Porous CoP coating on stainless steel: Application as an electrocatalyst for acidic hydrogen evolution reaction

The development of new catalysts for the acidic hydrogen evolution reaction with both reasonable activity and stability is crucial to reducing the cost of PEM electrolyzers and promoting their widespread commercialization. In this study, we present a straightforward electrodeposition method for coating of CoP electrocatalyst on a stainless steel substrate as a Pt-free alternative catalyst electrode for the acidic hydrogen evolution reaction (HER). Based on field emission scanning electron microscopy (FE-SEM) analysis, varying the concentration of phosphorus has a substantial effect on the morphological features of the deposit. At lower phosphorus concentrations, the deposit has a smooth and porous structure. As the phosphorus concentration increases, the surface structure becomes gradually rough while maintaining a high level of porosity. The structural and compositional characteristics of the catalysts have been examined using X-ray diffraction (XRD), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) analyses. The electrocatalytic activity of the prepared catalysts was evaluated by electrochemical techniques. The elevated roughness was advantageous in achieving a greater electrochemical surface area resulting in high electrocatalytic activity. The optimized coated electrode exhibited the highest electrocatalytic activity, resulting in lower overpotential values of 128 ± 1.2 mV, 163 ± 2.6 mV, and 181 ± 4.3 mV at current densities of 10, 50, and 100 mA cm⁻², respectively. The CoP coated electrode demonstrated exceptional stability based on the chronopotentiometric measurements conducted over a period of 25 h at three distinct current densities of 10, 50, and 100 mA cm⁻² and 100 h at 100 mA cm⁻². These findings pave the way to investigate the use of non-precious metallic phosphide coated stainless steel as cathode electrocatalysts for hydrogen production by proton exchange membrane (PEM) water electrolyzers.