Photocatalytic H2-production and benzyl-alcohol-oxidation mechanism over CdS using Co2+ as hole cocatalyst

The sluggish oxygen evolution reaction (OER) is often the bottleneck of photocatalytic overall water splitting, greatly suppressing the hydrogen-production activity. Herein, the slow OER was replaced by selective benzyl alcohol (BA) oxidation to benzaldehyde (BD) to promote H2 production. The photocatalytic reaction was conducted over CdS quantum dots, which were modified with Co2+ hole cocatalysts to further accelerate the rate-limiting BA oxidation. The photocatalytic system exhibits an ultra-high H2-production rate of 257.8 mmol g−1 h−1 with a remarkable apparent quantum yield of 69.3% under 365-nm light irradiation. The high performance is attributed to the Co2+ hole cocatalysts on CdS surfaces, which not only enhance light absorption but also facilitate photogenerated carrier transfer. More importantly, both photogenerated electrons and holes are fully utilized in meaningful reactions. This work exemplifies a bifunctional photocatalytic system for simultaneous production of self-separated hydrogen and benzaldehyde, both of which are important industrial products.