Photon-driven catalysis to generate solar fuels with inorganic molecules often requires the development of devices that incorporate mesoporous semiconductor films, where the films serve both as the scaffold on which to bind the molecules and as electron or hole acceptors that enable oxidative or reductive electrochemistry to be performed at the photoanode or photocathode, respectively. However, the identification of a high-performance semiconductor for the photocathode has remained a long-standing challenge. Here, we investigate the performance and passivation of the widely used photocathode material, NiO, and we also explore new approaches to the identification of alternate materials. The performance of NiO is strongly related to the presence of Ni vacancies, which introduce a distribution of trap states close to the valence band edge of the material and cause charge carrier recombination. We demonstrate a strategy to uniformly and selectively passivate defect sites using a vapor-phase process termed targeted atomic deposition (TAD). We observe that a volatile precursor such as trimethyl aluminum can undergo a kinetically-limited selective reaction with these sites. The TAD process effectively eliminates at least one type of dominant defect in NiO, and it leads to a dramatic reduction in recombination, enabling the operation of this material in aqueous solution. To move beyond NiO, we also demonstrate a materials informatics approach to identify new potential materials. By conducting a virtual screening of known compounds, we identify lead titanate (PbTiO<sub>3</sub>), a perovskite, as the most promising material. PbTiO<sub>3</sub> mesoporous films were fabricated and devices tested, exhibiting the best performance in aqueous solution. The results highlight the importance of both understanding defect states and rationally identifying new materials to identify photocathode systems that can be successfully used to generate solar fuels.

Design, synthesis, and passivation of metal oxide photocathodes for aqueous solution: Fixing and moving beyond NiO

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.