Nanoparticle-Mediated Waste Valorization: Transforming Heavy Metal Pollutants into Efficient Electrocatalysts for Methanol Oxidation

Abstract

This study demonstrates a waste-to-catalyst strategy in which nickel ferrite (NFO) first removes Cu(II), Co(II), and Cd(II) from aqueous solutions, and the resulting metal-loaded ferrites are subsequently employed as non-noble-metal electrodes for alkaline methanol oxidation. Pristine NFO achieved removal efficiencies of 74.5% for Cu(II), 72.6% for Co(II), and 68.5% for Cd(II). Among the investigated catalysts, Cu/NFO delivered the most favorable electrochemical performance, with a peak current density of 20.5 mA cm−2, an onset potential of 1.30 V vs. RHE in 1 M KOH containing 1 M methanol, and a fitted charge-transfer resistance of 4.24 Ω. Cu/NFO also retained 97.5% of its current after 12 h and 95.1% after 7000 cycles under the specified durability protocols. The superior response is attributed to the complementary contribution of surface Cu+/Cu2+ chemistry, defect-associated oxygen environments, improved electrochemical accessibility, and the open inter-particle architecture identified by the combined characterization results. The data support a synergistic surface-modification effect, although the contribution of each factor cannot be quantitatively separated by the present experiments. The retained magnetic response further provides a practical basis for investigating magnetic catalyst recovery. Overall, the results establish a materials-level waste-to-catalyst platform for alkaline methanol oxidation and motivate future validation in membrane-electrode assemblies and repeated recovery/reuse cycles.