Nickel Electrocatalysts Obtained by Pulsed Current Electrodeposition from Watts and Citrate Baths for Enhanced...

Efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media are essential for sustainable hydrogen production. In this study, Ni electrocatalysts were deposited on pencil graphite using a simple one-step pulsed current electrodeposition method, from both acidic Watts and alkaline citrate baths. The influence of bath type and electrodeposition parameters-current density and temperature-on catalyst morphology and performance for HER was systematically investigated by scanning electron microscopy and electrochemical methods. Linear sweep voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy (EIS) were used to evaluate the electrocatalytic activity, stability, and HER mechanism. The best catalytic performance was achieved for the Ni electrocatalyst deposited from the citrate bath at 50 mA cm^-2 and 40 °C, showing an exchange current density of 0.93 mA cm^-2, a Tafel slope of -208 mV dec^-1, and overpotentials of -210 mV and -386 mV at 10 and 100 mA cm^-2, respectively, in 1 M KOH solution. Chronopotentiometry confirmed improved stability and an overpotential reduction of approximately 92 mV as compared to pure Ni, while EIS revealed the lowest charge transfer resistance. It was shown that the electrocatalysts deposited from the citrate bath outperform those from the Watts bath, and electrodeposition at 40 °C is optimal for achieving the highest electrocatalytic activity for HER.