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ABSTRACT Metal/carbon‐based nanocomposites have attracted significant interest for electrochemical water splitting due to their unique interfacial electronic structures, abundant active sites, and catalytic bifunctionality toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Co/CoO‐rGO composites consisting of Co/CoO heterostructured nanoparticles encapsulated within a graphitized carbon scaffold are produced via magnetic induction heating at controlled currents for 10 s with cobalt(II) nitrate and reduced graphene oxide (rGO) loaded on nickel foam and effectively catalyze both HER and OER in alkaline media. Among the series, the sample prepared at 400 A for 10 s exhibits the best performance, featuring an overpotential of −144 mV for HER and +390 mV for OER at 10 mA cm⁻²and 50 mA cm⁻², respectively. The bifunctional activity can then be exploited for full water splitting, where a low cell voltage of 1.61 V is needed to generate a current density of 10 mA cm⁻², 260 mV better than that with commercial Pt/C and RuO₂. The remarkable performance is attributed to the synergistic interaction between the Co and CoO domains, enhanced charge transfer at the heterojunction interface, and conductive carbon support. These results highlight the potential of Co/CoO‐based nanocomposites as efficient and low‐cost catalysts for overall water splitting and the scalability of the MIH technology. 

Ruthenium has emerged as a promising substitute for platinum toward the hydrogen evolution/oxidation reaction (HER/HOR). Herein, ruthenium/carbon composites are prepared by magnetic induction heating (300 A, 10 s) of RuCl₃, RuBr₃or RuI₃loaded on hollow N‐doped carbon cages (HNC). The HNC‐RuCl₃‐300A sample consists of Ru nanoparticles (dia. 1.96 nm) and abundant Cl residues. HNC‐RuBr₃‐300A possesses a larger nanoparticle size (≈19.36 nm) and lower content of Br residues. HNC‐RuI₃‐300A contains only bulk‐like Ru agglomerates with a minimal amount of I residues, due to reduced Ru‐halide bonding interactions. Among these, HNC‐RuCl₃‐300A exhibits the best HER activity in alkaline media, with a low overpotential of only −26 mV to reach 10 mA cm⁻², even outperforming Pt/C, and can be used as the cathode catalyst for anion exchange membrane water electrolyzer (along with commercial RuO₂as the anode catalyst), producing 0.5 A cm⁻²at 1.88 V for up to 100 h, a performance markedly better than that with Pt/C. HNC‐RuCl₃‐300A also exhibits the best HOR activity, with a half‐wave potential (+18 mV) even lower than that of Pt/C (+35 mV). These activities are ascribed to the combined contributions of small Ru nanoparticles and Ru‐to‐halide charge transfer that weaken H adsorption.