Surface photovoltage microscopy for mapping charge separation on photocatalyst particles.

Solar-driven photocatalytic reactions offer a promising route to clean and sustainable energy, and the spatial separation of photogenerated charges on the photocatalyst surface is the key to determining photocatalytic efficiency. However, probing the charge-separation properties of photocatalysts is a formidable challenge because of the spatially heterogeneous microstructures, complicated charge-separation mechanisms and lack of sensitivity for detecting the low density of separated photogenerated charges. Recently, we developed surface photovoltage microscopy (SPVM) with high spatial and energy resolution that enables the direct mapping of surface-charge distributions and quantitative assessment of the charge-separation properties of photocatalysts at the nanoscale, potentially providing unprecedented insights into photocatalytic charge-separation processes.

Visualizing the role of applied voltage in non-metal electrocatalysts.

Understanding how applied voltage drives the electrocatalytic reaction at the nanoscale is a fundamental scientific problem, particularly in non-metallic electrocatalysts, due to their low intrinsic carrier concentration. Herein, using monolayer molybdenum disulfide (MoS) as a model system of non-metallic catalyst, the potential drops across the basal plane of MoS (ΔV) and the electric double layer (ΔV) are decoupled quantitatively as a function of applied voltage through surface potential microscopy. We visualize the evolution of the band structure under liquid conditions and clarify the process of E keeping moving deep into E, revealing the formation process of the electrolyte gating effect.

Graphene Mediates Charge Transfer between Lead Chromate and a Cobalt Cubane Cocatalyst for Photocatalytic Water Oxidation.

The interfacial barrier of charge transfer from semiconductors to cocatalysts means that the photogenerated charges cannot be fully utilized, especially for the challenging water oxidation reaction. Using cobalt cubane molecules (Co O ) as water oxidation cocatalysts, we rationally assembled partially oxidized graphene (pGO), acting as a charge-transfer mediator, on the hole-accumulating {-101} facets of lead chromate (PbCrO ) crystal. The assembled pGO enables preferable immobilization of Co O molecules on the {-101} facets of the PbCrO crystal, which is favorable for the photogenerated holes transferring from PbCrO to Co O molecules.

Spatiotemporal imaging of charge transfer in photocatalyst particles.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production. Photo-induced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometres to micrometres and from femtoseconds to seconds. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown.

Tuning the Anisotropic Facet of Lead Chromate Photocatalysts to Promote Spatial Charge Separation.

A crucial issue in artificial photosynthesis is how to modulate the behaviors of photogenerated charges of semiconductor photocatalysts. Here, using lead chromate (PbCrO ) as an example, we conducted the morphology tailoring from parallelepiped (p-PbCrO ) to truncated decahedron (t-PbCrO ) and elongated rhombic (r-PbCrO ), resulting in exposed anisotropic facets. The spatial separation of photogenerated charges closely correlates to the anisotropic facets of crystals, which can only be realized for t-PbCrO and r-PbCrO .