Enhanced photoelectrochemical performance of P-doped g‑C₃N₄/Zn_0.5Cd_0.5S heterojunction photocathode for water splitting

Photoelectrochemical (PEC) hydrogen evolution reaction at semiconductor photocathode in the presence of visible light is a promising way to harvest renewable energy. Graphitic carbon nitride (g-C₃N₄) has intriguing properties, making it highly favorable for photoelectrode engineering. This work demonstrated P-doped g-C₃N₄ nanosheets (PCN-Nss) and Zn_0.5Cd_0.5S heterojunction (PCN-Nss/ZCS-40) for PEC hydrogen evolution reaction using simulated sunlight. A facile and simple two-step strategy developed PCN-Nss/ZCS-40 photocathode; including co-precipitation of ZnCdS in the highly dispersed suspension of PCN-Nss and then drop-casting it on the surface of a conductive substrate. The intimate contact between PCN-Nss and ZnCdS at the molecular level due to the formation of heterojunction efficiently triggers charge separation, suppressing electron-hole pair recombination and easing the movement of photo-generated holes towards the conductive substrate. PCN-Nss/ZCS-40 (40% P-C₃N₄ by weight) showed substantially improved photocurrent response (−12 µA cm⁻²) at −0.6 V vs Ag/AgCl reference electrode in 0.2 M Na₂S solution, which is almost 40 times greater than simple P-C₃N₄ nanosheets under the same conditions. This work will expose new applications for P-doped graphitic carbon nitride-based heterostructures for PEC water splitting.