Solar-Powered Water Electrolysis Using Thermally Annealed Nickel-Functionalized Multiwalled Carbon Nanotube-Based Bifunctional Electrodes for Green Hydrogen Production

Despite its environmentally benign nature and significant potential, hydrogen production via water electrolysis has not yet achieved widespread commercial adoption due to persistent challenges such as high system costs, suboptimal catalyst efficiency, and limited long-term durability. In this work, these limitations are addressed by developing a novel bifunctional electrocatalyst and integrating a self-sustained, low-cost energy input system for hydrogen generation through water electrolysis. The electrocatalyst was synthesized by functionalizing multiwalled carbon nanotubes (MWCNTs) via acid treatment, followed by nickel doping and a simple thermal annealing process at 450 °C for 3 h. The resulting material was subsequently cast onto nickel foam to fabricate the working electrode. X-ray diffraction analysis revealed that the functionalization and annealing processes promoted enhanced dispersion and surface coverage of Ni species, with the formation of crystalline cubic NiO phases and a hexagonal graphitic structure. Density functional theory analysis demonstrated that the synergistic effect of MWCNT functionalization and Ni deposition modulated the electronic structure, leading to an upshift of the d -band center. As a consequence, the developed electrode exhibited excellent bifunctional electrocatalytic activity, delivering Tafel slopes of 115.8 mV dec –1 and 98.73 mV dec –1 for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Long-term operational stability was confirmed by chronoamperometric measurements at 1.25 V for 105 h, showing negligible current decay. In the overall water-splitting reaction under alkaline conditions (pH 13.9), the electrolyzer achieved a current density of 10 mA cm –2 at a cell voltage of 1.63 V. The electrolysis system was powered by a 12 V battery charged using a 100 W solar panel, integrated with a locally fabricated power-management circuit board to regulate and maintain a constant current supply. The developed Ni-MWCNT-based bifunctional electrode coupled with a solar-powered electrolysis system demonstrates strong potential for sustainable, cost-effective green hydrogen production.