Optimizing metal geometrical structure of transition metal phosphides/P doped g-C3N4 enabling boosted water splitting

Abstract

Metal geometrical structure engineering of composite catalysts is powerful to boost their photocatalytic performance of hydrogen evolution. Herein, by rationally designing, transition metal phosphides (TMPs) have been loaded onto the P doped g-C3N4 (PCN) to construct catalysts TMPs/PCN. For the first time, the effect of geometrical structure of TMPs on the photocatalytic activity is optimized and a geometrical-site-dependent photocatalytic hydrogen evolution is experimentally determined. Tri-metallic FeCoNiP/PCN, having 59.6% occupancy of tetrahedral cobalt sites, gives hydrogen production rate of 205 μmol/g/h, better than that of mono-metallic (FeP, CoP, NiP), bi-metallic (FeCoP, CoNiP, FeNiP) TMPs/PCN, and even much superior to that of Pt/b-g-C3N4 and Pt/PCN. Trimetallic TMPs/PCN catalysts also show excellent OER performance. In addition to the efficient electron transfer between FeCoNiP and PCN, which can effectively improve the separation of photogenerated carriers, the high occupancy of tetrahedral cobalt sites of FeCoNiP as a co-catalyst promotes the formation of active intermediates, being the key to significantly improve the catalytic performance of ternary FeCoNiP/PCN. The findings in this work, especially about a link of the photocatalytic performance of TMPs/PCN composites and occupancy of tetrahedral cobalt site in co-catalysts TMPs, can open new occasion for creating novel composite catalysts and extending to other applications.