Spatiotemporal imaging of anisotropic charge transfer in photocatalyst particles

Water-splitting reactions using photocatalyst particles are promising routes for solar fuel production1-4. Photoinduced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency5; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometers to micrometers and from femtoseconds to seconds6-8. Although the steady-state charge distribution on single photocatalyst particles has been mapped using microscopic techniques9-11 and the averaged charge transfer dynamics in photocatalyst aggregations have been revealed via time-resolved spectroscopy12,13, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and the mechanism of charge transfer is unknown. Here, we report spatiotemporally resolved surface photovoltage measurements on Cu2O photocatalyst particles to map complete charge transfer processes throughout the femtosecond to second time scale at the single-particle level. We found that photogenerated electrons are transferred to the catalytic surface ballistically on a sub-picosecond timescale and are retained at this location for the duration, whereas photogenerated holes are transferred to a spatially separated surface and stabilized via selective trapping on a microsecond timescale. We demonstrate that these ballistic electron transfer and anisotropic trapping regimes, which challenge the classical perception of the drift–diffusion model, contribute to efficient charge separation in photocatalysis and improve the photocatalytic performance. We anticipate our findings to demonstrate the universality of other photoelectronic devices and facilitate the rational design of photocatalysts.