Crystalline Copper Phosphide Nanosheets as an Efficient Janus Catalyst for Overall Water Splitting

Hydrogen is essential to many industrial processes and could play an important role as an ideal clean energy carrier for future energy supply. Herein, we report for the first time the growth of crystalline Cu₃P phosphide nanosheets on conductive nickel foam (Cu₃P@NF) for electrocatalytic and visible light-driven overall water splitting. Our results show that the Cu₃P@NF electrode can be used as an efficient Janus catalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). For OER catalysis, a current density of 10 mA/cm² requires an overpotential of only ∼320 mV and the slope of the Tafel plot is as low as 54 mV/dec in 1.0 M KOH. For HER catalysis, the overpotential is only ∼105 mV to achieve a catalytic current density of 10 mA cm^-2. Moreover, overall water splitting can be achieved in a water electrolyzer based on the Cu₃P@NF electrode, which showed a catalytic current density of 10 mA/cm² under an applied voltage of ∼1.67 V. The same current density can also be obtained using a silicon solar cell under ∼1.70 V for both the HER and the OER. This new Janus Cu₃P@NF electrode is made of inexpensive and nonprecious metal-based materials, which opens new possibilities based on copper to exploit overall water splitting for hydrogen production. To the best of our knowledge, such high performance of a copper-based water oxidation and overall water splitting catalyst has not been reported to date.