Mixed Metal Oxides for Oxygen Reduction Reaction: Strategies for Suppressing H₂O₂ Formation

Abstract

Widespread implementation of fuel cell technology has been hampered by challenges originating from the oxygen reduction reaction (ORR). Even the most advanced ORR catalysts present high overpotentials and poor selectivity for the reduction of O2 to H2O. A substantial amount of H2O2 is generated as a product of incomplete reduction. We developed a series of cost-effective cobalt-doped copper oxide (Cu[Co]Ox) catalysts supported on Au. These catalysts not only show lower overpotentials but also very high selectivity for the complete reduction of O2 to H2O. Specifically, Cu-rich compositions, such as Cu0.8Co0.2Ox/Au, demonstrated remarkable activity and > 97% selectivity for H2O over a sizeable potential range (1.0 – 0.6 V) relevant to ORR. These catalysts were found to even outperform Pt in both activity, selectivity, and performance stability. These catalysts have been investigated using in situ Raman Spectroscopy and X-Ray Photoelectron Spectroscopy. Our studies indicate that the doped materials have a Co-active site embedded within the CuOx framework. The resulting sites lower the free energy of the potential determining step and enhance yield for the complete reduction to H2O. Specifically, these catalysts preferentially cleave the O-O bonds result in high selectivity for the 4e pathway. Figure 1