Sub‑1 nm high-entropy oxide nanosheets for robust oxygen evolution reaction at large current density

The lack of efficient and low-cost catalysts hinders the large-scale application of electrolytic water splitting. High-entropy oxides (HEOs) offer unique structures and promising properties for oxygen evolution reaction (OER) but are often synthesized via high-temperature methods, resulting in microscale particles with low active site exposure. HEO sub-1 nm nanosheets (SNSs) are synthesized using a cluster-nuclei co-assembly strategy with the introduction of phosphomolybdic acid (PMA) clusters. Molecular dynamics simulation results demonstrate that the PMA clusters act as linkers, facilitating the co-assembly of multimetal oxides into stable and ordered nanosheets via noncovalent interactions. Owing to the sub-nanoscale structure and precise elemental regulation, these SNSs demonstrate enhanced performance in OER. Among them, HEO-PMA SNSs demonstrated superior performance, achieving an overpotential of 229 mV at 10 mA cm−2 and exceptional long-term stability that lasted for over 1000 h at a large current density of 250 mA cm−2. Density functional theory calculations also demonstrate that the synergistic effect of multiple metals can significantly enhance the OER process. Composition engineering and sub-1 nm structural design in HEOs provide a promising strategy to enhance catalyst stability, addressing challenges related to low intrinsic activity, scarce active sites, and long-term durability in the OER process.