Synthesis of Ni-P alloy coatings by pulsed electrodeposition: the effect of additive content on morphology, local structure and electrochemical properties for HER

Abstract Alloy coatings based on nickel and phosphorus (NiP) have shown encouraging electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in alkaline conditions. The NiP electrocatalyst offers several advantages over other HER catalysts, including its high activity, stability, abundance, and affordability. The purpose of this study is to determine whether concentration differences of the NH 4 Cl additive during electrodeposition affect the physical, chemical, and electrochemical properties of the Ni-P alloy deposits. For this purpose, three distinct Ni-P coatings (NP02, NP1, and NP3) are synthesized by electrodeposition using three different concentrations of ammonium chloride (0.2 M, 1 M, and 3 M) in an electrochemical bath also comprising nickel sulfate and sodium hypophosphite. Utilizing powder XRD, AFM, XANES, EXAFS, and SEM-EDX techniques, the synthesized Ni-P coating’s crystal structure, texture, local structure, composition and morphology are analysed. As we moved from NP02 to NP3, the surface texture smoothened, particle size distribution improved, an orderly rise in P-content was observed, the co-ordination number of Ni for the Ni-P bond progressively escalated, and all these led to a gradual increase in their electrocatalytic activity for HER in alkaline media, with NP3 exhibiting the minimum charge transfer resistance and Tafel slope of 53.9 mV dec − 1 . Electrodeposition studies using in-situ UV-visible spectroscopic methods show significant variations in the deposition mechanism when the NH 4 Cl content is altered. Therefore, by adjusting only the additive content in the electrodeposition bath during the synthesis of Ni-P alloy coatings, their P-content, topography, morphology, and local structure can be suitably regulated, consequently favorably tailoring their electrocatalytic activities for HER.