Patent Application
20160226077
This disclosure relates to non-carbon mixed material electrocatalyst support structures, and in particular, to a high surface area metal oxide support doped with a conductive metal used to produce electrocatalysts for hydrogen fuel cell vehicles having active catalyst particles deposited thereon.
Carbon has traditionally been the most common material of choice for polymer electrolyte fuel cell (PEFC) electrocatalyst supports due to its low cost, high abundance, high electronic conductivity, and high Brunauer, Emmett, and Teller (BET) surface area, which permits good dispersion of platinum (Pt) active catalyst particles. However, the instability of the carbon-supported platinum electrocatalyst due at least in part to carbon corrosion is a key issue that currently precludes widespread commercialization of PEFCs for automotive applications.
The adverse consequences of carbon corrosion include (i) platinum nanoparticle agglomeration/detachment; (ii) macroscopic electrode thinning/loss of porosity in the electrode; and (iii) enhanced hydrophilicity of the remaining support surface. The first results in loss of catalyst active surface area and lower mass activity resulting from reduced platinum utilization, whereas the second and third result in a lower capacity to hold water and enhanced flooding, leading to severe condensed-phase mass transport limitations. Clearly, both consequences directly impact PEFC cost and performance, especially in the context of automotive stacks.
To address the issues with carbon-based catalyst, non-carbon alternatives are being investigated, such as metal oxides. However, some metal oxides alternatives are cost-prohibitive, and dissolution, agglomeration and corrosion of the metal oxide alternatives can still occur.
Non-carbon support particles are disclosed for use in electrocatalyst comprising a first metal oxide having a high surface area doped with an electrically conductive transition metal. An example of non-carbon support particle for use in electrocatalyst as disclosed herein comprises titanium oxide particles doped with ruthenium.
These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims and the accompanying figures.
The various features, advantages and other uses of the present apparatus will become more apparent by referring to the following detailed description and drawing in which:
One example of a non-carbon metal oxide catalyst support consists essentially of a non-conductive metal oxide having a high surface area. A non-limiting example of such a metal oxide is titanium dioxide. Titanium dioxide (TiO2) has very good chemical stability in acidic and oxidative environments. However, titanium dioxide is a semiconductor and its electron conductivity is very low.
To overcome the deficiencies of the non-conductive metal oxide alone, a non-carbon metal oxide support having both a non-conductive oxide and a conductive metal have been developed. Disclosed herein are non-carbon support particles for use in electrocatalyst comprising a metal oxide having a high surface area doped with an electrically conductive transition metal. Doping the high surface area metal oxide with a conductive transition metal provides the requisite electron conductivity. Doping the conductive transition metal can also reduce or eliminate dissolution and agglomeration of the metal that can arise when one particle is deposited on another particle, as doping chemically bonds the conductive metal to the metal oxide support. The doped support particle provides greater stability than support particles comprised of a conductive metal deposited on a non-conductive, high surface area metal oxide. Doping the metal oxide with the conductive metal also maintains the high surface area of the metal oxide support on which the active catalyst particles are deposited.
The metal oxide in the catalyst support particles 18 is a high surface area metal oxide with low electron conductivity. As used herein, “low electron conductivity” refers to those metal oxides having insufficient electron conductivity to be used solely as the electron conductor in fuel cell catalyst and include metal oxides that do not conduct electrons. The metal oxide can be one or more metal oxides prepared with varying ratios of metal oxides and various particle sizes depending on the metal oxides used. As non-limiting examples, the metal oxide in the catalyst support particles 18 can be titanium dioxide.
The metal oxide of the catalyst support particles 18 is doped with a conductive metal, preferably a conductive transition metal. As a non-limiting example, the transition metal can be ruthenium. The metal oxide will have a larger particle size than the conductive transition metal and be doped with the conductive transition metal, making the catalyst support particle 18 electron conductive while maintaining the high surface area.
Active catalyst particles 20 are deposited onto the catalyst support particles 18. The active catalyst particles 20 can include one or a combination of precious metals such as platinum, gold, rhodium, ruthenium, palladium and iridium, and/or transition metals such as cobalt and nickel. The precious metal can be in various forms, such as alloys, nanowires, nanoparticles and coreshells, which are bimetallic catalysts that possess a base metal core surrounded by a precious metal shell.
The conductive metal oxide can be an oxide of the conductive transition metal with which the high surface area metal oxide is doped. For example, the conductive transition metal can be ruthenium and the conductive metal oxide can be ruthenium dioxide. Alternatively, the conductive metal oxide can be an oxide of a different metal than the conductive transition metal. For example, the conductive transition metal can be ruthenium and the conductive metal oxide can be iridium oxide. The high surface area metal oxide can have a particle size greater than the particle size of the conductive metal oxide.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
