ABSTRACT

Solar water splitting provides a sustainable and environmentally benign route for the production of hydrogen gas for use as a clean fuel source. This is why low cost and efficient solar water splitting is one of the grand scientific challenges. One way to split water with sunlight is with a photoelectrochemical cell (PEC), but these devices are not yet efficient enough for practical use. This project examines methods of optimizing parts of the PEC: the catalyst and protection layers that are key components for efficient and sustainable solar water splitting. It also examines the semiconductor electrodes that harvest solar energy, then generate and transport the electrical charge used for hydrogen generation. The overall performance of a PEC is affected not only by the bulk properties of these individual parts, but also by the interfaces formed between them. However, the difficulty of studying the interfaces relevant to water splitting have stood in the way of their study. In this project, Dr. Kyoung-Shin Choi of the University of Wisconsin - Madison and Dr. Giulia Galli of the University of Chicago combine experimental and computational studies to understand and control interfacial properties of a representative PEC system - bismuth vanadate-based photoanodes and their interfaces with other metal oxides. This project makes it possible to devise general strategies to construct optimal interfaces between the different parts of a PEC to enhance solar water splitting. Dr. Choi and Dr. Galli are also setting up combined experimental-computational tutorials to teach researchers in the field how to best compare computational and experimental results. Finally, they are creating and maintaining a website that contains useful data on PECs that can be accessed and used by researchers worldwide.

In a photoelectrochemical cell (PEC), in addition to semiconductor electrodes that harvest solar energy and generate/transport charge carriers, catalyst and protection layers are key components for efficient and sustainable solar water splitting. The overall performance of multicomponent photoelectrodes is affected not only by the bulk properties of the individual constituents but also by the interfaces formed between them. The characteristics of these interfaces can considerably affect the charge transport properties and recombination loss, thus determining the number of charge carriers reaching the electrode surface to participate in water splitting reactions. To date, systematic studies of the atomic and electronic structures of interfaces relevant to water splitting have been extremely rare, due to numerous experimental and computational challenges. In this project, Dr. Choi and Dr. Galli are establishing a general and fundamental understanding of the effect of interfacial atomic and electronic structures on photoelectrochemical properties by combining experimental and computational studies. In order to elucidate interface-photoelectrochemical property relationships, BiVO4-based photoanodes are used as a representative multicomponent photoelectrode system, and a series of semiconductor/oxygen evolution catalyst (OEC), semiconductor/protection layer, and protection layer/OEC interfaces are constructed and examined by using single crystal and polycrystal BiVO4 electrodes with systematically varied surface terminations. An atomic level understanding of interface-photoelectrochemical property relationships makes it possible to devise general strategies to construct optimal interfaces among photon absorbers, protective materials, and catalysts to enhance solar water splitting. The proposed work also provides the community with validated coupled experimental-computational strategies for studying complex, heterogeneous interfaces.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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