Electrochemical Synthesis of Nickel Hexacyanoferrate and Nickel Sulfide on Nickel Foam as Sustainable Electrocatalysts for Hydrogen Generation via Urea Electrolysis

A promising approach to energy-efficient hydrogen production is coupling the hydrogen evolution reaction (HER) with the urea oxidation reaction (UOR), significantly reducing the energy requirements. However, achieving a low-cost yet high-performance electrocatalyst for both HER and UOR remains challenging. Here, we present a facile method for synthesizing nanoporous nickel sulfide (NiS) and nickel hexacyanoferrate (NiHCF) nanocubes directly on nickel foam (NF) without any added nickel source using a cyclic voltammetry technique. In this approach, NF serves simultaneously as the substrate and nickel source, streamlining the synthesis process. The unique nanoarchitecture of NiHCF and NiS promotes highly efficient catalytic activity for both UOR and HER. NiHCF catalyzes urea oxidation by dual active sites of Ni and Fe with its synergistic interaction, without the formation of NiOOH or FeOOH. For hydrogen production, the self-supporting NiHCF/NF||NiS/NF-coupled system achieves a notably low cell voltage of 1.8 V at 100 mA cm^-2, which is approximately 487 mV lower than traditional IrO₂/NF||Pt/C/NF water electrolysis. This innovative electrochemical method enables the controlled synthesis of Ni-based nanoelectrocatalysts, offering a sustainable, energy-efficient pathway for H₂ production from urea-rich wastewater. This environmentally friendly strategy holds significant potential to reduce the global carbon footprint, paving the way for a greener future.