Cobalt incorporation-induced photocatalytic reactivity enhancement in ZnIn₂S₄ nanosheets for effective hydrogen production

Heteroatom incorporation is commonly used resorts to construct highly active centers in photocatalysis. Especially, cobalt with tunable spin orbitals is a desirable dopant for photocatalytic hydrogen production. However, the charge and adsorption properties associated with cobalt-incorporated sites have not been elucidated. In this work, the cobalt with the spin state (e⁴t₂³) was successfully incorporated into ZnIn₂S₄ nanosheets. Experimental and calculated results show that the cobalt-induced electron occupancy displays an obvious interaction with oxygen-containing intermediates, which promotes water dissociation. Meanwhile, the enhanced covalency of Co[sbnd]S bonds effectively balances the hydrogen adsorption/desorption ability, which is favorable for H₂ production. Nevertheless, the weakened water adsorption restricts the improvement of H₂ production as the amount of Co doping increases. Under the balance of these factors, optimum doping of cobalt in ZnIn₂S₄ is achieved and it shows a significantly enhanced H₂-evolution rate of 72.1 μmol h⁻¹, which is 5.5 times higher than that of ZnIn₂S₄.