Challenges and strategies of transition metal phosphides applied in oxygen evolution reaction of electrocatalytic water splitting: A review

Transition metal phosphides (TMPs) have aroused considerable interest as electrocatalysts for the oxygen evolution reaction (OER) in water splitting. Numerous excellent investigations were conducted but several challenges still existed and commonly available strategies were not clear. To our knowledge, reviews in this field only focused on the TMPs catalysts synthesis and their OER performance. However, the summarization about challenges and strategies were ignored. Therefore, this review was guided by the key problems occurred in OER catalyzation by TMPs and proposed the corresponding strategies. The fundamental mechanisms of electrocatalytic water splitting, especially the OER mechanism were initially introduced. The major challenges hindering the application of TMPs were then summarized as instability, weak electrical conductivity and insufficient activating capability. Subsequently, available strategic approaches based on structure engineering and composition engineering were then comprehensively discussed. Core-shell structure, heterogeneous interface and iron doping were proposed for stability enhancement. Various doping and composite methods were regarded as choices for improving electrical conductivity. To address the insufficient activating capability, element doping and template methods were considered as viable options. Finally, the perspectives of TMPs application in OER were outlined and the future research directions were highlighted.