Hierarchical Porous Nickel Phosphide Electrode for Solar-Driven Green Hydrogen Production

To achieve the global "carbon neutral" goal and low-carbon economy by 2050-2100, hydrogen has been considered as an ideal renewable and sustainable energy carrier. As an abundant clean energy, solar energy can be utilized for the water splitting by the proper device and catalyst to produce green hydrogen without any pollution and carbon emission. For the purpose of PV-driven electrocatalytic water splitting, we propose a new hierarchical porous nickel phosphide (HPNP) electrode, which has a skeleton combined porous Ni₅P₄ nanocrystals on Ni foam. A facile fabrication approach is developed to achieve fine phase and morphology control of low-cost abundant materials (Ni, P) and scalable electrode manufacturing capability. The three-dimensional hierarchical structure of the Ni₅P₄@Ni foam includes nano pores ranging from 50-500 nm and micro pores ranging from 200-600 μm. The proposed HPNP catalyst facilitates the adequate exposure of the catalyst surface active sites to water, and the electrode wettability is systematically studied and tailored to further improve performance. As the result, our HPNP electrode exhibits exceptional electrocatalytic performance for the hydrogen evolution (HER, 145 mV), oxygen evolution (OER, 197 mV), and overall splitting potential (1.54 V) at 10 mA cm^-2 with 24 h stability. By combining a multi-junction PV cell with HPNP electrodes, our solar-driven standalone water splitting device can produce green hydrogen very efficiently.