Harnessing the Catalytic Competency of Nonprecious Co–Fe Oxalate Microstructure and Nonstoichiometric Co0.85Se Toward Alkaline Overall Water Splitting

Designing efficient cobalt-based electrocatalysts for the alkaline oxygen evolution reaction (OER) is a tedious task owing to limited per-site activity. However, the interfacial modulation by the insertion of low-cost iron considerably stimulates both geometric and intrinsic activity of cobalt centers. Here, we have prepared a series of bimetallic cobalt-iron oxalate composites (CoxFe1-xC2O4, where x = 1 to 0) via a simple coprecipitation method. The thorough physical studies confirm the development of efficient interfacial junctions between Co and Fe oxalate microstructures. Among the as-prepared CoxFe1-xC2O4 (where x = 1 to 0) composites, the Co0.6Fe0.4C2O4 exhibits the best catalytic proficiency, requiring only 292 ± 4 and 361 ± 5 mV overpotentials to achieve the benchmark 10 and 100 mA cm-2geo current density on a carbon paper substrate. The corresponding overpotentials are further reduced to 245 ± 5 and 288 ± 5 mV on nickel foam (NF) substrate. The swift reaction kinetics (Tafel slope ≈ 32 mV dec-1), low charge-transfer resistance, and enduring 48 h stability make the Co0.6Fe0.4C2O4 well-suited for alkaline OER. In addition, the Fe incorporation into Co centers induces strong synergistic interactions, improves surface porosity, and enhances the turnover frequency (TOF ≈ 0.95 s-1). Further, the Co-Fe bimetallic system showcases the notably low activation energy, indicating the excellent catalytic competency of the Co0.6Fe0.4C2O4 composite at a high operating voltage and current density. The isotope labeling study uncovered the occurrence of the adsorbate evolution mechanism (AEM) within the Co0.6Fe0.4C2O4 composite during alkaline OER catalysis. Meanwhile, to demonstrate the overall water splitting, the cobalt oxalate-assisted Co3O4 was hydrothermally transformed into Co0.85Se, showcasing 141 mV @ -10 mA cm-2 towards alkaline hydrogen evolution reaction (HER). Finally, the Co0.6Fe0.4C2O4 (+) || Co0.85Se (-) electrolyzer was constructed, delivering 1.68 V cell voltage to accomplish 10 mA cm-2 current density on carbon paper substrate and 36 h prolonged stability with a negligible performance drop.