Photochemical construction of the ZnCdS/PO/FeCoNiPi–MnO composite for efficient tandem application of photocatalytic partial water splitting and overall water splitting

Abstract

Developing a sacrificial agent-free Zn_1−xCd_xS-based photocatalyst for efficient photocatalytic overall water splitting (POWS) is economical and eco-friendly but a challenging task. Herein, we synthesize a phosphorus (PO) protection layer and non-precious Fe_xCo_yNi_zP and MnO_a cocatalysts on Zn_0.4Cd_0.6S by a safe and energy-saving two-step photochemical strategy. The prepared Zn_0.4Cd_0.6S/PO/Fe_xCo_yNi_zPi–MnO_a photocatalyst displays average hydrogen and oxygen evolution rates of ∼1.14 mmol h⁻¹ g⁻¹ and ∼0.54 mmol h⁻¹ g⁻¹ in POWS, respectively, where Fe_xCo_yNi_zP and MnO_a act as the photogenerated electron and hole acceptors and provide the active sites for the two reactions. The superior POWS performance was maintained for 12 hours without any obvious attenuation. Moreover, photocatalytic partial water splitting (PPWS) is induced by the oxidation of NaH₂PO₂ during the photochemical synthesis process, yielding hydrogen evolution rates of 7.22 mmol h⁻¹ g⁻¹ and 5.90 mmol h⁻¹ g⁻¹, respectively. By integrating the two-step photochemical synthesis and POWS process (PPWS → PPWS → POWS), we obtain a total H₂ yield of about 4.85 mmol under 17 h visible light irradiation, which corresponds to an average H₂ evolution rate of 0.29 mmol h⁻¹. This work develops a safe and energy-saving photochemical synthesis strategy for Zn_1−xCd_xS-based photocatalysts, which not only exhibits excellent POWS performance but opens an avenue for the tandem application of PPWS and POWS to achieve a high H₂ total yield for solar-energy conversion.