binding energy for oxygen than that with Fe ions (Refs. 3, 39). Without wishing to be bound by a particular theory, it is believed that increasing the Co content can increase the electrical conductivity. Accordingly, the decreased electrical conductivity due to Sr enrichment can be compensated by Co substitution of Fe. Meanwhile, when a stable valent cation (Sr+2) replaces a multivalent cation (oxidation state +3 and +4) in the system, the charge compensation of B-site cation can be achieved by the development of oxygen-deficient nonstoichiometry (Ref. 40). Further, without wishing to be bound by a particular theory, it is believed that the Sr-enriched layer has high oxygen vacancy and possesses high ionic conductivity.
Secondly, the Sr-enriched layer imposed a strain field at its lateral interface with the LSCF grain surface. The Sr-enriched layer possessed the same perovskite structure of that LSCF, shared the same kind of atomic structure in the La/Sr site, and was fully coherent to the LSCF grain as shown in
Such analysis of the impact of the strain field effect of ionic conductivity is consistent with some prior studies. At the interface of laterally aligned heteroepitaxial YSZ film grown on SrTiO3 substrate, up to eight orders of magnitude enhanced conductivity was observed near room temperature (Ref. 41). Such a huge increase of conductivity was ascribed to the lattice expansion of atomic layers of YSZ phase elongated by the SrTiO3 substrate with 7.5% tensile strain. For LSM, it was predicted by Density Function Theory calculation that tensile strain could improve ion diffusion up to 2 orders of magnitude at 800 K by increasing the migration space of oxygen in the lattice and by reducing the bonding strength between the oxygen and cations (Ref. 42). Such an increase of the conductivity of the strained interface are usually achieved in various nanocomposite grown by pulsed laser deposition (Refs. 43-44). Nonetheless, that substrate-strained engineered interface usually needs to be introduced by the epitaxial growth on the substrate with a well-defined orientation. The implantation of such strained interface in the real electrochemical devices with randomly orientated grains has been found to be typically limited. Thus far, there has been no prior suggestion or realization of the strained multi-layer on the SOFC electrode that needs the enhanced interfaces and grain boundaries for increased catalytic activity and conductivity (Refs. 45-47).
In present examples, planar strained lattices were generated spontaneously between the LSCF and Sr-enriched layer that is fully coherent to the LSCF. The strained pathways formed at the interface between the ALD layer and the LSCF, were fully conformal. Once again, when the ALD-coated layer with the strained interface was applied to the internal surface of the cathode, it remarkably decreased the entire cell Rs by up to 40%. As discussed herein below, factoring in the thickness of ALD layer of 10 nm on the internal surface of cathode with micron-sized grains, and taking the cell resistance as the contribution of cathode, anode, and electrolyte, it was roughly estimated that the conductivity of the ALD layer. At 750° C., the conductivity of the ALD layer with the total thickness around ˜10 nm, with the combination of conformal CoOx layer, Sr-enriched layer, and the strained interface, was estimated to have a conductivity of ˜1.27×104 S/cm, was approximately two orders magnitude of that of LSCF at 750° C.
Most importantly, such surface nanoionics are remarkably stable as evidenced by the intact nanostructure of the coating layer even after 816 h of operation at 650° C., as shown in
The present exemplary cells have superior stability at elevated temperatures, ultra-thin electrocatalytic surface nanoionics and are associated with Sr-enriched strained interface phase have become interfaces-dominated for maximized mass transport and oxygen reduction reactions. The disclosed ALD coating appears to be the most promising approach to conveniently utilizing the grain boundary and strain engineering to increase the reaction kinetics of inherent functional devices.
The impedance decovolution were performed based on the well-developed and excised protocals by different researchers (Refs. 16, 48-52). The devolution steps include: (a) processing the out-of-phase impedance Z″ to remove inductance and to extrapolate the Z″ data to very high and very low frequencies; (b) applying the Fast Fourier Transform (FFT) to the Z″ vs frequency data set; (c) dividing each element of the Z″ transform by the equivalent FFT element of the hyperbolic secant function; (d) filtering the dividend to remove high frequency noise; and (e) performing the inverse FFT to produce the deconvolution spectrum. From the deconvolution spectra, the number of arc-forming elements is identified. The protocol (Ref. 48) for obtaining the appropriate equivalent circuit and their best fit parameters requires iterative steps: (a) Prior to fitting the equivalent circuit to the impedance data, the impedance of the equivalent circuit is calculated; (b) the parameters are adjusted to get an approximate match while making sure that the peak frequencies obtained from the deconvoluiton spectra are preserved; (c) Then ZView® software is used to obtain the least squares fit of the equivalent parameters to the data.
Based on the deconvolution spectra and the preceding considerations, the proposed equivalent circuits contain a series resistance, and five arc-generating elements (RQ). The most common RQ is a parallel combination of a charge transfer resistance and a constant phase element CPE. The admittance Y of the CPE is dependent on two parameters, a magnitude |Q| and an exponent n (0<n≤1), Y=|Q|(j
The data and simulation plots for baseline and ALD-coated at 750° C. are shown in
The data and simulation plots for baseline and ALD-coated at 750° C. are shown in
Eq. (1) was used to describe the contribution of each part of col (anode/electrolyte/cathode) for the uncoated cell.
R
Baseline
=R
LSCF
+R
anode
+R
electrolyte Eq. (1)
Where R can be expressed as RsL/W for each component as:
Since L/W ratios are in the same magnitude for each component, we could further simplify the equation. Thus:
Rs
Totbase
=Rs
LSCF
+Rs
anode
+Rs
electrolyte Eq. (3)
Eq. (3) corresponding to the uncoated cell has all of its components in series. In the other hand, for Eq. (4) we consider the composite of ALD coating and LSCF as an equivalent circuit in parallel since the ALD coating is deposited in the LSCF cathode. Thus, the equation for the ALD-coated cell is as follow:
R
ALDcoated
=R
composite
+R
anode
+R
electrolyte Eq. (4)
Where the equivalent circuit for the ALD/LSCF contribution Rcomposite IS:
If we substitute Eq. (5) into Eq. (4), and R is expressed as RsL/W for each component:
Similar to the baseline cell, the LAW ratios are in the same magnitude for each component. Additionally, from the results obtained in the main manuscript we can consider:
Rs
ALDcoated=0.068/0.112RsTotbase Eq. (7)
Thus, with the incorporation of Eq. (7), we have the following equation for the contribution in the ALD-coated cell:
The only different contributing factors between RsALDcoated and RsTotbase is the LSCF and the ALD film. Additionally, by combining Rsanode+Rselectrolyte in Eq. (3) and Eq. (8), we have the following equation:
Further simplification of the Eq. (9) can lead to:
The resistivity values can be expressed for each component as p=Rs*t. Thus, if we replace Rs=p/t in Eq. (14), we have the following equation.
ρfilm=tfilm(ρLSCF/tLSCF)/{[(ρLSCF/tLSCF)/((ρLSCF/tLSCF)−0.3928ρTotbase/tTotbase)]−1} Eq. (15)
tfilm can be approximated as a fraction of tLSCF in accordance to the area ratio between the LSCF and the ALD film calculated from the TEM images shown in the manuscript. This approach limits the big difference of the actual volume between LSCF cathode and ALD-coated cathode. Additionally, from the manufacturer, we could obtain the thickness of the LSCF and the whole thickness of the cell. The μLSCF value is obtained from literature (Ref. 48) while the ρTotbase is calculated from Rs=p/t.
The resistivity value for the film can be calculated employing Eq. (15). The resultant resistivity value obtained for the film is ρfilm=7.87×10−5 Ωcm, such value represents a ratio of μLSCF/ρfilm of 127. However, the conductivity value for the film is 1.27×106 S/m. Accordingly, we can conclude that the ALD film layer is 127 times more conductive than the LSCF cathode.
The ability to manipulate the surface chemistry of the mixed conductor and suppress its degradation related to the intrinsic Sr surface segregation is critical for the SOFCs. The disclosed ALD-coated cells demonstrate that, for the inherent functional SOFC with a mixed conducting composite cathode, the electrocatalytic nanoionics with high-density grain boundaries can be precisely introduced onto the cathode backbone. The conformal thin-film surface nanoionics can be controlled to have the single-layered, randomly orientated nanograins to maximize the contribution of surface grain boundaries and the interface strains to the conductivity and the electrocatalytic activities. The conformal ALD layer completely shifted the ORR reduction pathways. It also served as the effective barrier layer for backbone cations outward diffusion. Most importantly, the ALD coating turns the original perovskite surface that is vulnerable to cation segregation and degradation into an embedded strained interface phase with enormous conductivity. For the first time in the field of SOFC, the disclosed ALD-coated cells demonstrate an effective approach for solving multiple-problems for successfully suppressing the Sr surface segregation of mixed conductors, preventing Cr contamination, and simultaneously increasing the conductivity. The high-density surface and intergranular grain boundaries of the strained ALD layer provided an enormous surface area
This application claims the benefit of U.S. Provisional Application No. 63/176,672, filed on Apr. 19, 2021, which is incorporated herein by reference in its entirety.
This disclosure was made with U.S. Government support under grant numbers DE-FE0031665, DE-FE 0031251, and DE-FE0026167, awarded by the Department of Energy, and grant number NSF-DMR 1916581, award by the National Science Foundation. The U.S. government has certain rights in the disclosure.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/025351 | 4/19/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63176672 | Apr 2021 | US |
