An Efficient Cobalt Phosphide Electrocatalyst Derived from Cobalt Phosphonate Complex for All-pH Hydrogen Evolution Reaction and Overall Water Splitting in Alkaline Solution.

The development of low-cost and highly efficient electrocatalysts via an eco-friendly synthetic method is of great significance for future renewable energy storage and conversion systems. Herein, cobalt phosphides confined in porous P-doped carbon materials (Co-P@PC) are fabricated by calcinating the cobalt-phosphonate complex formed between 1-hydroxyethylidenediphosphonic acid and Co(NO3 )2 in alkaline solution. The P-containing ligand in the complex acts as the carbon source as well as in situ phosphorizing agent for the formation of cobalt phosphides and doping P element into carbon material upon calcination. The Co-P@PC exhibits high activity for all-pH hydrogen evolution reaction (overpotentials of 72, 85, and 76 mV in acidic, neutral, and alkaline solutions at the current density of 10 mA cm-2 ) and oxygen evolution reaction in alkaline solution (an overpotential of 280 mV at the current density of 10 mA cm-2 ). The alkaline electrolyzer assembled from the Co-P@PC electrodes delivers the current density of 10 mA cm-2 at the voltage of 1.60 V with a durability of 60 h. The excellent activity and long-term stability of the Co-P@PC derives from the synergistic effect between the active cobalt phosphides and the porous P-doped carbon matrix.