Fe Cluster Modified Co9S8 Heterojunction: Highly Efficient Photoelectrocatalyst for Overall Water Splitting and Flexible Zinc‐Air Batteries

Abstract Designing bifunctional low‐cost photo‐assisted electrocatalysts for converting solar and electric energy into hydrogen energy remains a huge challenge. Herein, a heterojunction (Fe cluster modified Co 9 S 8 loaded on carbon nanotubes, Co 9 S 8 ‐Fe@CNT) for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is demonstrated. Benefiting from the good electronic conductivity and spatial confinement of the carbon skeleton, as well as the electronic structure regulation of the Fe cluster, Co 9 S 8 ‐Fe@CNT exhibits excellent catalytic performance with a low overpotential of 150 mV for OER and 135 mV for HER at 10 mA cm −2 . Upon light irradiation, holes and electrons are generated in the valence band and conduction band of the Co 9 S 8 , respectively. Part of the charges are transferred to the interface to facilitate the catalytic reaction, while the remaining are transferred by the electrode. When working as a bifunctional catalyst for overall water splitting, the performance can reach 1.33 V at under light conditions, which is significantly better than 1.52 V in a dark environment. Theoretical calculations revealed lowered Gibbs free energy (∆ G H *) of the heterojunction with the effect of Fe modification of Co 9 S 8 . This work sheds a new light in designing novel photoelectrochemical materials to convert solar and electric energy into chemical energy.