Benchmarking the Oxygen Reduction Electroactivity of First-Row Transition-Metal Oxide Clusters on Carbon Nanotubes

Transition-metal oxide/nanocarbon hybrids are known to deliver a cooperative oxygen reduction reaction (ORR) with a synergistic effect of the hybrid interface. This work assesses a series of first-row transition-metal oxides in the form of surface-confined clusters on carbon nanotubes, as a mimic of fully exposed hybrid interfaces, providing an activity benchmark for hybrid catalysts. Among the selected metal oxides, MnOx and CoOx; are found to be the most active first-row transition-metal oxide clusters for the ORR, given their excellent peroxide-reducing capability at low overpotential. FeC, and CuOx are also active for the same role, except their peroxide-reducing activity is only activated with substantial overpotential. Other metal oxides (NiOx and ZnOx) do not appear to show any activity toward the ORR, even with an integrated interface as a source for the possible synergistic effect.