Abstract
Alkaline polymer electrolyte fuel cells are a class of fuel cells that enable the use of non-precious metal catalysts, particularly for the oxygen reduction reaction at the cathode. While there have been alternative materials exhibiting Pt-comparable activity in alkaline solutions, to the best of our knowledge none have outperformed Pt in fuel-cell tests. Here we report a Mn-Co spinel cathode that can deliver greater power, at high current densities, than a Pt cathode. The power density of the cell employing the Mn-Co cathode reaches 1.1 W cm−2 at 2.5 A cm−2 at 60 oC. Moreover, this catalyst outperforms Pt at low humidity. In-depth characterization reveals that the remarkable performance originates from synergistic effects where the Mn sites bind O2 and the Co sites activate H2O, so as to facilitate the proton-coupled electron transfer processes. Such an electrocatalytic synergy is pivotal to the high-rate oxygen reduction, particularly under water depletion/low humidity conditions.
Highlights
Alkaline polymer electrolyte fuel cells are a class of fuel cells that enable the use of nonprecious metal catalysts, for the oxygen reduction reaction at the cathode
We report an unexpected finding that the Mn-Co spinel catalyst exhibits activity that is inferior to that of Pt, for oxygen reduction reaction (ORR) in rotating disk electrode (RDE) tests, but superior performance in alkaline polymer electrolyte fuel cells (APEFCs) tests, in particular under low-humidity conditions
A negative shift of 50 mV in the half-wave potential clearly indicates that the ORR occurs at a lower rate on Mn-Co spinel (MCS) than on Pt, and this trend does not change with potential as evidenced in the Tafel plots
Summary
Alkaline polymer electrolyte fuel cells are a class of fuel cells that enable the use of nonprecious metal catalysts, for the oxygen reduction reaction at the cathode. In-depth characterization reveals that the remarkable performance originates from synergistic effects where the Mn sites bind O2 and the Co sites activate H2O, so as to facilitate the protoncoupled electron transfer processes Such an electrocatalytic synergy is pivotal to the highrate oxygen reduction, under water depletion/low humidity conditions. Despite great efforts, the last objective has remained elusive While some materials, such as nitrogen-doped carbon-based materials[15,16], have been suggested to exhibit Pt-comparable activity towards the oxygen reduction reaction (ORR) in alkaline media, their performance is still much lower than that of Pt in APEFCs17,18, especially when operated at high current densities necessary in automotive applications. Such a mechanism is pivotal in APEFC cathode, where water is a reactant but usually depleted
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