Proton-Promoted Electron Transfer in Photocatalysis: Key Step for Photocatalytic Hydrogen Evolution on Metal/Titania Composites

Insights into the Dynamic Electron-Hole Separation Process Induced by a Trapped Electron in Lead Halide Perovskites in the Presence of Solutions

Metal halide perovskite solar cells show great promise, in terms of their high-power conversion efficiency. However, the dynamic electron-hole separation process remains elusive. Using ab initio molecular dynamics, we discover that the presence of photogenerated electron trapped at a Pb2+ ion can induce significant electron-hole separations on the CH3NH3PbI3 perovskite in the presence of HI solution. In this dynamic process, the separated electron is transferred to the Pb+ ion to form a Pb0 atom, while the separated hole is trapped in an I dimer. The reason behind this induced electron-hole separation is clearly revealed. Furthermore, the charge carrier transfer mechanism is elucidated, which not only explains the carrier migration but also the degradation of the perovskite in a humid environment. Comparing the atomic motions in CH3NH3PbI3 and CH3NH3PbCl3 quantitatively demonstrates that CH3NH3PbI3 is more active but less stable than CH3NH3PbCl3. The proposed mechanism for the electron-hole separation mechanism and perovskite degradation in humid conditions provides insights into the design of a highly efficient perovskite with good stability.

Enzyme-Photocoupled Catalytic Systems Based on Zirconium-Metal-Organic Frameworks

Green, low-carbon, and efficient chemical conversions are crucial for the sustainable development of modern society. Enzyme-photocoupled catalytic systems (EPCS), which mimic natural photosynthesis, utilize solar energy to drive biochemical reactions, providing emergent opportunities to address the limitations of traditional photocatalytic systems. However, the integration and compatibility of photocatalysis and biocatalysis present challenges in designing highly efficient and stable EPCS. Zirconium-based metal-organic frameworks (Zr-MOFs) with outstanding chemical and thermal stability, large surface area, and tunable pore size are ideal candidates for supporting enzymes and enhancing photocatalytic processes. This review aims to integrate Zr-MOFs with EPCS to further promote the development of EPCS. First, an overview of the basic components and design principles of EPCS is provided, highlighting the importance of the unique properties of Zr-MOFs. After that, three different strategies for combining enzymes with Zr-MOFs are summarized and their respective advantages are evaluated. Finally, the development opportunities and some problems to be solved in this field are proposed.

Effects of surface oxygen vacancy on CO2 adsorption and its activation towards C2H4 using metal (Cu, Pd, CuPd) cluster-loaded TiO2 catalysts: a first principles study

The conversion of the highly selective CO2 reduction reaction (CO2RR) into desired value-added multicarbon compounds, like C2H4, is crucial, but it is mainly constrained by the high energy barrier for C-C coupling and the multi-electron transfer process. Herein, M/TiO2 and M/TiO2-VO (M = Cu, Pd, CuPd, and VO refers to the surface oxygen vacancy) catalysts were designed to study the CO2RR towards C2H4 by using density functional theory (DFT). We found that the surface oxygen vacancy enhances the adsorption ability of studied catalysts. The CO2 molecule is strongly adsorbed at the metal-surface interfaces of Cu/TiO2-VO, Pd/TiO2-VO and CuPd/TiO2-VO catalysts with adsorption energies of -1.79, -1.75 and -1.71 eV, respectively. Furthermore, the C-C coupling reaction does not occur on the Cu and PdCu cluster sites of the M/TiO2-VO catalysts, indicating the inactivity of these sites for C2 products. However, Pd/TiO2, CuPd/TiO2 and M/TiO2-VO interfaces favor the C-C coupling reaction and therefore have the potential to reduce CO2 to C2 products. Additionally, the Gibbs free energy calculations reveal that the surface oxygen vacancy improves the OCCO hydrogenation to C2H4 at the CuPd/TiO2-VO interface.

Clarifying the Direct Generation of •OH Radicals in Photocatalytic O2 Reduction: Theoretical Prediction Combined with Experimental Validation

This work systematically studied thermocatalytic and photocatalytic pathways of formaldehyde degradation and H-assisted O2 reduction over a Pt13/anatase-TiO2(101) composite via DFT calculations together with constrained molecular dynamics (MD) simulations. We show that photocatalytic O2 reduction on Pt/TiO2 can directly generate •OH radicals (*O2 → *OOH → •OH) via two hydrogenation steps with small barriers, and the product selectivity (*H2O2 or •OH) is decided by the relative position between catalyst Fermi level and •OH/*H2O2 redox potential (theoretical determination of 0.07 V referencing to the SHE). Such a novel reaction channel was furthermore validated at the liquid-solid interface via constrained MD simulations and experimental electron paramagnetic resonance detections, and a wide range of H resources, e.g., *HCHO, *HCO, *H (H+ + e-), can always drive the direct •OH generation. The additional portion of e--triggered •OH radicals are prone to diffuse into solution or the TiO2 surface and furthermore cooperate with the conventional h+-driven photooxidations.

Excitonic Effects of the Excited-State Photocatalytic Reaction at the Molecule/Metal Oxide Interface

Excitonic effects caused by the Coulomb interaction between electrons and holes play a crucial role in photocatalysis at the molecule/metal oxide interface. As an ideal model for investigating the excitonic effect, coadsorption and photodissociation of water and methanol molecules on titanium dioxide involve complex ground-state thermalcatalytic and excited-state photocatalytic reaction processes. Herein, we systemically investigate the excited-state electronic structures of the coadsorption of H2O and CH3OH molecules on a rutile TiO2(110) surface by linear-response time-dependent density functional theory calculations and probe the reaction path for generating HCOOH or CO2, from ground-state and excited-state perspectives. The reaction barriers in excited-state calculations are significantly different from those in ground-state calculations during three processes, with the largest decrease being 0.94 eV for the Ti5c-O-CH2-O-Ti5c formation process.

Highly Selective Tandem Photoelectrochemical C-H Activation via Bromine Evolution Reaction in Two-Phase Electrolyte

The development of environmentally friendly and safe chemical processes using renewable energy sources is important. In this study, a photoelectrochemical (PEC) cell was used for the tandem bromination of sp3 carbon within a unique two-phase electrolyte system. By incorporation of a RuOx cocatalyst, the Ta3N5 photoelectrode demonstrated a remarkable selectivity for Br2 close to 100%. The kinetic study for charge carriers of photoelectrodes reveals that the improved charge transfer at Ta3N5/RuOx interfaces contributed to excellent photoelectrochemical Br2 evolution activity. The photoelectrochemically produced Br2 was utilized for bromination of α-sp3 carbon in toluene, 1-methylnaphthalene, ethylbenzene, or cyclohexane by the Ta3N5/RuOx photoanode with 100% regioselectivity. The coupling of the Ta3N5 photoanode and InP photocathode generated H2 and Br2 under light illumination without external bias. This study provides systematic insights into the design of photoelectrodes for solar-driven tandem bromination systems within the unique environment of a two-phase electrolyte system.

Metal Clusters Based Multifunctional Materials for Solar Cells

As a multifunctional material, metal clusters have recently received some attention for their application in solar cells.This review delves into the multifaceted role of metal clusters in advancing solar cell technologies, covering diverse aspects from electron transport and interface modification to serving as molecular precursors for inorganic materials and acting as photosensitizers in metal-cluster sensitized solar cells (MCSSCs). The studies conducted by various researchers illustrate the crucial impact of metal clusters, such as gold nanoclusters (Au NCs), on enhancing solar cell efficiency through size-dependent effects, distinct interface behaviors, and tailored interface engineering. From optimizing charge transfer rates to improving light absorption and reducing carrier recombination, metal clusters prove instrumental in shaping the landscape of solar energy conversion.The promising performance of metal-cluster sensitized solar cells, coupled with their scalability and flexibility, positions them as a exciting avenue for future clean energy applications. The article concludes by emphasizing the need for continued interdisciplinary research and technological innovation to unlock the full potential of metal clusters in contributing to sustainable and high-performance solar cells.

Green electrosynthesis of 3,3'-diamino-4,4'-azofurazan energetic materials coupled with energy-efficient hydrogen production over Pt-based catalysts

The broad employment of clean hydrogen through water electrolysis is restricted by large voltage requirement and energy consumption because of the sluggish anodic oxygen evolution reaction. Here we demonstrate a novel alternative oxidation reaction of green electrosynthesis of valuable 3,3'-diamino-4,4'-azofurazan energetic materials and coupled with hydrogen production. Such a strategy could greatly decrease the hazard from the traditional synthetic condition of 3,3'-diamino-4,4'-azofurazan and achieve low-cell-voltage hydrogen production on WS2/Pt single-atom/nanoparticle catalyst. The assembled two-electrode electrolyzer could reach 10 and 100 mA cm-2 with ultralow cell voltages of 1.26 and 1.55 V and electricity consumption of only 3.01 and 3.70 kWh per m3 of H2 in contrast of the conventional water electrolysis (~5 kWh per m3). Density functional theory calculations combine with experimental design decipher the synergistic effect in WS2/Pt for promoting Volmer-Tafel kinetic rate during alkaline hydrogen evolution reaction, while the oxidative-coupling of starting materials driven by free radical could be the underlying mechanism during the synthesis of 3,3'-diamino-4,4'-azofurazan. This work provides a promising avenue for the concurrent electrosynthesis of energetic materials and low-energy-consumption hydrogen production.

Advancing nitrate reduction to ammonia: insights into mechanism, activity control, and catalyst design over Pt nanoparticle-based ZrO2

The reduction of nitrogen oxides (NOx) to NH3, or N2 represents a crucial step in mitigating atmospheric NO3 and NO2 emissions, a significant contributor to air pollution. Among these reduction products, ammonia (NH3) holds particular significance due to its utility in nitrogen-based fertilizers and its versatile applications in various industrial processes. Platinum-based catalysts have exhibited promise in enhancing the rate and selectivity of these reduction reactions. In this study, we employ density functional theory (DFT) calculations to explore the catalytic potential of Pt nanoparticle (PtNP)-supported ZrO2 for the conversion of NO3 to NH3. The most favorable pathway for the NO3 reduction to NH3 follows a sequence, that is, NO3 → NO2 → NO → ONH → ONH2/HNOH → NH2/NH → NH2 → NH3, culminating in the production of valuable ammonia. The introduction of low-state Fe and Co dopants into the ZrO2 support reduces energy barriers for the most challenging rate-determining hydrogenation step in NOx reduction to NH3, demonstrating significant improvements in catalytic activity. The incorporation of dopants into the ZrO2 support results in a depletion of electron density within the Pt cocatalyst resulting in enhanced hydrogen transfer efficiency during the hydrogenation process. This study aims to provide insights into the catalytic activity of platinum-based ZrO2 catalysts and will help design new high-performance catalysts for the reduction of atmospheric pollutants and for energy applications.

Coordinating Interface Polymerization with Micelle Mediated Assembly Towards Two-Dimensional Mesoporous Carbon/CoNi for Advanced Lithium-Sulfur Battery

Lithium-sulfur battery has attracted significant attention by virtues of their high theoretical energy density, natural abundance, and environmental friendliness. However, the notorious shuttle effect of polysulfides intermediates severely hinders its practical application. Herein, a novel 2D mesoporous N-doped carbon nanosheet with confined bimetallic CoNi nanoparticles sandwiched graphene (mNC-CoNi@rGO) is successfully fabricated through a coordinating interface polymerization and micelle mediated co-assembly strategy. mNC-CoNi@rGO serves as a robust host material that endows lithium-sulfur batteries with a high reversible capacity of 1115 mAh g^-1 at 0.2 C after 100 cycles, superior rate capability, and excellent cycling stability with 679.2 mAh g^-1 capacity retention over 700 cycles at 1 C. With sulfur contents of up to 5.0 mg cm^-2 , the area capacity remains to be 5.1 mAh cm^-2 after 100 cycles at 0.2 C. The remarkable performance is further resolved via a series of experimental characterizations combined with density functional theory calculations. These results reveal that the ordered mesoporous N-doped carbon-encapsulated graphene framework acts as the ion/electron transport highway with excellent electrical conductivity, while bimetallic CoNi nanoparticles enhance the polysulfides adsorption and catalytic conversion that simultaneously accelerate the multiphase sulfur/polysulfides/sulfides conversion and inhibit the polysulfides shuttle.

Insights of Fe2O3 and MoO3 Electrodes for Electrocatalytic CO2 Reduction in Aprotic Media

Transition metal oxides (TMO) have been successfully used as electrocatalytically active materials for CO2 reduction in some studies. Because of the lack of understanding of the catalytic behavior of TMOs, electrochemical methods are used to investigate the CO2 reduction in thin-film nanostructured electrodes. In this context, nanostructured thin films of Fe2O3 and MoO3 in an aprotic medium of acetonitrile have been used to study the CO2 reduction reaction. In addition, a synergistic effect between CO2 and the TMO surface is observed. Faradic cathodic processes not only start at lower potentials than those reported with metal electrodes, but also an increase in capacitive currents is observed, which is directly related to an increase in oxygen vacancies. Finally, the results obtained show CO as a product of the reduction.

Recognition of Water-Induced Double-Edged Sword Effects in Photocatalytic Selective Oxidation of Toluene on Titanium Dioxide Clusters with Density Functional Theory Calculations

Recently, water promotion effects in the selective oxidation of benzyl alcohol to benzaldehyde have been experimentally recognized and identified. However, the effects of water on the photocatalytic selective oxidation of toluene into benzaldehyde remain elusive. In this work, the Ti₃O₉H₆ clusters in different solvents (water and toluene solvent) are used to study the water-induced effects in photocatalytic oxidation reactions in kinetics and thermodynamics using density functional theory (DFT) calculations. In addition, the influences of the OH groups on catalysts (Ti-OH bonds) from photocatalytic water splitting are also considered. The results clearly demonstrate the water-induced double-edged sword effects in the photocatalytic selective oxidation of toluene. We expect that our work can not only shed light on the mechanisms of photocatalytic selective oxidation of toluene into benzaldehyde and other activation reactions of sp³ C-H bonds but also design and modulate highly efficient photocatalysts.

Addressing Dynamics at Catalytic Heterogeneous Interfaces with DFT-MD: Anomalous Temperature Distributions from Commonly Used Thermostats

Density functional theory-based molecular dynamics (DFT-MD) has been widely used for studying the chemistry of heterogeneous interfacial systems under operational conditions. We report frequently overlooked errors in thermostated or constant-temperature DFT-MD simulations applied to study (electro)catalytic chemistry. Our results demonstrate that commonly used thermostats such as Nosé-Hoover, Berendsen, and simple velocity-rescaling methods fail to provide a reliable temperature description for systems considered. Instead, nonconstant temperatures and large temperature gradients within the different parts of the system are observed. The errors are not a "feature" of any particular code but are present in several ab initio molecular dynamics implementations. This uneven temperature distribution, due to inadequate thermostatting, is well-known in the classical MD community, where it is ascribed to the failure in kinetic energy equipartition among different degrees of freedom in heterogeneous systems (Harvey et al. J. Comput. Chem. 1998, 726-740) and termed the flying ice cube effect. We provide tantamount evidence that interfacial systems are susceptible to substantial flying ice cube effects and demonstrate that the traditional Nosé-Hoover and Berendsen thermostats should be applied with care when simulating, for example, catalytic properties or structures of solvated interfaces and supported clusters. We conclude that the flying ice cube effect in these systems can be conveniently avoided using Langevin dynamics.

Efficient Photoinduced Electron Transfer from Pyrene-o-Carborane Heterojunction to Selenoviologen for Enhanced Photocatalytic Hydrogen Evolution and Reduction of Alkynes

A series of pyrene or pyrene-o-carborane-appendant selenoviologens (Py-SeV²⁺ , Py-Cb-SeV²⁺ ) for enhanced photocatalytic hydrogen evolution reaction (HER) and reduction of alkynes is reported. The efficient photoinduced electron transfer (PET) from electron-rich pyrene-o-carborane heterojunction (Py-Cb) with intramolecular charge transfer (ICT) characteristic to electron-deficient selenoviologen (SeV²⁺ ) (k_ET = 1.2 × 10¹⁰ s^-1 ) endows the accelerating the generation of selenoviologen radical cation (SeV^+• ) compared with Py-SeV²⁺ and other derivatives. The electrochromic/electrofluorochromic devices' (ECD and EFCD) measurements and supramolecular assembly/disassembly processes of SeV²⁺ and cucurbit[8]uril (CB[8]) results show that the PET process can be finely tuned by electrochemical and host-guest chemistry methods. By combination with Pt-NPs catalyst, the Py-Cb-SeV²⁺ -based system shows high-efficiency visible-light-driven HER and highly selective phenylacetylene reduction due to the efficient PET process.

Theoretical and experimental studies of high efficient all-solid Z-scheme TiO2-TiC/g-C3N4 for photocatalytic CO2 reduction via dry reforming of methane

All-solid Z-scheme heterojunction TiO2-TiC/g-C3N4 was proposed and synthesized successfully by a facile calcination method and used for photocatalytic CO2 reduction in the presence of CH4. Under sub-atmospheric pressure and room...

Oxygen vacancy and nitrogen doping collaboratively boost performance and stability of TiO2-supported Pd catalysts for CO2 photoreduction: a DFT study

The regulation of interfacial charge transfer, optimization of active sites, and maintenance of stability are effective strategies for improving catalytic performance. The effect of the oxygen vacancy (V_O) and nitrogen doping on these parameters for CO₂ photoreduction on Pd₁₀/TiO₂(101) was studied using density functional theory calculations. The results demonstrate that introduction of the V_O could trigger reversed electron transfer, making the V_O and Pd atoms the active center for CO₂ reduction. However, the V_O is repaired by the dissociated O atom. The combined effect of the V_O and N is related to the position of N. Although the substitutional N (N_S) can delocalize electrons at the V_O, it cannot improve the activity and stability. The interstitial N (N_i) located below the V_O forms N_i-Ti bonds with two Ti atoms adjacent to the V_O. This can delocalize the electrons near the V_O, and the five-fold-coordinated titanium (Ti_5C) replaces the V_O as the active center, thus enhancing the reactivity and protecting the V_O. Further research indicates that the co-modification of the V_O and N_i improves photoexcited electron transfer and distribution, which would in turn promote CO₂ reduction. The results of this study propose that surface defect engineering holds great promise for boosting CO₂ photoreduction by integrating functions of electron density modulation and catalysis.

Hydrogen Coupling on Platinum Using Artificial Neural Network Potentials and DFT

To date, the understanding of reactions at solid-liquid interfaces has proven challenging, mainly because of the inaccessible nature of such systems to current experimental techniques with atomic resolution. This has meant that many important features, including free energy barriers and the atomistic structure of intermediates, remain unknown. To tackle these issues, we construct and utilize a high-dimensional neural network (HDNN) potential for the simulation of hydrogen evolution at the HCl(aq)/Pt(111) interface, taking into consideration the influence of adsorbate-adsorbate, adsorbate-solvent interactions, and ion solvation explicitly. Long time scale MD simulations reveal coadsorbed H_ad/H₂O_ad on the surface. The free energy profiles for the Tafel and Heyrovsky type hydrogen coupling are extracted using umbrella sampling. It is found that the preferential mechanism can change depending on the surface coverage, highlighting the dual mechanistic nature for HER on Pt(111). Our work demonstrates the importance of controlling the solvent-substrate interactions in developing catalysts beyond Pt.

Subtle structure matters: boosting surface-directed photoelectron transfer via the introduction of specific monovalent oxygen vacancies in TiO2

Oxygen vacancies (O_v) are widely considered to play crucial roles in photocatalysis, but how and why they contribute to improved performances remains controversial. In this work, we studied the promotional effect of O_v on photoelectron transfer in TiO₂, using first-principles density functional theory calculations with correction for on-site Coulomb interactions. We explicitly identified three types of O_v with different charge states (i.e., charge-neutral , monovalent , divalent O_v²⁺) via electronic structure analysis. Electron transfer energy calculations revealed that the ionized O_v in anatase TiO₂ are able to collect excess electrons whereas those in the rutile phase are not. The presence of ionized O_v further endows anatase TiO₂ with directional electron transfer along the [100] orientation, in favor of anatase TiO₂(101) for photocatalytic reduction surpassing the (001) termination. After examining various combination modes of ionized O_v involving different charge states and spatial distributions, we demonstrated that the vertical chain in anatase TiO₂(101) is the most catalytically effective O_v pattern in TiO₂. These results signify the importance of subtle defects in photocatalysis and may assist future photocatalyst design toward higher photocatalytic efficiency.

Metal-facilitated Photocatalytic Nanohybrids: Rational Design and Promising Environmental Applications

As a promising technique to potentially address the energy crisis and environmental issues, photocatalysis has been reported widely to exhibit various outstanding behaviors in production of new fuels/chemicals and treatment of contaminants. The photocatalytic performance is extremely dependent on the used photocatalysts, so that the design and preparation of efficient photocatalysts are critically important for significantly improving the photocatalytic activity. Among various strategies, the hybridization of metal with semiconductors has recently been attracting more and more research interest owing to their expended spectral absorption, promoted transferring rate of charge carriers and Plasmon-enhanced effect. In this minireview, the metal-facilitated hybrid photocatalysts are overviewed comprehensively to first reveal unique functions of metals in improvement of photoactivity and summarize the emerging metal-involved hybrid systems. Subsequently, the synthetic methods towards hybrid photocatalysts are introduced and their practical applications are emphasized in environmental remediation including degradation of organic pollutants, conversion of harmful gases, treatment of heavy metal ions and sterilization of bacteria. At the end, the challenges for industrializing these hybrid photocatalysts are discussed carefully and future development is suggested rationally.

Function-oriented design of robust metal cocatalyst for photocatalytic hydrogen evolution on metal/titania composites

While the precise design of catalysts is one of ultimate goals in catalysis, practical strategies often fall short, especially for complicated photocatalytic processes. Here, taking the hydrogen evolution reaction (HER) as an example, we introduce a theoretical approach for designing robust metal cocatalysts supported on TiO₂ using density functional theory calculations adopting on-site Coulomb correction and/or hybrid functionals. The approach starts with clarifying the individual function of each metal layer of metal/TiO₂ composites in photocatalytic HER, covering both the electron transfer and surface catalysis aspects, followed by conducting a function-oriented optimization via exploring competent candidates. With this approach, we successfully determine and verify bimetallic Pt/Rh/TiO₂ and Pt/Cu/TiO₂ catalysts to be robust substitutes for conventional Pt/TiO₂. The right metal type as well as the proper stacking sequence are demonstrated to be key to boosting performance. Moreover, we tentatively identify the tunneling barrier height as an effective descriptor for the important electron transfer process in photocatalysis on metal/oxide catalysts. We believe that this study pushes forward the frontier of photocatalyst design towards higher water splitting efficiency.

Unraveling the Photogenerated Electron Localization on the Defect-Free CH3NH3PbI3(001) Surfaces: Understanding and Implications from a First-Principles Study

The localization of photogenerated electrons in photovoltaic and photocatalytic materials is crucial for reducing the electron-hole recombination rate. Here, the photogenerated electron localization is systematically investigated on the CH₃NH₃PbI₃ (MAPbI₃) perovskite using first-principles calculations. It is found that under vacuum conditions, the photogenerated electron is delocalized in the MAPbI₃ bulk as well as on the stochiometric MAPbI₃(001) surface with the CH₃NH₃I (MAI) termination, while it is trapped on the defect-free PbI₂-terminated surface. Our ab initio molecular dynamics simulations reveal that the introduction of solutions will prompt the formation of localized electronic states. The photogenerated electron is discovered to be localized on both the MAI- and PbI₂-terminated surfaces in the presence of solutions with different concentrations of HI, from pure water to the saturated solution. We demonstrate that the Pb-I bond weakening or breaking resulting in an unsaturated coordination of a Pb site is the prerequisite to trap the photogenerated electron.

Proton-assisted electron transfer and hydrogen-atom diffusion in a model system for photocatalytic hydrogen production

Solar energy can be converted into chemical energy by photocatalytic water splitting to produce molecular hydrogen. Details of the photo-induced reaction mechanism occurring on the surface of a semiconductor are not fully understood, however. Herein, we employ a model photocatalytic system consisting of single atoms deposited on quantum dots that are anchored on to a primary photocatalyst to explore fundamental aspects of photolytic hydrogen generation. Single platinum atoms (Pt₁) are anchored onto carbon nitride quantum dots (CNQDs), which are loaded onto graphitic carbon nitride nanosheets (CNS), forming a Pt₁@CNQDs/CNS composite. Pt₁@CNQDs/CNS provides a well-defined photocatalytic system in which the electron and proton transfer processes that lead to the formation of hydrogen gas can be investigated. Results suggest that hydrogen bonding between hydrophilic surface groups of the CNQDs and interfacial water molecules facilitates both proton-assisted electron transfer and sorption/desorption pathways. Surface bound hydrogen atoms appear to diffuse from CNQDs surface sites to the deposited Pt₁ catalytic sites leading to higher hydrogen-atom fugacity surrounding each isolated Pt₁ site. We identify a pathway that allows for hydrogen-atom recombination into molecular hydrogen and eventually to hydrogen bubble evolution.

A Ti-MOF Decorated With a Pt Nanoparticle Cocatalyst for Efficient Photocatalytic H2 Evolution: A Theoretical Study

Pt nanoparticles (NPs) are often used as cocatalysts to enhance the photocatalytic hydrogen production catalyzed by the metal organic framework (MOF) materials. The catalytic efficiency of many Pt/MOF systems can be greatly improved when Pt NPs are used as cocatalysts. In this work, the Pt/20%-MIL-125-(SCH₃)₂ was chosen as the template material to understand the functional role of a Pt metal cocatalyst in the catalytic process. Experimentally, the catalytic activity of Pt/20%-MIL-125-(SCH₃)₂ is more than 100 times that of the system without the help of Pt NPs. Firstly, we proposed a searching algorithm, which is based on the combined Monte Carlo (MC) method and principal component analysis (PCA) algorithm, to find that the most probable adsorption site of the Pt₁₃ nanocluster loaded on the (001) surface of 20%-MIL-125-(SCH₃)₂. Next, by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we revealed that the accumulation of some positive charges on the Pt₁₃ cluster and proton adsorbed on the Pt₁₃ cluster, which can promote the separation of photogenerated electrons and holes, thus improving the photocatalytic efficiency. This work not only provides a method to obtain the adsorption configuration of metal clusters on various MOFs but also provides a new insight into increasing photocatalytic efficiency for H₂ production in Pt/MOF systems.

Dewetting of PtCu Nanoalloys on TiO2 Nanocavities Provides a Synergistic Photocatalytic Enhancement for Efficient H2 Evolution

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H₂ evolution from methanol-water solutions. To produce the photocatalysts, a few-nanometer-thick Pt-Cu bilayers are deposited on anodic TiO₂ nanocavity arrays and converted by solid-state dewetting via a suitable thermal treatment into bimetallic PtCu nanoparticles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results prove the formation of PtCu nanoalloys that carry a shell of surface oxides. X-ray absorption near-edge structure (XANES) data support Pt and Cu alloying and indicate the presence of lattice disorder in the PtCu nanoparticles. The PtCu co-catalyst on TiO₂ shows a synergistic activity enhancement and a significantly higher activity toward photocatalytic H₂ evolution than Pt- or Cu-TiO₂. We propose the enhanced activity to be due to Pt-Cu electronic interactions, where Cu increases the electron density on Pt, favoring a more efficient electron transfer for H₂ evolution. In addition, Cu can further promote the photoactivity by providing additional surface catalytic sites for hydrogen recombination. Remarkably, when increasing the methanol concentration up to 50 vol % in the reaction phase, we observe for PtCu-TiO₂ a steeper activity increase compared to Pt-TiO₂. A further increase in methanol concentration (up to 80 vol %) causes for Pt-TiO₂ a clear activity decay, while PtCu-TiO₂ still maintains a high level of activity. This suggests improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO.

Site dependent reactivity of Pt single atoms on anatase TiO2(101) in an aqueous environment

The TiO₂-Pt-water interface is of great relevance in photocatalysis where Pt is widely used as a co-catalyst for enhancing hydrogen evolution in aqueous TiO₂. Using ab initio molecular dynamics, we investigated this interface focusing on Pt single atoms supported on anatase TiO₂(101) in a water environment. Based on recent experiments showing a broad distribution of Pt coordination sites in TiO₂, we examined six distinct single-Pt supported species with different nominal Pt oxidation states, namely: Pt, PtOH, and PtO₂ species adsorbed on the stoichiometric surface; Pt adsorbed at a surface oxygen vacancy (O_v); and Pt substituting a surface Ti cation (Pt_Ti), both without and with an accompanying O_v (Pt_Ti + O_v). As found for the pristine anatase surface, interfacial water remained intact in the presence of a nearly neutral Pt adatom within the time duration of our simulations (∼15 ps). Similarly, no (or only temporary) water dissociation was observed at the Pt_Ti + O_v and PtO₂ interfaces, due to the formation of very stable planar Pt coordination structures that interact only weakly with water. In contrast, water dissociated with OH^- (H⁺) on the Pt atom when this substituted a surface Ti (oxygen) ion as well as on PtOH. The significant proton affinity of Pt atoms at surface oxygen vacancies suggests that negatively charged Pt species are particularly efficient at catalyzing hydrogen evolution in aqueous TiO₂.

Photo/electrocatalysis and photosensitization using metal nanoclusters for green energy and medical applications

Owing to the rapidly increasing demand for sustainable technologies in fields such as energy, environmental science, and medicine, nanomaterial-based photo/electrocatalysis has received increasing attention. Recently, synthetic innovations have allowed the fabrication of atomically precise metal nanoclusters (NCs). These NCs show potential for green energy and medical applications. The present article primarily focuses on evaluation of the recent developments in the photo/electrocatalytic and photosensitizing characteristics of metal and alloy NCs. The review comprises two sections: (i) photo/electrocatalysis for green energy and (ii) photosensitization for biomedical therapy applications. Finally, the challenges associated with the use of metal NCs are presented on the basis of current developments.

Identifying the role of excess electrons and holes for initiating the photocatalytic dissociation of methanol on a TiO2(110) surface

As a prototype for the catalytic oxidation of organic contaminants, photocatalytic methanol dissociation on rutile TiO₂(110) has drawn much attention, but its reaction mechanism remains elusive.

Understanding supported noble metal catalysts using first-principles calculations

Heterogeneous catalysis on supported and nonsupported nanoparticles is of fundamental importance in the energy and chemical conversion industries. Rather than laboratory analysis, first-principles calculations give us an atomic-level understanding of the structure and reactivity of nanoparticles and supports, greatly reducing the efforts of screening and design. However, unlike catalysis on low index single crystalline surfaces, nanoparticle catalysis relies on the tandem properties of a support material as well as the metal cluster itself, often with charge transfer processes being of key importance. In this perspective, we examine current state-of-the-art quantum-chemical research for the modeling of reactions that utilize small transition metal clusters on metal oxide supports. This should provide readers with useful insights when dealing with chemical reactions on such systems, before discussing the possibilities and challenges in the field.

Mitigation of harmful indoor organic vapors using plug-flow unit coated with 2D g-C3N4 and metallic Cu dual-incorporated 1D titania heterostructure

Herein, a plug-flow reactor coated with one-dimensional (1D) TiO₂ nanotube (TNT) heterostructures incorporated with g-C₃N₄ (CN) and metallic Cu (CN/Cu/TNT) nanocomposite and irradiated by a daylight lamp was newly applied for the mitigation of harmful indoor organic vapors. The CN/Cu/TNT catalyst showed high mitigation efficiency for all target pollutants, followed by Cu-incorporated TNT (Cu/TNT), CN-incorporated TNT (CN/TNT), TNT, and TiO₂, in that order. The order of their photocatalytic activities agrees with that of the electron‒hole separation rates determined from their photoluminescence emission spectra. The mitigation efficiency of the CN/Cu/TNT catalyst increased as the CN-to-Cu/TNT percentage was increased from 1% to 10%, but subsequently decreased as the CN-to-Cu/TNT percentage increased to 20%. The mitigation efficiencies of the CN/Cu/TNT catalyst decreased with increasing relative humidity, feed pollutant concentrations, and airstream flow rates. However, in most cases, the reaction rates of the target compounds increased when the feed concentration was increased from 1 to 5 ppm. The mineralization rates of all target pollutants were lower than the corresponding photocatalytic mitigation rates, which could be ascribed to the production of CO and organic intermediates observed during the photocatalysis of the target pollutants. Nevertheless, the intermediates formed during the photocatalytic mitigation process would not cause significant adverse health effects to building occupants, because their concentrations were far below their exposure or threshold limit values. A probable mechanism for the photocatalytic mitigation of the organic vapors by the CN/Cu/TNT catalyst under daylight illumination was also proposed.