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Abstract

A modular, multicomponent catalyst design principle is introduced and exemplified using a three-component, oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst designed for the oxygen electrode of unitized reversible fuel cells (URFCs). The catalyst system exhibited unprecedented catalytic performance in liquid electrolyte and in single unitized reversible fuel cell tests. The distinct components, each active for either ORR or OER, are prepared and optimized independently of each other and physically mixed during electrode preparation. The new modular URFC catalyst, Cu-α-MnO₂/XC-72R/NiFe-LDH, combined a carbon-supported, Cu-stabilized α-MnO₂ ORR catalyst with a NiFe-LDH OER catalyst and displayed improved activity and stability under URFC cycling compared to platinum group metal references. Stepwise modular optimization of the carbon and the interlayer anions of the OER component led to a further improved derivative, Cu-α-MnO₂/O-MWCNTs/NiFe-LDH-Cl^–. This URFC catalyst outperformed all previous materials in terms of its combined overpotential η_ORR-OER and performance stability in the rotating disk electrode (RDE) scale. Its single-cell performance is analyzed and discussed.