Web Release Date: November 10,
Development of Cathode Architectures Customized for H2/O2 Metal-Cation-Free Alkaline Membrane Fuel Cells
and
Department of Chemistry, The University of Surrey, Guildford GU2 7XH, United Kingdom
Received: August 22, 2007
In Final Form: September 24, 2007
Abstract:
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 H2/O2 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 performance can be obtained; 125 mW cm-2 was obtained in
a H2/O2 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 
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.
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