Sustainable Synthesis of Ni-Biochar Catalysts from Agro-Industrial Residues for Hydrogen Generation via NaBH₄ Hydrolysis

The development of sustainable, low-cost catalysts for on-demand hydrogen generation is essential. In this work, nickel-impregnated biochar catalysts derived from agro-industrial biomass residues are synthesized via a sustainable waste-assisted impregnation strategy and evaluated for hydrogen generation via sodium borohydride hydrolysis. Different agro-industrial biochar matrices were investigated to evaluate the influence of biomass-derived surface chemistry and porosity on nickel dispersion and hydrogen-generation performance, using a concentrate recovered from the spent liquor of hydrothermal carbonization. This concentrate served as a stabilizing agent under mild conditions. Fast hydrogen-sensor-based screening enabled identification of the most active catalyst, which was subsequently evaluated by volumetric hydrogen-generation measurements. The best-performing material, based on a biochar (inner husk of Jatropha fruit) impregnated with nickel, exhibited a hydrogen generation rate of 118 mL·min⁻¹·g⁻¹ at room temperature and a reduced activation energy of 51 kJ·mol⁻¹ compared to uncatalyzed hydrolysis. Structural and textural characterization revealed that the improved catalytic performance is attributable to the combined influence of accessible metallic domains, a mineral-rich surface, and a well-developed micro-mesoporous structure. Reusability tests demonstrated good catalytic stability after an initial activation cycle. These findings demonstrate the potential of waste-derived biochar materials as sustainable support for efficient Ni catalysts for environmentally friendly hydrogen production.