Integrated Valorization of Sargassum spp. into Ni/Biochar Electrocatalysts for Alkaline Oxygen Reduction

Developing sustainable and low-cost electrocatalysts is important to reduce platinum dependence in alkaline fuel cells and support green hydrogen technologies. In this work, nickel nanoparticles (NiNPs) were synthesized through a green route using aqueous extracts of Sargassum spp. as reducing and stabilizing agents. The residual biomass was subsequently converted into activated biochar (BC) by KOH activation and pyrolysis at 700 °C, yielding a porous carbon support with a BET surface area of 1935 m2 g−1. Ni/BC electrocatalysts with nominal nickel loadings of 3, 5, 10, and 20 wt% were prepared and denoted BC–Ni3, BC–Ni5, BC–Ni10, and BC–Ni20. Physicochemical characterization confirmed the formation of Ni-based nanoparticles, graphitic carbon domains, and surface oxygen/nitrogen functionalities. Electrochemical evaluation in 0.1 M KOH showed that ORR performance depended on Ni loading. Among the Ni-based catalysts, BC–Ni20 delivered the highest current density (1.64 mA cm−2 at 0.2 V vs. RHE), the most positive half-wave potential (0.67 V vs. RHE), and good durability after 5000 accelerated degradation cycles, with limited losses in onset and half-wave potentials. Although 10% Pt/Vulcan exhibited higher overall activity, the results demonstrate that Sargassum-derived Ni/biochar materials are promising platinum-group-metal-free electrocatalysts, offering a feasible route for biomass valorization and sustainable energy conversion.