Development of cathode Architectures customized for H2/O2 metal-cation-free alkaline membrane fuel

Aqueous-electrolyte-free (metal-cation-free) alkaline membrane fuel cells represent a promising new class of low-temperature Pt-free fuel cell. A current hypothesis is that mass transport of (stoichiometric) reactant water to the cathode catalyst reaction sites is the principal origin of the limited power output (water is not a direct reactant in proton-exchange membrane fuel cells (PEMFCs) and only required to keep the proton-exchange membrane hydrated for sufficient conductivity); electrode architectures specifically optimized for use in H-2/O-2 solid polymer electrolyte alkaline fuel cells (SPE-AFC) were previously identified as a research priority. This study directly addresses this challenge and shows that with the correct choice of cathode components significant improvements in power perfort-nance can be obtained; 125 mW cm(-2) was obtained in a H-2/O-2 SPE-AFC when a cathode fabricated from Toray carbon paper and Pt/C catalyst (20% mass Pt on Vulcan XC-72R carbon support) was used with a 79 mu m thick anion-exchange membrane in hydroxide anion form (cf. 94 MW cm(-2) when the same membrane was used with prefabricated Pt-based commercial carbon cloth electrodes that contained 4 mg cm(-2) metal loadings and poly(tetrafluoroethylene), PTFE, binder). Importantly, the cathode fabrication methodology reported will allow the easy comparison of the performance of different cathode catalysts, including Pt/C and cheaper carbon-supported non-noble-metal-containing catalysts of different formulations (e.g., different carbon supports and metal particle sizes). A final significant finding was that Pt-free Vulcan XC-72R-only cathodes can produce between 25% and 36% of the power obtained when Pt/C catalysts were used in SPE-AFCs (this is not the case with PEMFCs where carbon is electrokinetically inactive for the oxygen reduction reaction at the cathode); this insight highlights the necessity of recording the background currents, arising from the carbon supports, when testing different catalyst formulations in alkaline media. A recommendation is presented for a standardized test protocol for evaluating these inherently CO2-tolerant fuel cells.