Enhancing hydrogen generation through urea electro-oxidation on a bimetallic and dual-anionic NiFeSP/NF nanostructured electrode

Abstract

Besides reducing pollution and removing urea from wastewater, electro-oxidation of urea has also offered new prospects for filling the overall water gap for economically producing hydrogen. In this regard, a simple and low-cost electrochemical deposition technique was used to prepare a highly efficient bifunctional electrocatalyst for the HER and the UOR (in place of the OER) on nickel foam (NiFeSP/NF). A three-dimensional and nanoporous NiFeSP/NF electrocatalyst demonstrated relatively high stability and electrocatalytic activity. Notably, the bimetallic and dual-anionic NiFeSP/NF electrode demonstrated good performance for the HER (42, 111 and 138 mV at current densities of −10, −100, and −200 mA cm⁻², respectively), the OER (1.451, 1.502, 1.528, and 1.576 V vs. RHE at 10, 100, 200 and 400 mA cm⁻², respectively), and the UOR (1.304, 1.346, 1.389 and 1.473 V vs. RHE at current densities of 10, 100, 200 and 400 mA cm⁻², respectively). Moreover, the use of a NiFeSP/NF||NiFeSP/NF pair as an anode and a cathode in an overall water-splitting system assisted by urea achieved 1.348 and 1.582 V vs. RHE at 10 and 100 mA cm⁻² in 1.0 M KOH with 0.33 M urea solution, which are 163 and 234 mV lower than those achieved in 1.0 M KOH alkaline solution, respectively. Additionally, the NiFeSP/NF||NiFeSP/NF pair demonstrates long-term stability (30 h) in a chronopotentiometry test at 100 mA cm⁻² in 1.0 M KOH with 0.33 M urea solution. This bimetallic and dual-anionic NiFeSP electrode exhibits substantial catalytic activity due to the appropriate synergy between Fe and Ni, the modification of the electronic structure enabled by the dual anions, and the enhanced electrocatalytically active surface caused by high porosity. The low cost and single-step manufacturing method of the NiFeSP electrode, high electrocatalytic activity, and stability make it potentially ideal for commercial use in hydrogen generation and treatment of wastewater containing urea.