Work-Function Engineering by Surface Modification of Hematite Photoelectrode via Layer-by-Layer Assembly for Water Splitting

Abstract

Artificial photosynthesis has drawn great attention for decades as a promising solution to energy and environmental problems. For example, we can produce valuable chemicals (e.g., formate, synthesis gas, and methanol) from abundant carbon dioxide and water through a series of photoelectrochemical processes in a carbon-neutral manner. For the successful development of efficient and stable photosynthetic devices, it is critical to precisely assemble various functional materials such as semiconductors for exciton generation, conducting materials for exciton dissociation and charge transport, and redox catalysts for target-chemical reactions. Here, we report the improvement of an efficient and stable, hematite-based photoelectrode for solar water splitting by layer-by-layer assembly (LbL) of cationic graphene oxide (GO) nanosheets and anionic molecular metal oxides as a charge transporting/separation material and water oxidation catalyst, respectively. It was found that their serial deposition significantly develops the photocatalytic performance and stability of the hematite photoelectrode by promoting charge transport and transfer across the electrode/electrolyte interface. Unexpectedly, it was also found that deposition of alternating layers of cationic and anionic functional materials allow us to engineer work-function of hematite photoelectrode beneficial for charge transport by forming an interfacial dipole layer at the surface of hematite. We believe that the present study can provide not only a general and simple method to fabricate an efficient photosynthetic device, but also an insight to scientists and engineers for designing of a novel electrochemical/photoelectrochemical device.