Photochemical H dissociation for nearly quantitative CO reduction to ethylene.

Producing olefins by carbon dioxide (CO) hydrogenation is a long-standing goal. The usual products are multicarbon mixtures because the critical step of heterolytic hydrogen (H) dissociation at high temperatures complicates selectivity control. In this study, we report that irradiating gold-titanium dioxide at 365 nanometers induces heterolytic H dissociation at ambient temperature.

Determining kinetics of HO evolution from photoelectrochemical water oxidation.

Photoelectrochemical water oxidation to generate HO is a clean and promising method. Its performance is strongly dependent on electrolyte species, in which the Faradaic efficiency is considerably promoted by HCO anion. The kinetic mechanism is under debate, which is highly desired but challenging.

Unraveling the Formation Kinetics of the First Intermediate in the Oxygen Evolution Reaction on MnO with Different Electron Configurations.

In the electrocatalytic oxygen evolution reaction (OER), it has been a long-standing issue to establish the relationship between intermediate kinetics, catalyst structures, and OER activity, which is challenging due to the difficulty in following the intermediate kinetics and charge dynamics simultaneously. Here, using home-built electrochemical transient absorption (EC-TA) spectroscopy, we succeeded in resolving the kinetics of the first intermediate (*OH species) in the OER catalytic cycle on MnO-based electrocatalysts, which is consistent with microkinetics simulation. In the formation process of *OH species, proton transfer is slower than electron transfer, resulting in the continuous formation of *OH species after the interruption of the potential pulse.

Parallel Regulation of Charge Dynamics on Bipolar Ferroelectric Surfaces Breaks the Limits for Water Splitting Efficiency.

Ferroelectric materials, known for their non-inversion symmetry, show promise as photocatalysts due to their unique asymmetric charge separation, which separates hydrogen and oxygen evolution sites. However, the strong depolarized field induces a relaxed surface structure, which in turn directly leads to slow hole charge transfer dynamics, hindering their efficiency in water splitting. In this study, a fundamental breakthrough in dramatically enhancing the overall water-splitting activity is presented, through the synergistically regulating of the surface behaviors of photogenerated carriers, resulting in nearly perfect parallel dynamics and balanced amounts.

Photoelectrochemical Imaging of Charge Separation between MoS Triangles and Insulating SiO Support.

The role of the insulating support in photocatalysis is poorly understood. Using high-resolution photo-scanning electrochemical microscopy (photo-SECM), we observed significant spatial charge separation in few-layer-thick molybdenum disulfide (MoS) triangles attached to a SiO substrate. Spatially resolved surface photovoltage (SPV) measurements revealed that photogenerated holes migrate from MoS to the SiO surface and travel laterally over distances exceeding 2 μm, driven by the built-in electric field of ∼1.

Intrafacet Charge Separation toward Efficient Overall Water Splitting on SrTiO Single Crystal Photocatalysts.

Facet engineering of photocatalytic particles has been proven to be effective in enhancing charge separation efficiency, particularly via interfacet built-in electric field, thus improving photocatalytic performance. However, whether charge separation also occurs within a facet remains unclear. Here, we found that reduction cocatalysts and oxidation cocatalysts are distributed on a facet of single cubic SrTiO crystal via photodeposition.

Impact of Reaction Environment on Photogenerated Charge Transfer Demonstrated by Sequential Imaging.

Most photocatalysis research focuses on understanding the photogenerated charge transfer processes within the solid catalysts themselves. However, these studies often overlook the impact of the reaction environment on photogenerated charge separation and reactions. To address this gap, our study employed a sequential imaging methodology that integrates surface photovoltage microscopy (SPVM), atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM) to track the transfer of photogenerated charges from the space charge region to the reactants at the nanoscale on individual BiVO particles.

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 .