A new insight into the promoting effects of transition metal phosphides in methanol electrooxidation

The construction of highly active catalysts for methanol oxidation reaction (MOR) is central to direct methanol fuel cells. Tremendous progress has been made in transition metal phosphides (TMPs) based catalysts. However, TMPs would be partially damaged and transformed into new substances (e.g., Pt-M-P composite, where M represents a second transition metal) during Pt deposition process. This would pose a large obstacle to the cognition of the real promoting effects of TMPs in MOR. Herein, Co2P co-catalysts (Pt-P/Co2[email protected], where NPC stands for N and P co-doped carbon) and Pt-Co-P composite catalysts (Pt-Co-P/NPC) were controllably synthesized. Electrocatalysis tests show that the Pt-Co-P/NPC exhibits superior MOR activity as high as 1016 mA/mgPt, significantly exceeding that of Pt-P/Co2[email protected] (345 mA/mgPt). This result indicates that the promoting effect is ascribed primarily to the resultant Pt-Co-P composite, in sharply contrast to previous viewpoint that Co2P itself improves the activity. Further mechanistic studies reveal that Pt-Co-P/NPC exhibits much stronger electron interaction and thus manifesting a remarkably weaker CO absorption than Pt-P/Co2[email protected] and Pt/C. Moreover, Pt-Co-P is also more capable of producing oxygen-containing adsorbate and thus accelerating the removal of surface-bonded CO*, ultimately boosting the MOR performance.