Turning Fe-Rich Waste into an Advanced Electrocatalyst for the Production of H ₂ and Useful Carboxylates

In this study, discarded bike tire rim wires composed primarily of iron (Fe) were repurposed into electrocatalysts through a corrosion-assisted surface activation strategy. The wires were acid-treated, heat-cleaned, and then subjected to a 10-day corrosion process in a NaOH and Ca-(OCl)₂ solution. Their catalytic activities toward the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and small-molecule oxidation (such as methanol, ethanol, and urea) were systematically evaluated. Optimal HER and OER performances were observed on the eighth and third days of activation, respectively, reflecting their distinct mechanistic pathways in alkaline media. Tafel and electrochemical impedance spectroscopy revealed that both intrinsic catalytic properties and surface area enhancements contributed to activity improvements. The repurposed Fe-rich electrodes exhibited high selectivity for the controlled oxidation of methanol and ethanol into carboxylic acids, which is attributed to their weak OH adsorption. Remarkably, urea oxidation occurred at significantly lower potentials, likely due to favorable Fe-NH₂ interactions. Surface and compositional analyses confirmed that the wires were composed of 99.76% Fe, with trace amounts of Cr and Ni. This work highlights the potential of transforming metallic waste into functional electrocatalysts, offering a dual benefit of sustainable resource utilization and mechanistic insights for water electrolysis and wastewater valorization applications.