In situ decorated Cu₂FeSnS₄ nanosheet arrays for low voltage hydrogen production through the ammonia oxidation reaction

Water electrolysis is a possible method for producing ultrapure hydrogen (H₂). However, the typical water electrolysis process has significant overpotential, mostly because of the slow kinetics in the oxygen evolution reaction (OER). The OER that produces reactive oxygen species weakens the proton exchange membrane in the water electrolyzer. Besides, oxygen can interact with cathodic H₂ to create explosive gaseous mixtures. These issues can be solved using the hybrid water electrolysis (HWE) method, replacing the OER with an alternative oxidation reaction. The oxidizing chemical agent helps in electrochemical hydrogen production at extremely low voltage while oxidizing the substance to value-added products in the HWE process. Electrocatalysts are used to power the chemical species-assisted hydrogen generation in the HWE process. Quaternary metal sulfide, a highly electrochemically active material, has attracted attention as a promising platform for effective application in various redox reactions. In this work, we reported quaternary copper-iron-tin sulfide with the chemical formula Cu₂FeSnS₄ (CFTS) in the form of nanosheets and evaluated the HWE with the ammonia oxidation reaction at the anode. The CFTS nanosheets were synthesized by a facile one-step solvothermal method using carbon cloth (CC) as the substrate. To evaluate the effect of solvents used in the synthesis process on the morphology and electrochemical performance of the material, deionized water (DI), ethanol (EtOH), and ethylene glycol (EG) were applied, and their effects were studied thoroughly. A feasible formation mechanism has been presented in which the viscosity and dielectric constants of the solvents play key roles in determining the morphology of CFTS nanosheets. The CFTS nanosheets synthesized in EG showed a porous and rougher surface than those produced using other solvents. As expected, the EG-mediated CFTS exhibited remarkable H₂ production with ammonia oxidation at the anode due to better electron and electrolyte ion transmission. Our results describe the effect of solvents used for solvothermal reactions and that the CFTS material can be deliberated as a potential alternative for divergent energy conversion device applications.