Biological upcycling of nickel and sulfate as electrocatalyst from electroplating wastewater

Upcycling nickel (Ni) to useful catalyst is an appealing route to realize low-carbon treatment of electroplating wastewater and simultaneously recovering Ni resource, but has been restricted by the needs for costly membranes or consumption of large amount of chemicals in the existing upcycling processes. Herein, a biological upcycling route for synchronous recovery of Ni and sulfate as electrocatalysts, with certain amount of ferric salt (Fe³⁺) added to tune the product composition, is proposed. Efficient biosynthesis of bio-NiFeS nanoparticles from electroplating wastewater was achieved by harnessing the sulfate reduction and metal detoxification ability of Desulfovibrio vulgaris. The optimal bio-NiFeS, after further annealing at 300 °C, served as an efficient oxygen evolution electrocatalyst, achieving a current density of 10 mA·cm^-1 at an overpotential of 247 mV and a Tafel slope of 60.2 mV·dec^-1. It exhibited comparable electrocatalytic activity with the chemically-synthesized counterparts and outperformed the commercial RuO₂. The feasibility of the biological upcycling approach for treating real Ni-containing electroplating wastewater was also demonstrated, achieving 99.5 % Ni²⁺removal and 41.0 % SO₄^2- removal and enabling low-cost fabrication of electrocatalyst. Our work paves a new path for sustainable treatment of Ni-containing wastewater and may inspire technology innovations in recycling/ removal of various metal ions.