Nanoengineered Bifunctional Porous Ni5P4 Electrocatalyst with Accelerated Bubble Departure and Reduced Overpotential for Solar-Driven Water Splitting

Abstract

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.1,2 The electrochemical conversion of solar energy to energy dense hydrogen fuel ensures a promising approach to generate a clean and sustainable source of energy.3,4 The integrated solar powered water electrolyzers for green hydrogen production completely eliminate all sources of carbon emissions arising from the direct power supply, towards achieving a low-carbon economy.5,6 However, large-scale solar water splitting for green hydrogen production still remains a challenge due to expensive electrocatalyst. As a low-cost, earth-abundant catalyst Nickel phosphide shows enormous potential to effectively reduce water and generate hydrogen. We propose a low-cost and facile approach to fabricate nanoengineered hierarchically porous Ni5P4 as an electrocatalyst (p-Ni5P4) providing high surface area and enabling fast gas diffusion. Nickel phosphide (p-Ni5P4@NF) has pores ranging from 50-500 nm to 200-600 μm and enlarges the electrochemically-active surface area by 5 times. The porous structure of p-Ni5P4@NF offers abundant cavities to gas nucleation and fast growth of H2 bubble, and small bubbles (10-50 µm) depart quickly owing to reduced contact line. By enhancing gas transfer and reducing bubble overpotential by 30%, p-Ni5P4@NF achieves excellent electrocatalytic performance with a low HER (145 mV), OER (197 mV) and overall water splitting potential (1.54 V) at 10 mA cm-2. Powered by multijunction PV cell, the full electrolytic cell records a high solar-to-hydrogen efficiency of 14.5 %. Keywords: Water splitting; Electrocatalysis; Green Hydrogen; Nickel Phosphide.