A simultaneous phosphorization and carbonization strategy to synthesize a defective Co₂P/doped-CNTs composite for bifunctional oxygen electrocatalysis

Integration of heteroatom doped carbon material and metal phosphide is an ideal strategy for bifunctional oxygen reduction and evolution catalysis. In this work, heteroatoms doped carbon nanotubes, together with cobalt phosphide (Co₂P/doped-CNTs) are prepared with a simultaneous phosphorization and carbonization strategy. It is revealed that the in-situ generated Co₂P weakens the catalytic graphitization effect of metallic Co during the carbonization process, thus bringing about large numbers of defects, which is conducive to generating more pyridinic-N species in the carbon nanotube. As a result, the ORR-active pyridinic-N species and the OER-active Co₂P are enriched in the carbon nanotube after the introduction of phosphorus, therefore providing dual active sites. The resultant Co₂P/doped-CNTs catalyst shows outstanding ORR and OER performances, which are comparable to those of the commercial counterparts. The bifunctional activity makes Co₂P/doped-CNTs an effective air–cathode catalyst for the rechargeable zinc-air batteries, showing a high power density and prominent cycling stability. This work abandons the traditional post-treatment phosphating method and realizes the integration of simplicity, safety and high efficiency.