The present invention concerns the use of a device comprising a porous electrode and an electrically insulating porous layer to remove oxygen in contact with a working electrode. The present invention also concerns the use of said device in contact to said working electrode to detect and/or quantify an analyte in presence of oxygen.
Electrochemical techniques offer the advantage of being label-free, rapid, simple and cost-efficient. Nevertheless, an intrinsic problem in electroanalytical detection is that the analytical current is the sum of all (possibly interfering) currents of the electroactive species present in solution, including oxygen from air. Moreover, oxygen can be competing during the detection of some species, e.g. low metal concentration, leading to a degradation of the analytical performances of the sensor.
Indeed, oxygen is soluble in water and is therefore likely to be found in aqueous solutions that are in contact or have been in contact with air.
However, some sensing reactions in aqueous media are hindered by the presence of dissolved oxygen. Thus the removal of dissolved oxygen plays a crucial role in these sensor applications, notably under ambient air. In particular, it is often necessary to detect a given analyte in aqueous medium at a small concentration. But this detection cannot be performed in presence of dissolved oxygen, the detection efficiency depending on the O2 removal ability since oxygen induces a significant error in analyte detection, especially at very low analyte concentrations.
Therefore, in many cases, oxygen has to be removed from water as completely as possible.
Present methods of oxygen removal are physical or chemical deoxygenation. An easy and common physical method to eliminate dissolved oxygen is purging solution with nitrogen or argon. The main disadvantages of the physical methods is the high capital cost, for example in outdoor applications where compress nitrogen or argon needs to be carried by the user.
Chemical deoxygenation is based on chemicals reacting with oxygen. To avoid using of N2 or Ar, ascorbic acid has been used as a reducing agent to remove interfering oxygen for the greenhouse gas nitrous oxide (N2O) detection which is very sensible toward dioxygen. Other oxygen scavengers like sodium thiosulfate (Na2S2O3), phosphines, also proved its efficient ability for this purpose. The sensing of H2O2 could be done under both air-saturated and O2-saturated solution at polyaniline modified Pt electrode by adding Na2S2O3 with concentration below 1 mM. For application in N2O sensor, phosphines soluble in organic solvents showed a high sensitivity and long response time. An enzymatic oxygen scavenging system using different oxidase enzymes such as glucose, galactose or pyranose 2-oxidase as effective catalysts for O2 reduction has been known recently. One of the main drawbacks with the chemical and enzymatic methods is the need of a continuous addition of reagent to the reactor.
Accordingly, it is an object of the present invention to provide devices, uses and processes that have high efficiency with a low energy and chemicals consumption.
Inventors have for the first time demonstrated that devices, uses and processes of the invention enable to only remove oxygen in an area confined to the surface of the sensor, quickly allowing an oxygen concentration close to zero in this area, and therefore optimal operation of the sensor, without the need to consume all the oxygen in the solution (which is difficult to achieve and in any case more time consuming and more expensive). The removal of oxygen is paired with the formation of water only, with no formation of unwanted compounds like H2O2.
Moreover, it is advantageous to avoid the use of toxic deoxygenation chemicals.
Thus, in one aspect, the present invention relates to the use of a device comprising:
In another aspect, the present invention relates to a process of reducing or removing oxygen from a solution in contact with a working electrode comprising the steps of:
In another aspect, the present invention relates to the use of a device comprising:
to detect and/or quantify an analyte dissolved in a solution further comprising oxygen.
In another aspect, the present invention relates to a process of detecting and/or quantifying an analyte dissolved in a solution further comprising oxygen, comprising the steps of:
In particular, and further to the working electrode defined above (also referred as the first working electrode), the porous electrode is a second working electrode. Indeed, the porous electrode is a working electrode enabling the reduction of dissolved oxygen into water, whereas the first working electrode is a working electrode as well known by the skilled person in the art, in particular in the context of electroanalysis of a given analyte, within a electrochemical sensor, of electrochemical conversion, for example NAD(P)+ regeneration, or as a biocathode, for example for the nitrate reduction.
In a particular embodiment, the porous electrode is constituted of or comprises a metal and/or carbon.
In a particular embodiment, the porous electrode is constituted of or comprises at least one porous, electrically conductive material, in particular chosen from metal grids, metal meshes, metal nets, metal lattices, carbon papers, more particularly graphitized or carbonized carbon fiber papers, metallized carbon paper, carbon fiber nonwovens, woven carbon fiber fabrics, carbon or graphite felts, beds of carbon or graphite particles, or combinations thereof.
It is noted that the porous electrode may be constituted of or comprised a plurality of the above-mentioned materials, for example a plurality of metal grids, more particularly 2 or 3 stacked metal, for example Pt, grids.
In a more particular embodiment, the metal is chosen from the group comprising platinum, stainless steel, palladium, rhodium, ruthenium, gold or combinations thereof.
In a more particular embodiment, the metal of the porous electrode is constituted of or comprises a platinum or stainless steel grid or mesh.
In a more particular embodiment, the carbon is chosen from carbon papers.
In a more particular embodiment, the carbon is chosen from the group comprising metal modified carbon papers, in particular platinum modified carbon papers, more particularly platinum coated carbon papers.
As mentioned above, the metal the porous electrode may be constituted of or comprise a plurality of modified carbon papers, in particular platinum modified carbon papers, more particularly platinum coated carbon papers, for example 2 or 3.
In a particular embodiment, the thickness of the porous electrode is comprised from about 1 to about 1000 μm, in particular from about 10 to about 200 μm, more particularly from about 50 to about 100 μm.
In a particular embodiment, the size of the pores of the porous electrode is comprised from 1 to 500 μm in particular from about 10 to about 250 μm.
In a more particular embodiment, the size of the pores of the porous electrode is comprised from 1 to 500 μm in particular from about 10 to about 250 μm, and the thickness of the porous electrode is comprised from 2 to 10 times the size of the pores of the porous electrode, notably from 2 to 5 times.
In a particular embodiment, the electrically insulating porous layer is constituted of or comprises a polymer, or an inorganic material.
In a particular embodiment, the electrically insulating porous layer is constituted of or comprises a membrane, grid, mesh, woven fiber fabric, fiber nonwoven, in particular a polymer membrane or a polymer grid, more particularly a polyamide grid.
Said membrane is for example a membrane for filtration, as well known by the skilled person in the art.
In a more particular embodiment, the polymer is chosen from polyamide, polyimide, polyester, polyethylene, polytetrafluoroethylene.
In another more particular embodiment, the inorganic material is chosen from glass, in particular sintered glass, and ceramics, in particular sintered ceramics, said ceramics being notably made from clay, quartz, alumina, feldspar or their mixtures.
In a particular embodiment, the thickness of the electrically insulating porous layer is comprised from about 10 nm to about 500 μm, in particular from about 1 μm to about 200 μm, more particularly from about 10 to about 100 μm, even more particularly from about 50 to about 100 μm.
In a particular embodiment, the size of the pores of the electrically insulating porous layer is comprised from 0.002 to 500 μm, in particular from about 0.1 μm to about 100 μm.
In a more particular embodiment, the size of the pores of the electrically insulating porous layer is comprised from 0.002 to 500 μm, in particular from about 0.1 μm to about 100 μm, and the thickness of the electrically insulating porous layer is comprised from 2 to 10 times the size of the pores of the electrically insulating porous layer, notably from 2 to 5 times.
The applied potential is a potential that enables the conversion of dioxygen into water thanks to the porous electrode (“second working electrode”). This applied potential is easily determined by the skilled person in the art, for example by varying said potential and note the values that enable a good conversion of dioxygen into water.
In a particular embodiment, the potential applied during step b) is a fixed potential.
In a particular embodiment, the potential applied during step b) is a potential comprised from 2 to −1 V, in particular vs. Ag/AgCl, more particularly of about 0.6 to about −0.8 V vs. Ag/AgCl.
For example, the potential may be of about −0.7 V vs Ag/AgCl for a stainless steel based porous electrode (“second working electrode”), or of about −0.4 to about −0.3 V vs Ag/AgCl for a platinum based porous electrode (“second working electrode”).
In a particular embodiment, the analyte is chosen from:
In a particular embodiment, the working electrode is a porous working electrode.
In another aspect, the present invention concerns a device comprising:
All the particular embodiments mentioned above are applicable here, alone or in combination.
In another aspect, the present invention concerns a process of preparation of a device as define above, comprising:
The two steps can be performed in any order, in particular in the order as mentioned above.
In particular, the two contacting steps, independently from each other, can be performed by any mechanical methods known by the skilled person in the art, for example by mechanical pressing, gluing or using an adhesive, preferably on the periphery of the device to obtain.
The following terms and expressions contained herein are defined as follows:
As used in this description, the term “about” refers to a range of values of ±10% of a specific value. For example, the expression “approximately 100 μm” includes values of 100 μm±10%, i.e. values from 90 μm to 110 μm.
As used herein, a range of values in the form “x-y” or “x to y”, or “x through y”, include integers x, y, and the integers therebetween. For example, the phrases “1-6”, or “1 to 6” or “1 through 6” are intended to include the integers 1, 2, 3, 4, 5, and 6. Preferred embodiments include each individual integer in the range, as well as any subcombination of integers. For example, preferred integers for “1-6” can include 1, 2, 3, 4, 5, 6, 1-2, 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, 2-6, etc.
By “porous” is in particular meant a material containing pores, arranged in such a way that a liquid, in particular an aqueous solution, is able to circulate through the material.
By “pore” is in particular meant a cavity in a material, said cavity being for example located within the material, or in contact with one or more of the surfaces of the material.
Stainless steel (SS) and Platinum (Pt) grid were purchased from Goodfellow SARL with purity of 99.9%. Membrane filters (DVPP), glassy carbon (GCE) electrode were bought from Merck Milipore and Sigradur HTWHochtemperatur-Werkstoffe, Germany, respectively.
The electrochemistry cell was composed of four electrodes and fabricated from Teflon material with cylindered form as depicted in
The oxygen removal was investigated by scanning WE1 (Glassy carbon) in the absence or presence of SS as WE2 at fixed potential. Without applying WE2, a broad oxygen reduction in the range −0.4 V->−0.8 V was observed on WE1. However, once the second electrode was polarized at potential of −0.7 V, the reduction wave on WE1 was very straight with complete disappearance of oxygen peak. The experiment was repeated by stirring solution in 30 min and done again the polarization steps. The similar behavior was repeatable from the first cycle to third cycles and fifth cycle. The obtained results confirmed strongly that the oxygen was nearly removed totally at surface of WE2 and prevented from reaching WE1. The comparison experiment was performed under nitrogen atmosphere. The oxygen consumption at WE2 was even better than by nitrogen saturation where a small peak with very low current was observed around −0.5 V on
The oxygen removal efficiency at WE2 using the designed electrochemistry cell was also proved by replacing SS by another material like Pt. The acquired electrochemical feature on CV waves in both case of using and without WE2 were similar to the above results for SS. Regarding on
In sensor application, the presence of hydrogen peroxide can create some negative effects because of its high oxidation property which often used as oxidant. Therefore, the oxygen removal without H2O2 production is also an important factor to evaluate the efficiency of the designed cell. The testing experiments were performed by scanning WE1 in the range 1.0 V->−1.2 V under applying of SS (WE2) at −0.7 V and adding H2O2 concentration from 0 mM to 1.6 mM or 3.2 mM. The addition of H2O2 increased clearly the anodic response near 0.6 V, which came from the H2O2 oxidation. There was no peak observed in this area on the curve obtained with no H2O2 addition, proving that the deoxygenation on WE2 did not generated other side products like H2O2.
Paraquat (1,1-dimethyl-4,4 bipyridinium dichloride) is a cationic redox chemical compound of the viologen family, highly soluble in water. Paraquat is used as herbicide to control broad leaf weeds in agricultural practices since the 1960s. It is used worldwide in more than 100 countries but is banned in European Union. It causes severe toxicity to living organisms by damaging the lungs, kidneys, liver and heart. It is also reported to cause Parkinson's disease. Therefore, it is necessary to detect this compound at small concentration in aqueous medium. At low concentration, paraquat is detected by electrochemical method via running the cycle voltammograms. There is the appearance of two successive one electron reactions at −0.7V and −1.025V on reduction curve and then oxidize back to the relative potential values. However, these processes cannot be observed in case the presence of dissolved oxygen and the detection efficiency depends on the O2 removal ability. For electrochemical sensing of paraquat, study of the first redox reaction is enough to provide sufficient quantification of paraquat in the aqueous media. However, the first single electron reduction of paraquat is at −0.7 V at GCE which is almost at the same potential where reduction of oxygen takes place.
As a result, the signal of paraquat is suppressed (
The paraquat at concentration of 20 μM was detected under air on a silica thin film modified GCE (WE1) using designed electrochemistry cell with the polarization of Pt as WE2 at fixed potential of −0.5 V, as described in Example 1. Sodium nitrate (0.07 M) was used as electrolyte.
The attained result was compared with the one done under N2 saturation or without applying WE2. The CV was also recorded on a Palm Sens 3 potentiostat at a scan rate of 20 mV s−1. All potentials in this study were quoted with respect to the Ag/AgCl.
As described in example 1, WE1 was used for paraquat analysis and WE2 for the continuous reduction of oxygen by applying −0.5V potential during the experiment. In
In this example, two kinds of WE2 materials, SS and Pt, were tested and the similar results were obtained for both. In fact, the polarization of SS at −0.7 V vs Ag/AgCl or −0.4 V vs Ag/AgCl for Pt could eliminate oxygen reduction peaks from −0.4 V to −0.8 V vs Ag/AgCl on the GCE as WE1. The experimental results were repeatable at least to five cycles. Importantly, the experiment about the electrochemical oxidation of hydrogen peroxide confirmed that there was no H2O2 generation during the deoxygenation at WE2. Additionally, the effect of O2 removal was clearly proved in case of using the designed cell to detect an herbicide compound, paraquat. Paraquat at concentration of 20 μM was well detected under air on silica thin film modified GCE (WE1) by applying a fixed potential at −0.5 V on Pt (WE2). The obtained results showed that the O2 elimination at WE2 was better than under N2 atmosphere.
Two experiments are reported here to illustrate the interest of O2 filter for the detection of cadmium.
Coenzyme/cofactor, β-nicotinamide adenine dinucleotide NAD(P)H, has been widely used in biocatalysts as a hydride source for the synthesis of chiral compounds. During the enzymatic reduction process, NAD(P)H played the role of a reductant that is in situ oxidized to NAD(P)+, and the conversion occurs stoichiometrically. Regarding on its high cost, the development of regeneration approaches for continuous recycling of this cofactor is very crucial for practical application. The NAD(P)H regeneration requests transfer of two electrons and a proton to NAD(P)+ from the hydride donors. Among the known methods, the electrochemical NAD(P)H regeneration strategy presents some remarkable advantages relevant to its potentially low cost and without reducing agent addition which is important for the product isolation. However, the interfering oxygen removal is essential to expel the O2 reduction process occurred at the same catalytic potential range on carbon electrodes, which hinders the NAD(P)H regeneration.
Although showing a good efficiency for O2 removal, the oxygen elimination methods of the prior art [e.g. physical (bubbling nitrogen/argon flow in the solution), chemical (adding oxygen reducing agent such as ascorbic acid (C6H8O6)] kill total oxygen species in reaction area and cannot be applied for the electroenzymatic synthesis demanding the O2 supply.
Platinum grid (99.9%) and polyamide—Nylon grid (39 μm wire diameter, 50 μm nominal space) were purchased from Goodfellow, England. Multi-walled carbon nanotubes (MWCNT, >95%, Φ 6-9 nm, L 5 μm).
Removal of Oxygen from Aqueous Medium
The oxygen removal from aqueous medium was carried out in an open cylindrical electrochemical reactor. This system included four electrodes with an Ag/AgCl/1 M KCl (purchased from Metrohm, Switzerland) as reference electrode, platinum grid (0.1 mm wire diameter, 0.4 mm nominal space) as counter electrode, the glassy carbon (GCE) as working electrode 1 (WE1, S=16.61 mm2) and platinum grid (0.04 mm wire diameter, 0.12 mm nominal space) as working electrode 2 (WE2, S=16.61 mm2). The effect of WE2 layer numbers to O2 removal efficiency was simultaneously examined. Between WE1 and WE2 was separated by a porous Nylon grid which allowing oxygen easily transfer from solution to surface of WE1. The connection of both WE1 and WE2 was done via Pt wires. Oxygen presented in 10 mL of supporting electrolyte (KCl 100 mM) under air was eliminated by applying a constant potential (−0.4 V vs. Ag/AgCl) at WE2. The oxygen absence was recorded on WE1 by running cyclic voltammograms using Autolab (PGSTAT 100). A similar experiment was also performed by disconnecting of WE2 to see the O2 presence on WE1. In addition, the O2 disappeared signal in the case of WE2 connection was confirmed by running experiment in a closed reactor under N2 bubbling.
A Bucky paper electrode immobilized with [Cp*Rh(bpy)Cl]+ (BP-Bpy-Rh) was prepared following the protocol published by Zhang et al. (“Electrocatalytic biosynthesis using a bucky paper functionalized by [Cp*Rh(bpy)Cl]+ and a renewable enzymatic layer,” ChemCatChem, 2018). This functionalized electrode was used for NADH or NADPH regeneration by observation of the catalytic peak on BP-Bpy-Rh during NAD+/NADP+ addition. This reaction is very sensitive with O2 presence, so it is essential to avoid completely the oxygen presence. The oxygen removal was also carried out by applying a constant potential (−0.4 V vs. Ag/AgCl) at WE2 as explained above. However, in this case, replacing GCE by BP-Bpy-Rh as WE1 where catalytic response was evaluated by running cyclic voltammetry from −0.4 V to −0.9 V vs. Ag/AgCl at scan rate of 5 mV s−1. Some comparison experiments were done to prove: (1) The O2 removal capacity of WE2 filter by repeating experiment under N2 bubbling; (2) The catalytic role of [Cp*Rh(bpy)Cl]+ for NAD(P)H regeneration by doing experiment with bare electrode (bucky paper) in N2 medium; (3) The sensitivity with oxygen during the reduction of NAD(P)+ by performing experiment under air without WE2 connection.
Towards the bioconversion of D-fructose to D-sorbitol, a compact cell was designed, including different layers. Firstly, D-sorbitol dehydrogenase (DSDH) in silica gel which called DSDH sol was deposited on microfiber filter layer. The DSDH sol was synthesized by stirring overnight a mixture of 0.13 g GPS, 0.18 g TEOS with 0.5 mL water and 0.625 mL 0.01 M HCl. The day after, the sol was diluted three times before mixing 40 μL this aliquot with 20 μL of PEI (20%), 20 μL of H2O and 30 μL of DSDH stock solution. Then, it is necessary to dry this DSDH gel layer at 4° C. overnight. After that, it was put on the top of WE2, following to Nylon separator and BP-Bpy-Rh electrode as WE1. Platinum grid (0.1 mm wire diameter, 0.4 mm nominal space) and Ag/AgCl/1 M KCl were still used as counter electrode and reference electrode, respectively. Prior of experiment, 1 mM NADH was mixed in 10 mL of buffer phosphate solution (PBS, 50 mM pH=6.5). The transformation of D-fructose to D-sorbitol on the surface of DSDH gel layer consumed NADH which was regenerated at WE1. In this system, two layers of platinum grid (0.04 mm wire diameter, 0.12 mm nominal space) was used as WE2 for oxygen filter during the NADH regeneration.
The oxygen removal experiment was carried out in a four-electrode system with platinum grid (0.1 mm wire diameter, 0.4 mm nominal space) as counter electrode, Ag/AgCl/1 M KCl as reference electrode, the glassy carbon (GCE) as working electrode 1 (WE1, S=16.61 mm2) and platinum grid (0.04 mm wire diameter, 0.12 mm nominal space) as working electrode 2 (WE2, S=16.61 mm2). The oxygen presence was detected on WE1, and oxygen was consumed at WE2.
For NAD(P)H regeneration, [Cp*Rh(bpy)Cl]+ was chosen as an efficient non-enzymatic catalyst. The immobilization of [Cp*Rh(bpy)Cl]+ on the surface of bucky paper (BP) was achieved via electro-grafting and complexation steps. By applying a negative potential on the BP-Bpy-Rh electrode, the Rh(III) on the surface of electrode was reduced to Rh(I). The catalytic response of [Cp*Rh(bpy)Cl]+ was noticed around −0.65V by running CV without adding NAD+ in 10 mL of PBS (50 mM, pH=6.5) from −0.4 V to −0.9 V vs. Ag/AgCl. This experiment was performed in above four-electrode cell. Platinum grid (0.1 mm wire diameter, 0.4 mm nominal space) and, Ag/AgCl/1 M KCl were still used as counter electrode and reference electrode, respectively. Applying reduction potential (−0.4 V) at WE2 to remove oxygen approaching to WE1 where the catalytic response of [Cp*Rh(bpy)Cl]+ was observed. The peak at −0.65 V was also obtained when the experiment was repeated under N2 medium. The absence of [Cp*Rh(bpy)Cl]+ immobilization on the surface of BP electrode, there was no peak presented on WE1. The oxygen presence by disconnection WE2 covered the catalytic peak by a large peak in the range from −0.4 V to −0.7 V.
In conclusion, the oxygen presence could be detected while performing NAD+ reduction reaction, and NADH regeneration could be performed under air medium by using the cell of the invention for O2 removal at WE2.
Applying a reduction potential (−0.4 vs. Ag/AgCl) at WE2 which was composed for example by two layers of platinum grid (0.04 mm wire diameter, 0.12 mm nominal space) could remove totally oxygen and no oxygen was detected at WE1 (glassy carbon electrode). Then, NAD+ reduction reaction at the surface of BP-Bpy-Rh electrode was chosen to detect the oxygen presence because of its sensitivity to O2. Without applying WE2, a board peak in the range from −0.4 V to −0.7 V corresponding to O2 presented in solution, hided the catalytic response of rhodium complex. The oxygen removal by filter made the cathodic peak appear around −0.65V without NAD+ addition, and current value increased from 35 μA to 60 μA by adding 0.25 mM of NAD+. The result was repeated by running experiment under N2. This phenomenon also happened in the case replacing NAD+ by NADP+ and the catalytic current reached to the saturated value at 100 μA. Therefore, it could be concluded that NAD(P)+ could be detected under air medium by applying our oxygen filter, and NAD+ reduction reaction is sensitive reaction to O2.
Carbon paper (CP, thickness 80 μm, CeTech GDS090) were bought from FuelCellStore. Sodium hexachloro-platinate (IV) hexahydrate (Na2PtCl6.6H2O, 98%), multi-walled carbon nanotubes (MWCNT, >95%, Φ 6-9 nm, L 5 μm, were obtained from Sigma-Aldrich. Nylon grid (39 μm wire diameter, 50 μm nominal space, Goodfellow), platinum grid (0.04 mm wire diameter, 0.12 mm nominal space, Goodfellow), were used without any purification.
The commercial CP was firstly cleaned in an ultrasonic bath with the mixture of ethanol/H2O to eliminate any impurity resulting from the industrial manufacturing process. In addition, the cleaning step helped to reduce the hydrophobicity of CP, which was necessary for Pt deposition in next step occurred in aqueous medium. This pretreated carbon felt was denoted as raw CP. The Pt was electrodeposited on the surface of CP by the method of CV running 30 cycles from 0 to −1 V vs. Ag/AgCl at a scan rate of 20 mV s−1 in Na2PtCl6 solution under nitrogen atmosphere to avoid the oxygen reduction reaction (ORR). The process was recorded on a Autolab (PGSTAT 100) using a three-electrode system with the CP as working electrode, an Ag/AgCl/1 M KCl (purchased from Metrohm, Switzerland) as reference electrode and platinum grid as counter electrode. After the electrodeposition step, the sample was rinsed and dried at 70° C. The as-prepared sample was labeled as «Carbon paper+Pt» or Pt@CP.
The oxygen filter system was an electrochemical Teflon cylinder cell with round working area of 16.61 mm2. It was compacted of Pt@CP (working electrode 2, WE2), Nylon separator, glassy carbon (working electrode 1, WE1). An Ag/AgCl/1 M KCl and platinum grid as reference electrode and counter electrode, respectively were played in the solution of KCl 100 mM. In this system, WE2 played the role of oxygen filter which prevented O2 molecules passing from solution to WE1. The experiment was perform under convection by stirring at a rate of 800 rpm. The oxygen presence at the surface of WE1 was detected by running experiment from 0 V to −0.9 V vs. Ag/AgCl, and applying a reduction potential at WE2. To evaluate the efficiency of oxygen filter, different parameters were evaluated, including: various amount of Pt deposited on carbon paper, potential valued applied on WE2, number of Pt@CP. The O2 removal by using the filter was confirmed by repeating the experiment under nitrogen bubbling.
The oxygen filter was used to regenerate NADH. To perform this experiment, firstly, a Bucky paper electrode (BP) was prepared from dispersion of MWCNT in 50 mL ethanol by ultrasonication for 5 h. Then the rhodium catalyst ([Cp*Rh(bpy)Cl]+) was immobilized on BP. The NAD+ transformation was carried out via the chronoamperometry experiment with applied potential of −0.78 V. Different amount of NAD+ was added gradually to the buffer phosphate solution (PBS, 50 mM, pH=6.5) to measure catalytic current versus NAD+ concentration recorded on [Cp*Rh(bpy)Cl]+ functionalized Bucky paper electrode (BP-Bpy-Rh). In this case, WE1 was BP-Bpy-Rh, WE2 was Pt@CP and reference electrode as well as counter electrode were kept unchanged. The formed NADH concentration was identified by absorbance at 340 nm by UV-Vis spectroscopy. UV-Vis spectra have been recorded on a Cary 60 Scan UV-Vis spectrophotometer. The NADH regeneration was repeated under nitrogen and air atmosphere (without applying WE2) to compare the faraday efficiency of the transformation.
The oxygen removal was performed in a four-electrode cell, including platinum grid (counter electrode), Ag/AgCl/1 M KCl (reference electrode), glassy carbon (GCE, working electrode 1), and Pt@CP or Pt grid (working electrode 2). Applying a reduction potential (−0.4 V) at WE2 could eliminate completely interference oxygen. The O2 absence on WE1 was confirmed by running CV from 0 V to −0.9 V at a scan rate of 5 mV s−1 in 100 mM KCl under convection. By disconnecting WE2, oxygen presented in the solution under air passed easily to WE2 as well as nylon separator and came to the surface of GCE. Therefore, a huge reduction current was observed around −0.6 V to −0.8 V vs. Ag/AgCl which was assigned for ORR.
To prove the efficiency of the filter for oxygen removal, the experiment was repeated under N2 bubbling in
To carry out this experiment, Bucky paper functionalized by rhodium complex (BP-Bpy-Rh) with 35.3 μm of thickness was placed at WE1 in which happened the NAD+ reduction. Two Pt@CP layers, Ag/AgCl/1 M KCl and platinum grid were kept unchanged as WE2, reference electrode and counter electrode, respectively. The gradual NAD+ concentrations were added in 10 mL solution of PBS (50 mM, pH=6.5) during the chronoamperometry experiment with applied potential of −0.78 V at BP-Bpy-Rh electrode.
Platinum particles were grown successfully on the surface of carbon paper electrode via electrochemical method by running CV Na2PtCl6 solution with 30 cycles from 0 to −1 V vs. Ag/AgCl. The Pt deposited on CP was confirm by various physical characterization such as SEM, XRD and EDX. The electrochemical performance toward the ORR was improved by Pt modification and 0.4 mg cm−2 was chosen as the optimal Pt amount. Then the fabricated Pt@CP was used as material for oxygen filter in a four-electrode cell. Total interference oxygen was removed at filter which was compacted by two Pt@CP layers at applied potential of −0.4 V vs. Ag/AgCl. By evaluating the effect of applied potential at WE2 to the oxygen removal efficiency, it could be noticed that a suitable value could be from −0.3 V to −0.4 V. The O2 elimination capacity of filter was proved by repeating the same experiment under nitrogen atmosphere. Interestingly, oxygen was removed better in case of using the filter of the invention. This brought to more stable of catalytic current during the NADH regeneration at BP-Bpy-Rh electrode. From that, a faradaic efficiency (FE) values of 63.4% was obtained which was nearly 6 times higher than without applying filter at WE2. In conclusion, Pt@CP was an excellent material filter at WE2 to remove completely oxygen under convection, which was very useful for applications in sensing and electrocatalysis.
Number | Date | Country | Kind |
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19188711.6 | Jul 2019 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/069576 | 7/10/2020 | WO |