Nickel occupies a privileged position among non-precious metals for the hydrogen evolution reaction, the cathodic half-reaction that produces molecular hydrogen from water. Its electronic structure places it near the top of the volcano plot relating exchange current density to hydrogen binding energy, meaning it adsorbs hydrogen atoms with nearly ideal strength, close to the thermoneutral condition demanded by Sabatier’s principle. Nickel is also inexpensive and reasonably corrosion-resistant in both acidic and alkaline media. Previous work has shown that alloying nickel with cobalt, molybdenum, or iron can slash the overpotential required to drive meaningful current densities, but such multi-component catalysts typically demand complex synthesis routes that are difficult to integrate into continuous electrode manufacturing.

The Indian team chose a different path. They used a Watt’s bath, the workhorse formulation of industrial nickel electroplating, containing nickel sulfate, nickel chloride, and boric acid at a pH of 3.64. The substrate was titanium foil, chemically etched in a sulfuric-nitric acid mixture to strip away the native oxide layer and expose a rough, oxide-free metallic surface studded with step-edge nucleation sites. Titanium is an underutilized but compelling support: its stable native oxide resists corrosion across the full pH range, its rigidity allows precise geometric area definition for accurate benchmarking, and it is already the material of choice for bipolar plates and current collectors in proton exchange membrane electrolysers. By contrast, the nickel foam, stainless steel, and carbon cloth substrates common in the literature each suffer from oxidation, passivation, or poor adhesion under operating conditions.

The optimization proceeded in three stages. First, the team varied the deposition current density from minus one to minus fifty milliamperes per square centimeter at a fixed sixty-second deposition time. Scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that nickel content climbed monotonically with current density, reaching roughly ninety-six weight percent at the highest current. But loading alone proved a poor predictor of performance. At the lowest current, deposits were discontinuous islands with large gaps and poor electrical connectivity. At minus ten milliamperes per square centimeter, a kinetically balanced regime emerged in which nucleation, growth, and competing hydrogen evolution at the cathode proceeded at comparable rates, producing compact, fine-grained particles threaded with nanoscale voids. These voids, far from being defects, are templates left behind by hydrogen bubbles that nucleated on the growing surface and later detached.

The high-current electrodes told a cautionary tale. Despite their heavy nickel loading, coatings deposited at minus twenty-five and minus fifty milliamperes per square centimeter chipped, flaked, and delaminated during hydrogen evolution testing, a failure the authors attribute to compressive stress from lattice mismatch, trapped hydrogen, and supersaturated growth. The lesson is counterintuitive but practically important: maximizing catalyst loading is not a viable strategy, and the optimal compromise sits at moderate current density, where the electrode achieved an overpotential of 148 millivolts at ten milliamperes per square centimeter in sulfuric acid.

The second stage held the total deposited charge constant at 0.6 coulombs per square centimeter while varying deposition time from thirty to one hundred eighty seconds, thereby decoupling morphology from loading. The deposits followed a Volmer-Weber three-dimensional island growth mode, driven by the large lattice mismatch and weak adhesion between nickel and titanium. Short depositions produced a burst of tiny nuclei around 160 nanometers in a near-continuous film with few open voids. At one hundred twenty seconds, the growth-dominated regime took over, particles coarsened to about 307 nanometers, and the film achieved the sweet spot: full electrical connectivity with a preserved network of interparticle voids for electrolyte access. The overpotential dropped to 143 millivolts, a 56-millivolt improvement over the thirty-second electrode, while extending to one hundred eighty seconds brought no further benefit as voids began to close.

The third and most striking stage replaced continuous current with pulsed galvanostatic deposition. The total on-time of one hundred twenty seconds was split into one, four, eight, or twelve equal pulses separated by thirty-second open-circuit rests. During each rest interval, two things happen: nickel ions depleted at the cathode diffuse back from the bulk, resetting the concentration before the next pulse, and adherent hydrogen bubbles detach from the surface, eliminating the large voids and discontinuities they would otherwise imprint. Single-pulse deposition yielded a thick, featureless film. Eight pulses produced the morphological optimum, with uniformly distributed particles, the narrowest size distribution, and a regular, well-connected void network. Twelve pulses tipped into coalescence, as overly short pulses allowed adjacent nuclei to merge before the next interruption. X-ray diffraction confirmed the deposits were purely metallic nickel, with a contracted lattice parameter of 3.494 angstroms versus the bulk value of 3.524, evidence of in-plane compressive stress inherited from the nickel-titanium interface.

Electrochemical impedance spectroscopy quantified the kinetic gains. Bare titanium is essentially inert toward hydrogen evolution, with a charge-transfer resistance near 9.08 times ten to the fourth ohms per square centimeter; even a suboptimal nickel film dropped that figure by more than an order of magnitude. Interestingly, the electrode with the largest electrochemically active surface area, the four-pulse sample, was not the best catalyst. Its fine, well-separated particles created interparticle electrical resistance. The eight-pulse electrode, with better-connected particles and lower charge-transfer resistance, struck the superior balance between site accessibility and conductivity, a reminder that surface area alone does not determine electrocatalytic performance.

Across all three electrolytes, the optimized electrode outperformed bare titanium. In 0.5 molar sulfuric acid it delivered a Tafel slope of 149 plus or minus 3 millivolts per decade, and in 1 molar potassium hydroxide a nearly identical 151 plus or minus 4, values consistent with a Volmer-Heyrovsky mechanism in which the desorption step is partially rate-limiting. The near-identical acid and alkaline slopes suggest a common dominant rate-determining step across both media. In neutral phosphate-buffered saline, kinetics deteriorated sharply, with a Tafel slope of 329 plus or minus 18 millivolts per decade reflecting mass-transport limitations, low proton activity, high solution resistance, and competitive phosphate adsorption, yet the nickel coating still beat bare titanium. Stability tests showed negligible drift in acid over three-hour holds at current densities up to minus one hundred milliamperes per square centimeter, with the potential actually improving by about sixty millivolts at the highest current, indicating in-situ activation rather than degradation. Post-operation X-ray diffraction revealed titanium hydride formation in the substrate, evidence that atomic hydrogen diffuses into the titanium under sustained cathodic polarization, but no catalytically deleterious nickel hydroxide or hydride phases.

The most consequential benchmark came against a commercial nickel mesh. Run side by side at minus fifty milliamperes per square centimeter in sulfuric acid for eighteen hours, the pulse-deposited planar electrode initially lagged slightly behind the three-dimensional mesh, whose hierarchical porosity offers greater active area and faster bubble release. But after an activation period of wetting and surface restructuring, it stabilized at a potential comparable to the commercial product, with neither electrode showing measurable degradation. For the authors, this validates the central thesis: catalytic performance is limited not by the quantity of nickel but by the quality and accessibility of the active surface. A simple Watt’s bath, an eight-pulse protocol, and a planar titanium foil, all processed at room temperature with earth-abundant materials, can rival a commercial electrode. As emerging electrolyser architectures, from seawater splitters to decoupled water-splitting devices, demand catalysts that survive near-neutral conditions, careful process engineering of the deposition step may prove as important as catalyst chemistry itself.

Subject of Research: Pulse electrodeposition of nickel coatings on titanium for pH-universal hydrogen evolution electrocatalysis

Article Title: Pulse electrodeposition of Ni on Ti substrates for hydrogen evolution across acidic, alkaline, and neutral electrolytes

Article References: Kandwal, A., Choudhary, V., Tyagi, A., Konathala, S. K., Prakashaiah, B. G., Sinha, A. K., & Dhiman, M. (2026). Pulse electrodeposition of Ni on Ti substrates for hydrogen evolution across acidic, alkaline, and neutral electrolytes. Discover Electrochemistry, 3(1), Article 61. https://doi.org/10.1007/s44373-026-00149-8

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00149-8

Keywords: hydrogen evolution reaction, nickel electrodeposition, pulsed deposition, titanium substrate, electrocatalysis, green hydrogen, water electrolysis, Tafel analysis, nanostructured electrodes, electrochemical impedance spectroscopy, earth-abundant catalysts, Watt's bath