Multifunctional nano-heterogeneous Ni(OH)₂/NiFe catalysts on silicon photoanode toward efficient water and urea oxidation

Exploiting inexhaustible free energy from the sun to produce clean and sustainable fuels is an attractive route toward the heavily polluted earth and energy shortage. Photoelectrochemical cell is strategic energy device because the generated fuels can be stored and used on-demand. Herein, we present the fabrication of Si photoelectrodes with efficient charge separation and transfer using metal-insulator-semiconductor heterostructures for energy-rich fuel production via photoelectrochemical water and urea oxidation. With controls of the native SiO_x insulator layer and catalytic NiFe metal layer, Si photoelectrode exhibits a photovoltage of 530 mV and a photocurrent density of 33.3 mA cm⁻² at 1.23 V versus reversible hydrogen electrode. Further employed Ni(OH)₂ catalysts allow Si photoanode to achieve fill factor of 25.73% and solar-to-hydrogen conversion efficiency of 10.8% with a perovskite/Si tandem solar cell. The fabricated Ni(OH)₂/NiFe/n-Si photoanode shows considerable performances toward urea oxidation. Our work presents new insights into sunlight-assisted hydrogen production using wastewater.