Biogenic synthesis of the mixed-valence FexOy/g-CN electrocatalyst using coiled flow inverter for green hydrogen evolution

The development of earth-abundant and cost-effective electrocatalysts for hydrogen evolution reaction (HER) is ciritcal for advancing green hydrogen production. In this study, we report the green synthesis of the mixed-valence Fe_xO_y nanoparticle (NP)-doped g-CN (Fe_xO_y/g-CN) electrocatalyst using a coiled flow inverter (CFI) reactor. The Fe_xO_y NPs, including Fe₂O₃, and Fe₃O₄, are synthesized using an aqueous green tea extract, which serves as a biogenic reducing and stabilizing agent. The CFI-assisted synthesis enables uniform dispersion, good control over Fe-loading in the catalyst, and high-throughput production, overcoming the limitations of conventional batch processes. A comprehensive morphological, physicochemical, and electrochemical characterization of the synthesized electrocatalyst confirms the enhanced conductivity, active site density, and stability of the material. The electrocatalyst exhibits an HER overpotential of 256 mV at 10 mA cm^-2, Tafel slope of 154 mV dec^‑1, and excellent long-term stability over 24 h in 1 M KOH electrolyte. These improvements are attributed to the synergistic effects of the mixed-valence Fe_xO_y species and the conductive g-CN matrix, which enhance charge transfer and electron mobility. This study pitches the biogenic Fe_xO_y/g-CN electrocatalyst as a sustainable alternative to noble metal-based catalysts, contributing to the present global transition towards the scalable green hydrogen production.