Substituting Wastewater Effluent for High-Grade Water in Alkaline Water Electrolysis Using Hafnium-Based Transition Metal Electrocatalysts

Green hydrogen is a key technology for achieving carbon neutrality. A genuinely sustainable hydrogen production process must consider not only energy inputs but also water and material resources, yet most research focuses primarily on energy. Here, we present a promising method for green hydrogen production that utilizes wastewater, addressing broader sustainability challenges and conserving freshwater for drinking and sanitation. We investigated the use of a transition metal-based HfNi-WO 3 @NF electrocatalyst for green hydrogen production from wastewater. The proposed electrocatalyst exhibits excellent performance for hydrogen and oxygen evolution. Deionized water (DI), tertiary effluent (TE), and secondary effluents (SE1 and SE2) in 1 M KOH require only 1.52, 1.57, 1.58, and 1.60 V, respectively, to reach a current density of 10 mA/cm 2 . Impressively, the electrocatalyst achieves a high current density of 1 A/cm 2 at just 1.91 V for TE, while maintaining exceptional stability over 200 h, with a nominal degradation of 0.678 mV/h, demonstrating excellent active, durable performance of the electrocatalyst under complex wastewater conditions. By replacing high-purity water with wastewater sources, this approach opens new opportunities to develop a sustainable hydrogen economy and advance water management strategies.