Analysis of the limitations in the oxygen reduction activity of transition metal oxide surfaces

The oxygen reduction reaction (ORR) is the key bottleneck in the performance of fuel cells. So far, the most active and stable electrocatalysts for the reaction are based on Pt group metals. Transition metal oxides (TMOs) constitute an alternative class of materials for achieving operational stability under oxidizing conditions. Unfortunately, TMOs are generally found to be less active than Pt. Here, we identify two reasons why it is difficult to find TMOs with a high ORR activity. The first is that TMO surfaces consistently bind oxygen atoms more weakly than transition metals do. This makes the breaking of the O-O bond rate-determining for the broad range of TMO surfaces investigated here. The second is that electric field effects are stronger at TMO surfaces, which further makes O-O bond breaking difficult. To validate the predictions and ascertain their generalizability for TMOs, we report experimental ORR catalyst screening for 7,798 unique TMO compositions that generally exhibit activity well below that of Pt.

Automated summary

The oxygen reduction reaction (ORR) is crucial for fuel cell performance, with TMOs offering operational stability but lower activity compared to Pt-based electrocatalysts. The challenges in finding TMOs with high ORR activity lie in weaker oxygen binding on TMO surfaces and stronger electric field effects, making O-O bond breaking difficult. Experimental screening of 7,798 unique TMO compositions confirmed their lower activity compared to Pt.