Carbon quantum dots enriching molecular nickel polyoxometalate over CdS semiconductor for photocatalytic water splitting

An efficient and stable photocatalyst for overall water splitting is desirable for solar-energy conversion. Herein, Ni4P2-CQDs@CdS catalyst was obtained in situ photoreaction CQDs@CdS semiconductor composite and [Ni4(H2O)2(PW9O34)2]10- (Ni4P2) polyoxometallate. Photocatalytic hydrogen evolution from pure water is realized using CdS as the light harvester, CQDs as the electron acceptor and donor and Ni4P2 as catalyst without addition sacrificial reagents under visible light irradiation (lambda = 420 nm), which exhibits water splitting activity with H2 evolution rate up to 145 mu mol gcat -1 h-1. Experiments confirm the electrons transfer from CdS to CQDs, then to Ni4P2, resulting in accumulation of the electrons in Ni4P2 for H2 evolution. The generated holes at the VB of CdS transfer to CQDs and oxidize H2O to H2O2. The rotating ring-disk electrode test confirms the two-electron process (2H2O -> H2 + H2O2). This work proposes an elegant strategy for how to design multicomponent photocatalyst to realize efficient water splitting.