Metal–Organic Framework-Derived Fe/Co-based Bifunctional Electrode for H₂ Production through Water and Urea Electrolysis

Hollow-structured Fe_xCo_2−xP, Fe_xCo_3−xO₄, and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal–organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fe_xCo_2−xP/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm⁻² respectively, whereas Fe_xCo_3−xO₄/NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fe_xCo_2−xP/NF requires only 1.61 V to obtain 10 mA cm⁻². In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fe_xCo_2−xP/NF anode needs just 1.345 V to achieve 20 mA cm⁻², which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H₂ through urea electrolysis needs only 1.42 V to drive 10 mA cm⁻².