Ultrafine IrO _<i>x</i> Nanocluster-Modified Carbon Nanotubes Encapsulating Fe Nanoparticles: A Highly Efficient Self-Supported Electrode for Overall Water Splitting

Self-supported electrodes featuring transition metals encapsulated within carbon nanotubes (CNTs) are promising bifunctional catalytic electrodes for overall water splitting due to their binder-free fabrication (eliminating costly Nafion), high electrical conductivity, mechanical strength, and low cost. However, challenges remain, including insufficient catalytic activity and stability, as well as underutilization of the CNTs’ functionality. Herein, we strategically modified a Fe-based self-supported electrode with ultrafine IrOx nanoclusters (IrOx NCs), creating Fe@CNTs/IrOx NCs/CC, which exhibits enhanced bifunctional performance for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH. The optimized Fe10@CNTs/IrOx NCs/CC requires low HER and OER overpotentials of 36.7 mV and 203.5 mV at the current density of ± 10 mA cm–2. It also shows a high mass activity of 214.8 A gIr–1 at 100 mV. Moreover, water splitting cells employing Fe10@CNTs/IrOx NCs/CC as both the anode and cathode require only 1.50 V to reach 10 mA cm–2 and demonstrate stable operation exceeding 100 h. Detailed theoretical calculations prove that the IrOx NCs synergistically enhance HER kinetics by promoting both the H2O adsorption-dissociation efficiency and optimized *H desorption. For the OER process, they significantly lower the energy barrier of the rate-determining step (*O → *OOH), thereby accelerating the overall water splitting process of Fe10@CNTs/IrOx NCs/CC. This work highlights an innovative research route for boosting the water splitting performance through targeted modification of the self-supported electrode.