Wastewater to hydrogen: iron–nickel electrocatalysts fabricated by a green synthesis achieving industrial current densities

Abstract

The development of sustainable hydrogen production technologies is crucial to address the global energy crisis and reduce carbon emissions. With growing concerns over freshwater scarcity, the combination of green hydrogen production with ammonia oxidation reaction from wastewater, emerges as a highly promising strategy for meeting carbon goals and reusing treated water. Here, we report a green, scalable, room-temperature chemical reduction method for the successful synthesis of self-supported FeNiB, FeNiBP, and FeNiP electrocatalysts on nickel foams. FeNiB@NF exhibited the highest HER activity, achieving −469 mA cm⁻² at −0.71 V vs. RHE with an overpotential of −0.26 V vs. RHE at −100 mA cm⁻² in alkaline water and −330 mA cm⁻² at −0.69 V vs. RHE and with an overpotential of −0.34 V vs. RHE at −100 mA cm⁻² in ammonia-rich electrolyte, while FeNiBP@NF delivered superior OER performance of 972 mA cm⁻² at 2.3 V vs. RHE and AOR performance of 963 mA cm⁻² at 1.97 V vs. RHE. Physicochemical analysis further revealed that the strong reducing power of sodium borohydride was crucial in generating metallic Fe and Ni states, underpinning the outstanding activity of FeNiB@NF in HER. On the other hand, the synergistic effects of boron and phosphorus in FeNiBP@NF likely facilitated OH* and NH₃* adsorption, contributing towards its high catalytic activity in OER and AOR, respectively.