Application of Composite Film Containing Polyoxometalate Ni25 and Reduced Graphene Oxide for Photoelectrocatalytic Water Oxidation

The preparation of clean energy is an effective way to solve the global energy crisis and reduce environmental pollution. The decomposition of water can produce hydrogen and oxygen, which is one of the effective ways to prepare clean energy. However, water oxidation is a bottleneck for water decomposition, thus, developing a water oxidation catalyst can accelerate the process of water decomposition to generate clean energy. Nickel-substituted polyoxometalate [Ni25(H2O)2(OH)18(CO3)2(PO4)6(SiW9O34)6]50− (Ni25) is proven as an excellent water oxidation photocatalyst. To develop the effective photoelectrocatalyst for water oxidation, in this work, we constructed two composite films containing Ni25 on ITO, [PDDA/Ni25]n, and PDDA/[Ni25/(PDDA–rGO)]n, by layer-by-layer self-assembly, which is the first combination of nickel-substituted polyoxometalates and reduced graphene oxide (rGO). The study on the photoelectrocatalytic performance of the two films indicates that the water oxidation current of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode is increased by 33.7% after light irradiation, which is 1.71 times that of the film [PDDA/Ni25]n-modified electrode. Moreover, the transient photocurrent response of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode demonstrates that there is a synergistic effect between rGO and Ni25, and rGO-accelerated electron transport and inhibited charge recombination. In addition, the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode exhibits good stability, indicating its great potential as an effective photoelectrocatalyst for water oxidation in practical application.