Electrochemical semi-sacrificial growth of a self-supporting MOF-based electrode for urea electrooxidation-coupled water electrolysis

Abstract

Replacing the anodic oxygen evolution reaction in water electrolysis with thermodynamically more favorable oxidation reactions is appealing for reducing the energy consumption of hydrogen production but is limited by the lack of efficient yet cost-effective electrodes. Herein, a self-supporting NiFe-based Prussian blue analogue (PBA) electrode (NiFe-PBA-NF) was directly prepared via a facile semi-sacrificial anodic electrodeposition strategy, in which ultrasmall NiFe-PBA nanoparticles were grown uniformly and compactly on the nickel foam (NF) surface. Benefiting from its ingenious structure and the synergistic effect between Ni and Fe sites, the as-prepared NiFe-PBA-NF exhibited excellent electrochemical performance in the urea oxidation reaction (UOR) with a required potential of only 1.375 V to deliver a current density of 100 mA cm⁻², outperforming the powdered NiFe-PBA and even the commercial RuO₂ catalyst. Moreover, a Ru-NiFe-PBA-NF electrode assembled with ultrathin Ru-doped NiFe-PBA nanosheets was fabricated through further Ru-modification treatment, which exhibited a remarkable electrochemical performance in the hydrogen evolution reaction (HER), even better than that of the commercial Pt/C catalyst. Ultimately, a UOR-coupled energy-saving hybrid water electrolysis system was constructed by employing Ru-NiFe-PBA-NF and NiFe-PBA-NF as the electrodes for the cathodic HER and anodic UOR, respectively, which only requires a cell voltage of 1.36 V to deliver a current density of 10 mA cm⁻², far superior to a conventional water electrolysis system. This work provides a novel way to design advanced organic–inorganic hybrid-based electrodes and innovative water electrolysis systems for efficient hydrogen production.