Catalyst or Precatalyst? The Effect of Oxidation on Transition Metal Carbide, Pnictide, and Chalcogenide Oxygen Evolution Catalysts

Metal chalcogenides, pnictides, and carbides, labeled collectively as metal X-ides, have become an exciting new class of water oxidation electrocatalysts, but there is a lack of agreement regarding the composition of the "true" catalyst. The most prominent theories are that the X-ides are either completely oxidized, left unoxidized, or transformed into core@shell particles upon testing. Here, we examine examples of each conjecture, summarizing the conflicting viewpoints on catalyst identity and offering guidelines for more rigorous identification in the future. Most studies indicate that at least partial oxidation of the catalyst surface is critical to high performance, likely caused by an increased catalyst surface area upon oxidation or improved charge transfer in the X-ide cores. Therefore, more thorough and uniform long-term testing and nanoscale chemical analysis are essential to determine how these factors relate to catalyst performance.