Facile synthesis of α/β-FeOOH-based self-supported hierarchical electrocatalysts on arbitrary metal substrates for efficient and hyper-stable HER, OER, UOR, and overall water splitting: A general strategy

Abstract

Slow kinetics of the oxygen evolution reaction (OER) during water electrolysis limits hydrogen evolution reaction (HER) efficiency. Urea oxidation reaction (UOR), with a lower thermodynamic potential (0.37 V vs. RHE) than OER, offers an energy-saving alternative. Designing robust, multifunctional electrocatalysts for hydrogen generation by water electrolysis remains challenging. In this work, a universal two-stage solvothermal strategy was developed to synthesize α/β-FeOOH-based self-supported hierarchical structure catalysts on arbitrary metal substrates, evading polymeric binders. FeOOH/Fe achieves exceptional HER performance, while FeOOH/Ni delivers superior OER/UOR activity, exhibiting extremely-low UOR kinetics with a 12.24 mV·dec⁻¹ Tafel slope. Asymmetric FeOOH/Ni (+)||FeOOH/Fe (−) electrolyzer requires ultralow voltages of 1.799 V (1.0 M KOH), 1.888 V (seawater/1.0 M KOH), and 1.627 V (0.33 M urea/1.0 M KOH) to drive 300 mA cm⁻², surpassing most similar systems. It maintains >9 Faraday efficiency over 100-h at ≥ 300 mA cm⁻², demonstrating industrial-grade stability. The catalysts’ accessible active sites, accelerated charge transfer, rapid kinetics, and superhydrophilicity synergistically enable rapid mass/electron transport and durable operation. This work provides a scalable platform for binder-free electrocatalysts, advancing practical hydrogen production through urea-assisted electrolysis and seawater utilization.