In-situ transient photovoltage study on interface electron transfer regulation of carbon dots/NiCo₂O₄ photocatalyst for the enhanced overall water splitting activity

Photocatalytic hydrogen production by overall water solar-splitting is a prospective strategy to solve energy crisis. However, the rapid recombination of photogenerated electron–hole pairs deeply restricts photocatalytic activity of catalysts. Here, the in-situ transient photovoltage (TPV) technique was developed to investigate the interfacial photogenerated carrier extraction, photogenerated carrier recombination and the interfacial electron delivery kinetics of the photocatalyst. The carbon dots/NiCo₂O₄ (CDs/NiCo₂O₄) composite shows weakened recombination rate of photogenerated carriers due to charge storage of CDs, which enhances the photocatalytic water decomposition activity without any scavenger. CDs can accelerate the interface electron extraction about 0.09 ms, while the maximum electron storage time by CDs is up to 0.7 ms. The optimal CDs/NiCo₂O₄ composite (5 wt.% CDs) displays the hydrogen production of 62 µmol·h⁻¹·g⁻¹ and oxygen production of 29 µmol·h⁻¹·g⁻¹ at normal atmosphere, which is about 4 times greater than that of pristine NiCo₂O₄. This work provides sufficient evidence on the charge storage of CDs and the interfacial charge kinetics of photocatalysts on the basis of in-situ TPV tests.