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

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 (RhP_x) and Pd (PdP_x) as well as the noble metal Ir are obtained under the same phosphorylation conditions perspectively. RhP_x/CoNiP₄O₁₂ and PdP_x/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 RhP_x/CoNiP₄O₁₂ originated from the strong affinity to H₂O and optimal adsorption for H*. The best RhP_x/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 RhP_x/CoNiP₄O₁₂ electrocatalyst for overall water splitting but also provides deep insight into the formation mechanism of noble metal phosphides.