Rational Design Of Photocatalysts Research Articles

New insight into efficient photocatalytic CO2 reduction without any sacrifice agent over the novel hierarchical structured SiOC whisker aerogel

Photoreduction of CO2 to valuable fuels provides a promising strategy for managing the global carbon balance using renewable solar energy, yet the design of active, cost-effective, highly selective, and stable CO2 reduction photocatalysts remains a big challenge. Herein, we report a novel SiOC aerogel photocatalyst synthesized by a simple one-step sol-gel process, combined with the supercritical drying technique and heat treatment processes. The resulting SiOC aerogel exhibits a large BET specific area with typical hierarchical structures, which is responsible for the enhanced photocatalytic activity. In addition, the formation mechanism of the SiOC whisker aerogel is revealed in this study. The optimized SiOC aerogel exhibits CH4 and CO evolution activity of 5.8 and 20.5 μmol/g under simulated sunlight irradiation, respectively, without any additional co-catalyst or sacrificial agent, which is 6.4 and 3.9 times higher than those of the pristine SiC aerogel. The density functional theory (DFT) calculation confirms that the resulting SiOC aerogel can effectively adsorb and activate CO2 and H2O molecules on the catalyst surface. The Gibbs free energy diagram further verifies the superior performance of the resulting SiOC aerogel over the pristine SiC and SiO2 cluster via the rate-determining step calculations. The high efficiency of CO2 reduction can be attributed to the structural merits and the electronic structures modulation, which greatly achieves fast separation and transfer of charge carriers. The work paves an insight into the rational design of photocatalysts toward simultaneously facilitating carrier separation and CO2 activation from aerogel-based porous materials.

Revealing the Importance of Hole Transfer: Boosting Photocatalytic Hydrogen Evolution by Delicate Modulation of Photogenerated Holes

Photocatalytic hydrogen evolution (PHE) has gained massive attention for the development of renewable resources. Currently, prominent and stable PHE is still restricted by the limited utilization of photocatalytic charge carriers, especially holes, of which the transfer rate is approximately two to three orders of magnitude slower than that of electrons. Although it is widely accepted that surface holes can be consumed by electron donors, the rational design of photocatalysts to speed up hole transfer and understand the ultrafast photodynamics as well as the exploration of the effect of oxidation products is still highly urgent. Herein, cadmium sulfide (CdS), as the model photocatalyst, is investigated for prominent PHE based on hole modulation strategies. To accelerate the surface reaction, H2S-saturated Na2S&Na2SO3 solution, which outperforms traditional hole scavengers, is selected to remove the holes accumulating on the photocatalyst surface, while the oxidative cocatalyst palladium sulfide (PdS) is simultaneously impregnated on CdS to optimize the hole transfer process. Evidenced by femtosecond transient absorption spectroscopy (TAS) and band structure analysis, the ultrafast process (1–5 ps) highly related with hole transfer from CdS to PdS is proved in the CdS/PdS composite. More importantly, density functional theory (DFT) calculation suggests that the hole accumulation site (PdS) is also the oxidation active site where the active species (HS*) adsorbs on. Finally, the oxidation product composition is analyzed through Fourier transform infrared (FTIR) spectroscopy, which indicates that the colorless and value-added product S2O32– protects the photocatalyst from the light shielding effect. Contributed by factors mentioned above, improved PHE efficiency (∼145.9 mmol·g–1·h–1) is achieved on the CdS/PdS composite.

Effects of surface fluoride modification on TiO2 for the photocatalytic oxidation of toluene

In the present study, we investigated the influence of surface fluorine (F) on TiO2 for the photocatalytic oxidation (PCO) of toluene. TiO2 modified with different F content was prepared and tested. It was found that with the increasing of F content, the toluene conversion rate first increased and then decreased. However, CO2 mineralization efficiency showed the opposite trend. Based on the characterizations, we revealed that F substitutes the surface hydroxyl of TiO2 to form the structure of Ti-F. The presence of the appropriate amount of surface Ti-F on TiO2 greatly enhanced the separation of photogenerated carriers, which facilitated the generation of ·OH and promoted the activity for the PCO of toluene. It was further revealed that the increase of only ·OH promoted the conversion of toluene to ring-containing intermediates, causing the accumulation of intermediates and then conversely inhibited the ·OH generation, which led to the decrease of the CO2 mineralization efficiency. The above results could provide guidance for the rational design of photocatalysts for toluene oxidation.

Biomass Photoreforming for Hydrogen and Value‐Added Chemicals Co‐Production on Hierarchically Porous Photocatalysts

AbstractBiomass, a naturally abundant, sustainable and clean resource has great potential as an alternative to replace the limited fossil feedstock for value‐added chemicals and fuels. Biomass with abundant reductive functional groups could theoretically act as electron donor to consume photogenerated holes and/or active free radicals. Biomass photoreforming over semiconductor photocatalysts using solar light as energy input attracts much attention in this context. However, biomass photoreforming still suffers low conversion efficiency and product selectivity due to its structural complexity, poor solubility and unclear reaction mechanism. Owing to the advanced features of mass diffusion of biomass derivatives and adjustable surface properties, hierarchically porous photocatalysts with desired active sites at each length scale of porosity have shown their superiority in boosting the conversion efficiency and selectivity of biomass photoreforming. Herein, a critical review is presented on selective biomass photoreforming for simultaneous H2 and value‐added chemicals co‐production on hierarchically porous photocatalysts. The fundamentals of biomass photoreforming and current bottleneck of biomass valorization by photocatalytic process are presented and analyzed. The rational photocatalyst design with hierarchically porous structure to improve the biomass conversion and product selectivity by boosting mass transfer is highlighted. Finally the challenges and opportunities for photocatalytic biomass valorization are presented in the perspective ssection.

Operando Laboratory X-ray Absorption Spectroscopy and UV–Vis Study of Pt/TiO2 Photocatalysts during Photodeposition and Hydrogen Evolution Reactions

Photocatalytic hydrogen (H2) production is a promising route for alternative energetics. Understanding structure–activity relationships is a crucial step towards the rational design of photocatalysts, which requires the application of operando spectroscopy under relevant working conditions. We performed an operando investigation on a catalytic system during the photodeposition of Pt on TiO2 and photostimulated H2 production, using simultaneous laboratory X-ray absorption spectroscopy (XAS), UV–Vis spectroscopy, and mass spectrometry. XAS showed a progressive increase in Pt fluorescence for Pt deposited on TiO2 for over an hour, which is correlated with the signal of the produced H2. The final Pt/TiO2 catalyst contained Pt(0) particles. The electronic features corresponding to the Pt4+ species in the UV–Vis spectrum of the solution disappear as soon as UV radiation is applied in the presence of formic acid, which acts as a hole scavenger, resulting in the presence of Pt(0) particles in solution.

Self-assembly synthesis of hollow phosphorus-doped graphitic carbon nitride microboxes for the photodegradation of organic pollutants.

The rational design of photocatalysts with efficiency and stability is highly desirable but remains challenging. Here, we report a supramolecular self-assembly strategy to construct hollow phosphorus-doped g-C3N4 microboxes (PCNMs). Considering the effects of multiple parameters on the structure and activity of samples, the orthogonal design is innovatively introduced to optimize technology parameters for screening high-performance g-C3N4. Under visible light irradiation (λ ≥ 420 nm), rhodamine B (RhB, 4 mg L-1) is completely degraded in just 80 seconds in the presence of the optimal PCNM. The kinetic rate constant of RhB degradation with the PCNM is 3.4633 min-1, demonstrating unprecedented activity that is about 112 times higher than that of bulk g-C3N4 (0.0309 min-1) synthesized by direct polycondensation of melamine. Additionally, the optimal PCNM also shows enhanced degradation efficiency for tetracycline. The outstanding properties are primarily attributed to the hollow architecture, high specific surface area, and phosphorus doping. This work advances the design of photocatalysts correlating various factors, opening an avenue for optimizing photocatalytic synthesis and activity.

Quantitative prediction of excited-state decay rates for radical anion photocatalysts.

We present a computational approach for predicting key properties of organic radical anions, including excited-state lifetimes and redox potentials. The approach shows good agreement with experimental data and has potential for in silico screening to facilitate the rational design of photocatalysts.

Metallic Bi and oxygen vacancy dual active sites enable efficient oxygen activation: Facet-dependent effect and interfacial synergy

Surface atomic arrangement and coordination of different crystal facets significantly affect the catalytic reactivity of photocatalysts. By modulating the solvent environment, we developed a one-step solvothermal route to synthesize a series of BiOBr nanosheets with different dominating facets ((001) and (010)) and simultaneously decorated metallic Bi and oxygen vacancies (OVs) on the identified preferred facets ((010)). The resulting Bi/OV-BiOBr-(010) outperform BiOBr-(010) with mono OVs, bare BiOBr-(010), and other well-known photocatalysts in both O2 activation and pollutant degradation under both same catalyst loading and optical thickness conditions. The synergistic effects of the Bi-OV dual active sites in O2 adsorption-activation and charge separation-transfer were confirmed by experimental characterization and DFT calculation. This study highlights the facet-dependent synergy of plasmonic metal-defect dual active sites and shed light on the rational design of photocatalysts for more efficient O2 activation and refractory pollutant degradation.

Heterojunction within dual electric fields dynamically tailoring charge transfer to surface redox active sites for efficient H2 generation

Flying broom-like heterojunction photocatalysts with internal electric field synergizing polarized field has been constructed by spontaneously assembling CuO nanoparticles on polarized g-C3N4 microfibers (p-C3N4Fs) with using a facile hydrothermal method. Theoretical prediction and characterizations confirm that, photo-generated electrons and holes are dynamically transferred to reductive sites of pyridine-like N in p-C3N4Fs and oxidative sites of Cu atom in CuO for H2O splitting within the dual electric fields, respectively. Stoichiometric H2 and O2 evolution with solar energy conversion into H2 energy of 1.22 % has been achieved under AM 1.5G irradiation in photocatalytic H2O overall splitting by heterojunction photocatalytic mechanism of translation, rotation, transformation of protons and intermediates. The rational photocatalyst design on heterojunction with dual electric fields breaks the long-term thought of regulating charge carriers only by internal electric field, which will provide a unique perspective to deepen the kinetic study on the spatial separation and directional migration of photogenerated charges to the surface redox active sites for solar energy conversion.

Enwrapping g-C3N4 on In2O3 hollow hexagonal tubular for photocatalytic CO2 conversion: Construction, characterization, and Z-scheme mechanism insight

The reduction of CO2 achieved by photocatalysis can simultaneously alleviate the energy crisis and solve environmental issues. Nevertheless, it remains challenging for the rational design of photocatalysts with high-efficiency carrier migration ability. Herein, the Z-scheme g-C3N4/In2O3 (CN/INO) heterostructure was fabricated via metal–organic frameworks (MOFs) assisted thermal deposition which could form a fully encapsulated hollow tubular structure. The unique structure was based on the MOFs-derived hollow hexagonal In2O3 tubular integrated with ultrathin g-C3N4. The Z-scheme CN/INO heterojunction exhibited a larger specific surface area and excellent charge separation efficiency. Benefiting from the above features, the Z-scheme CN/INO heterojunction demonstrated superior performance on photocatalytic CO2 reduction. The formation of CO and CH3OH over the optimized CN/INO-2 catalyst was 7.94 and 1.44 µmol⋅g−1⋅h−1, respectively. Moreover, the density functional theory (DFT) calculations and Kelvin probe force microscopy (KPFM) was carried out to further investigate the situation of charge transfer on the interface of CN/INO. The in-situ Fourier transform infrared spectroscopy (FTIR) was measured to confirm the immediate products and the possible mechanism of photocatalytic CO2 reduction was proposed. This work provided a MOFs-assisted strategy to construct a Z-scheme system for photocatalytic CO2 reduction.

Cellular-level insight into biointerface: From surface charge modulation to boosted photocatalytic oxidative disinfection

Photocatalytic oxidative disinfection (POD) towards pathogenic bacteria has become a popular approach in public health due to its environmentally friendly antimicrobial capabilities. However, this approach is still limited by inherent fast electron-hole recombination within photocatalysts and poor interactions between bacterial cells and photogenerated reactive oxygen species (ROS) at the biointerface. Particularly, those ROS with extremely short migration distances cannot reach the bacterial cells before they deteriorate into less potent or neutral species, resulting in reduced antibacterial activities. By far, these phenomena are still poorly understood. Inspired by the fact that bacterial cells are negatively charged, we rationally designed a photocatalyst (i.e., g-C3N4/MIL-125-NH2) by coating a layer of positively charged quaternary ammonium compound (QAC) polymer onto the surface to enhance its affinity towards bacterial cells via electrostatic attractions. This surface-modulated photocatalyst is denoted as QAC@g-C3N4/MIL-125-NH2. The visualization and quantification of the electrostatic interactions between the bacterial cells and the QAC@g-C3N4/MIL-125-NH2 photocatalyst were conducted using a confocal laser scanning microscope and atomic force microscope, respectively. The results showed that the positively charged QAC layer did promote the bacteria-photocatalyst contact via electrostatic attractions. Due to the cooperative effects of bacterial cell adhesion and ROS generation, the POD performance of the photocatalyst is significantly enhanced. Notably, the photocatalyst achieves 3.20 logs of inactivation efficiency for Staphylococcus epidermidis within 60 min under visible light irradiation. This work provides insights into a mechanistic understanding of bacterial adhesion and disinfection at the biointerface and sheds light on rational photocatalyst design with surface charge modulation for antibacterial applications.

Spatiotemporal imaging of charge transfer in photocatalyst particles.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production1-4. Photo-induced 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 nanometres to micrometres and from femtoseconds to seconds6-8. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques9-11, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy12,13, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown. Here we perform spatiotemporally resolved surface photovoltage measurements on cuprous oxide photocatalyst particles to map holistic charge transfer processes on the femtosecond to second timescale at the single-particle level. We find that photogenerated electrons are transferred to the catalytic surface quasi-ballistically through inter-facet hot electron transfer on a subpicosecond timescale, whereas photogenerated holes are transferred to a spatially separated surface and stabilized through selective trapping on a microsecond timescale. We demonstrate that these ultrafast-hot-electron-transfer and anisotropic-trapping regimes, which challenge the classical perception of a drift-diffusion model, contribute to the efficient charge separation in photocatalysis and improve photocatalytic performance. We anticipate that our findings will be used to illustrate the universality of other photoelectronic devices and facilitate the rational design of photocatalysts.

Hierarchical Bi2WO6/BiFeWO6 n-n heterojunction as an efficient photocatalyst for water splitting under visible light

A hierarchical Bi 2 WO 6 /BiFeWO 6 architectures were synthesized by a facile and low-cost hydrothermal approach using Bi 2 WO 6 flower structure as an efficient backbone for the growth of layered BiFeWO 6 sheets. The conduction band offset and bandgap of flower like Bi 2 WO 6 were tailored strategically as active photocatalyst under visible light and suitable for water reduction. By developing n-n heterojunction between Bi 2 WO 6 and BiFeWO 6 , the active surface area as well as number of free charge carriers have been enhanced which may boost the catalytic redox reactions. The physicochemical properties of the heterojunction was characterized to investigate the phase, morphology, thermal stability, light absorption and oxidation states of the elements. The photocatalytic activity of Bi 2 WO 6 /BiFeWO 6 heterojunction was investigated through H 2 generation via water splitting under visible light, where four-fold enhanced activity achieved for heterojunction compared to bare Bi 2 WO 6 . Further, photoelectrochemical properties were studied to determine the band edge potentials and illustrate the enhanced photoresponse for heterojunction. The Bi 2 WO 6 /BiFeWO 6 heterojunction showed lower charge transfer resistance compared to Bi 2 WO 6 , owing to efficient charge separation at electrode-electrolyte interface. The synergistic effect of high surface area, lower recombination rate and the suitable band edge potentials led to high catalytic activity, good cycling stability and superior photoelectrochemical response of heterojunction. This work provide insight into the synergistic effect of hierarchical n-n heterojunction and opens up an avenue for rational design of photocatalyst for water splitting and H 2 generation. • The n-n Bi 2 WO 6 /BiFeWO 6 heterojunction has been developed • The photocatalytic H 2 generation of n-n Bi 2 WO 6 /BiFeWO 6 heterojunction is greatly enhanced. • The charge transfer mechanism are confirmed from Mott-Schottky analysis. • The synergistic effect of high surface area, lower recombination and suitable band edges led to high catalytic activity.

Synchronous synthesis of S-doped carbon nitride/nickel sulfide photocatalysts for efficient dye degradation and hydrogen evolution

Rational design of photocatalysts with low-cost and high-efficiency is of great significance for environmental remediation and energy utilization. Herein, the NiS-loaded on S-doped carbon nitride photocatalysts were synchronous synthesized via one-pot hydrothermal method. The activities of the photocatalysts were evaluated by photodegradation of RhB and photocatalytic hydrogen production under visible-light irradiation. It has been found that the optimal photocatalyst (SCN/NiS-1) showed outstanding photocatalytic activity of removing 98.5% RhB within 15 min and 700.9 μmol‧g−1‧h−1 H2-evolving rate with 0.89 wt% sulfur doping and 1 wt% NiS loading, respectively, which were significantly higher than pristine g-C3N4. The enhanced photocatalytic activity of SCN/NiS-1 was due to its expanded light absorption and facilitated separation or transportation of photoinduced charge carriers under the synergistic function of S doping and NiS loading. A possible mechanism of SCN/NiS-x on the improvement of the photocatalytic performance of carbon nitride was proposed based on a series of characterization analyses. This work strengthens the idea that bulk and surface engineering simultaneously affect photocatalytic activity.

High selective conversion of fructose to lactic acid by photocatalytic reforming of BiOBr/Znx@SnO2-n in alkaline condition

Herein, a novel p-n type BiOBr/Znx@SnO2-n photocatalyst was designed by using BiOBr coupling with large specific surface area Zn doped SnO2 through a facile in situ approach. The composite possesses proper redox potential as well as high efficiency interfacial charge transfer capability. Coupling BiOBr with Zn doped SnO2 is proved efficiency to form a facile bandgap regulation mechanism and could adjust the absorption capacity of visible light, thus enhances the photocatalytic performance effectively. The photocatalyst exhibits high efficiency in photo-reforming of fructose to lactic acid under alkaline conditions, achieving a maximum yield of 79.6% and still achieving a lactic acid yield of 70.7% even after five cycles of recycling. Possible pathways of the lactic acid production were proposed based on the generation of active oxidative radicals and the products detected during the reaction. Therefore, this work provides an effective approach for biomass conversion through rational photocatalyst design.

Biomass Photoreforming for Hydrogen Production over Hierarchical 3DOM TiO2-Au-CdS

Photocatalytic hydrogen production is a promising route to the provision of sustainable and green energy. However, the excess addition of traditional electron donors as the sacrificial agents to consume photogenerated holes greatly reduces the feasibility of this approach for commercialization. Herein, considering the abundant hydroxyl groups in cellulose, the major component of biomass, we adopted glucose (a component unit of cellulose), cellobiose (a structure unit of cellulose) and dissolving pulp (a pretreated cellulose) as electron donors for photocatalytic hydrogen production over a TiO2-Au-CdS material. The well-designed ternary TiO2-Au-CdS possesses a hierarchical three-dimensional ordered macroporous (3DOM) structure, which not only benefits light harvesting but can also facilitate mass diffusion to boost the reaction kinetics. As expected, the fabricated photocatalyst exhibits considerable hydrogen production from glucose (645.1 μmol·h−1·g−1), while the hydrogen production rates gradually decrease with the increased complexity in structure from cellobiose (273.9 μmol·h−1·g−1) to dissolving pulp (79.7 μmol·h−1·g−1). Other gaseous components such as CO and CH4 are also produced, indicating the partial conversion of biomass during the photoreforming process. This work demonstrates the feasibility of sustainable hydrogen production from biomass by photoreforming with a rational photocatalyst design.

In-situ constructed 2D/2D ZnIn2S4/Bi4Ti3O12 S-scheme heterojunction for degradation of tetracycline: Performance and mechanism insights

Semiconductor materials dominated photocatalytic technology is one of the most efficient approaches to degrade organic pollutants. However, the limited light absorption range and rapid recombination of photogenerated carriers greatly restrict the application of photocatalysts. Rational design of photocatalysts to achieve high catalytic activity and stability is of great importance. Herein, ZnIn2S4/Bi4Ti3O12 S-scheme heterojunction is synthesized by growing the ZnIn2S4 nanosheets on the sheet-like Bi4Ti3O12 surface via a low-temperature solvothermal method. The TC removal efficiency of optimized heterojunction reaches 82.1% within 60 min under visible light, and the rate constant is nearly 6.8 times than that of pristine ZnIn2S4. The favorable photocatalytic performance of heterojunction is attributed to the tight contact interface and efficient separation of photogenerated carriers. Besides, the difference in work function between ZnIn2S4 and Bi4Ti3O12 leads to band bending and the establishment of built-in electric field on the contact interface of heterojunction, which facilitates the migration and separation of photogenerated carriers. Furthermore, the cycling test demonstrates the attractive stability of heterojunction. The possible TC photodegradation pathways and toxicity assessment of the intermediates are also analyzed. In conclusion, this work provides an effective strategy to prepare S-scheme heterojunction photocatalysts with favorable photocatalytic activity, which can enhance wastewater purification efficiency.

Modifying electron injection kinetics for selective photoreduction of nitroarenes into cyclic and asymmetric azo compounds

Modifying the reactivity of substrates by encapsulation is essential for microenvironment catalysts. Herein, we report an alternative strategy that modifies the entry behaviour of reactants into the microenvironment and substrate inclusion thermodynamics related to the capsule to control the electron injection kinetics and the selectivity of products from the nitroarenes photoreduction. The strategy includes the orchestration of capsule openings to control the electron injection kinetics of electron donors, and the capsule’s pocket to encapsulate more than one nitroarene molecules, facilitating a condensation reaction between the in situ formed azanol and nitroso species to produce azo product. The conceptual microenvironment catalyst endows selective conversion of asymmetric azo products from different nitroarenes, wherein, the estimated diameter and inclusion Gibbs free energy of substrates are used to control and predict the selectivity of products. Inhibition experiments confirm a typical enzymatic conversion, paving a new avenue for rational design of photocatalysts toward green chemistry.

Fabrication of ultrathin lily-like NiCo2O4 nanosheets via mooring NiCo bimetallic oxide on waste biomass-derived carbon for highly efficient removal of phenolic pollutants

Rational design of photocatalysts with the controllable structure to expose active sites is crucial to degrade phenolic pollutants. Herein, we report the in-situ synthesis of lily-like NiCo2O4 nanosheets (0.95 nm) grown on waste biomass-derived carbon (abbreviated as NCC) for the highly efficient photocatalytic removal of phenolic pollutants through the integration of experiment and theory calculation. These as-fabricated NCC photocatalysts (2.29 nm) exhibit superior performance for the fast removal of phenolic pollutants (such as 4-Acetamidophenol (AP), phenol, and aspirin) in comparison with their counterpart and previously reported candidates. By using AP as a model molecule for mimicking pollutants, the photocatalytic degradation performance of NCC nanosheets is ∼ 1.3 and 1.9 times higher than that of pure NiCo2O4 (NC) and porous carbon, respectively. Various factors that influenced the degradation process such as peroxymonosulfate (PMS) concentration, catalyst dosage, AP concentration, and initial pH are thoroughly investigated. The free radical quenching experiments and electron paramagnetic resonance (EPR) spectra further demonstrate the existence of SO4−·, ·OH, ·O2–, and 1O2 in the reaction system and the ·O2– radical play a major role, which is also confirmed by the density functional theory (DFT) calculation. Several degradation pathways (e.g., demethylation, deacylation, hydroxylation, and ring-opening) are then proposed based on the detected intermediates. Finally, the high stability and good reusability of NCC nanosheets are confirmed via the degradation efficiency of over 85% even after five successive cycles.

Unraveling Charge‐Separation Mechanisms in Photocatalyst Particles by Spatially Resolved Surface Photovoltage Techniques

AbstractThe photocatalytic conversion of solar energy offers a potential route to renewable energy, and its efficiency relies on effective charge separation in nanostructured photocatalysts. Understanding the charge‐separation mechanism is key to improving the photocatalytic performance and this has now been enabled by advances in the spatially resolved surface photovoltage (SRSPV) method. In this Review we highlight progress made by SRSPV in mapping charge distributions at the nanoscale and determining the driving forces of charge separation in heterogeneous photocatalyst particles. We discuss how charge separation arising from a built‐in electric field, diffusion, and trapping can be exploited and optimized through photocatalyst design. We also highlight the importance of asymmetric engineering of photocatalysts for effective charge separation. Finally, we provide an outlook on further opportunities that arise from leveraging these insights to guide the rational design of photocatalysts and advance the imaging technique to expand the knowledge of charge separation.