Tailoring porous Ni–Co alloy structures via dynamic hydrogen bubble templating (DHBT) using a design of experiments approach

Porous metallic coatings are of significant interest for electrochemical applications due to their high specific surface area and abundant active sites. Among them, nickel–cobalt (Ni–Co) alloy coatings offer attractive electrochemical properties and tunability through compositional control. In this study, porous Ni–Co alloy structures were fabricated using the dynamic hydrogen bubble templating (DHBT) method, and the effects of key process parameters on their microstructural and electrochemical responses were systematically investigated. Porous coatings were electrodeposited from an acidic chloride-based electrolyte containing nickel and cobalt salts. A response surface methodology based on a central composite design was employed to evaluate the influence of two independent variables: electroplating current density (300–500 mA.cm -2 ) and cobalt content in the electrolyte (25–75 at. %). The responses included pore diameter, pore density, and double-layer capacitance (C dl ). Surface morphology and composition were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy, while pore characteristics were quantified through image analysis. The electrochemical response was assessed by cyclic voltammetry (CV) in 1 M KOH to determine C dl and linear sweep voltammetry (LSV) for HER and OER performances. The results demonstrate that the DHBT method successfully fabricated interconnected honeycomb-like porous Ni–Co structures through dendritic growth around dynamically generated hydrogen bubbles. Statistical analysis revealed that pore diameter is primarily governed by the nonlinear effects of current density and cobalt content, indicating the presence of an optimal processing window. Pore density is mainly controlled by the nonlinear behavior of current density, with cobalt content exerting a secondary influence. In contrast, the double-layer capacitance is predominantly controlled by the cobalt content of the coating and exhibits a nonlinear response, with maximum C dl achieved at the high cobalt content and current density. Optimal processing conditions were identified at a current density of 490 mA.cm -2 and a cobalt content of approximately 70 at. %, yielding porous structures with enhanced structural and electrochemical performance. The optimized DHBT-fabricated Ni–Co porous coating (70 at. % Co) delivers exceptional bifunctional electrocatalytic performance, with HER and OER overpotentials of only 56 mV and 268 mV at 10 mA.cm -2 , respectively, directly correlating with cobalt-induced structural refinement.