Noble Metal Phosphides Supported on CoNi Metaphosphate for Efficient Overall Water Splitting.

ABSTRACT

Transition metal metaphosphates and noble metal phosphides prepared under similar conditions are potential hybrid catalysts for electrocatalytic water splitting, which is of great significance for H2 production. Herein, the structure and electrocatalytic activity of different noble metal species (i.e., Rh, Pd, Ir) on CoNiP4O12 nanoarrays have been systematically studied. Due to the different formation energies of noble metal phosphides, the phosphides of Rh (RhPx) and Pd (PdPx) as well as the noble metal Ir are obtained under the same phosphorylation conditions perspectively. RhPx/CoNiP4O12 and PdPx/CoNiP4O12 exhibit much better HER activity than Ir/CoNiP4O12 due to the advantages of phosphides. Density functional theory (DFT) calculations reveal that the extraordinary activity of RhPx/CoNiP4O12 originated from the strong affinity to H2O and optimal adsorption for H*. The best RhPx/CoNiP4O12 only requires a low overpotential of 30 and 234 mV to deliver 10 mA cm-2 for HER and OER, respectively, and therefore is effective for overall water splitting (requiring 1.57 V to achieve a current density of 10 mA cm-2). This work not only develops a novel RhPx/CoNiP4O12 electrocatalyst for overall water splitting but also provides deep insight into the formation mechanism of noble metal phosphides.