Metal Cocatalysts Research Articles

Se–Se bonds induced highly metallic 1T’ MoSe2.3 nanosheets cocatalysts towards boosted H2O2 photosynthesis over NH2-MIL-125 derived TiO2 nanotablets

Loading non-noble metal cocatalysts is a promising means to inhibit the photogenerated charge recombination and provide more active centers for surface photocatalytic reactions, especially for hydrogen peroxide (H2O2) generation. The H2O2 photosynthesize activity has shown to be seriously limited by secondary decomposition of synthesized H2O2, owing to the presence of metal-based active centers. Herein, highly metallic MoSe2.3 nanosheet with dominated 1T and 1T' phase were in-situ loaded onto the NH2-MIL-125(Ti) derived TiO2 nanotablets via a one-step hydrothermal method to form a TiO2/MoSe2.3 composite for enhancing photocatalytic H2O2 production activity. The abundant edge Se–Se bonds, along with the high content of 1T and 1T' phase endowed MoSe2.3 nanosheets with highly metallic property to function as an efficient cocatalyst to accelerate the carrier separation. Besides that, Se–Se bonds could offer more active centers for O2 adsorption to boost the generation of H2O2. As a result, the optimal TiO2/MoSe2.3 composite photocatalyst (TM-5) displayed a much enhanced H2O2 production performance of 891 µmol L–1 h−1 in isopropanol solution (IPA, 10 vol.%) under monochrome LED-(365 nm) light irradiation, 2.3 times higher than pure NH2-MIL-125 derived TiO2 nanotablets. This work would provide a feasible method in non-metal cocatalyst design for H2O2 photosynthesize.

P-N Heterojunction Embedded CuS/TiO2 Bifunctional Photocatalyst for Synchronous Hydrogen Production and Benzylamine Conversion.

The coupling of photocatalytic hydrogen production and selective oxidation of benzylamine is a topic of significant research interest. However, enhancing the bifunctional photocatalytic activity in this context is still a major challenge. The construction of Z-scheme heterojunctions is an effective strategy to enhance the activity of bifunctional photocatalysts. Herein, a p-n type direct Z-scheme heterojunction CuS/TiO2 is constructed using metal-organic framework (MOF)-derived TiO2 as a substrate. The carrier density is measured by Mott-Schottky under photoexcitation, which confirms that the Z-scheme electron transfer mode of CuS/TiO2 is driven by the diffusion effect caused by the carrier concentration difference. Benefiting from efficient charge separation and transfer, photogenerated electrons, and holes are directedly transferred to active oxidation and reduction sites. CuS/TiO2 also exhibits excellent bifunctional photocatalytic activity without noble metal cocatalysts. Among them, the H2 evolution activity of the CuS/TiO2 is found to be 17.1 and 29.5 times higher than that of TiO2 and CuS, respectively. Additionally, the yields of N-Benzylidenebenzylamine (NBB) are 14.3 and 47.4 times higher than those of TiO2 and CuS, respectively.

Enhanced photocatalytic reaction activity of Cu2WS4/Ag2S composite photocatalyst

Coupling noble metal cocatalysts are considered to be one of the most effective approaches to improve photocatalytic performance, but their expensive price limits their practical application. Herein, a series of Cu2WS4/Ag2S nanocomposite photocatalysts were successfully synthesized by a simple ion exchange method using Ag2S as the cocatalyst. Compared with pure Cu2WS4 and Ag2S, the optimized 25 wt% Cu2WS4/Ag2S (CA25) nanocomposites exhibited excellent photocatalytic degradation capability of RhB (96 %,20 min). More importantly, the as-prepared CA25 sample showed a significant photocatalytic hydrogen yield (19.8 μmol/h), which is 9.4 times that of pure Cu2WS4. Systematic studies revealed that the introduction of Ag2S can not only broaden the light absorbance capacity of the composite photocatalyst, but also effectively improve the separation efficiency of the photogenerated carriers. In addition, our results showed that photogenerated electrons simultaneously reduce Ag2S into metallic Ag in the photocatalytic reaction process, that is, metallic Ag can act as the bridge to capture electrons and accelerate the transmission of photogenerated carriers, thus enabling further enhancement of photocatalytic performance. This work provides a new insight for the design of highly efficient composite photocatalysts, and highlights the important role of photocarrier separation in the photocatalytic process.

Promoted Photocatalytic Hydrogen Evolution by Tuning the Electronic State of Copper Sites in Metal‐Organic Supramolecular Assemblies

AbstractThe electronic state in terms of charge and spin of metal sites is fundamental to govern the catalytic activity of a photocatalyst. Herein, we show that modulation of the electronic states of Cu sites, without changing the coordination environments, of two metal‐organic supramolecular assemblies based on π⋅⋅⋅π stacking can significantly improve photocatalytic activity. The use of these heterogeneous photocatalysts, without using noble metal cocatalysts, resulted in an increase of the hydrogen production rate from 522 to 3620 μmol h−1 g−1. A systematical analysis revealed that the charge density and spin density of the metal centers are efficiently modulated via the modulation of the coordination fields around active copper (II) centers by the variation of the non‐coordination groups of terminal ligands, leading to the significant enhancement of photocatalytic activity. This work provides an insight into the electronic state of active metal centers for designing high‐performance photocatalysts.

The effect of Ni and Co co-catalysts on the catalytic activity of mesoporous graphitic carbon nitride/black phosphorus/molybdenum disulfide heterojunctions in solar-driven hydrogen evolution

In this work, a ternary heterojunction photocatalyst composed of mesoporous graphitic carbon nitride, black phosphorus, and molybdenum disulfide (m-CN/BP/MoS2) was firstly fabricated for the visible-light-driven hydrogen evolution reaction (HER) via water splitting. The photocatalytic activity of m-CN/BP/MoS2 photocatalyst was further improved by incorporating Ni and Co co-catalysts, denoted as m-CN/BP/MoS2-Y (Y: Ni, Co). The final quaternary nanocomposites were experimentally demonstrated in the form of mixed heterojunctions (type-I, type-II, and Schottky junctions) to manipulate the photogenerated carriers with the aim of reducing their recombination rate and increasing the light-harvesting ability of the pristine components. To find the best combination of different semiconductors in the heterojunction to ensure the highest photocatalytic HER activity, the loading ratio of each component was optimized one-by-one by considering the rate of HER under the same conditions. The photocatalytic HER activity of m-CN/BP/MoS2-Ni (5 wt%) and m-CN/BP/MoS2-Co (0.5 wt%) photocatalysts reached up to 21.668 mmol g−1 and 29.179 mmol g−1 for 8 h in the presence of triethanolamine electron donor under visible light irradiation, which were about 11 and 15 times higher than that of m-CN/BP binary heterojunctions, 4 and 5 times higher than that of m-CN/BP/MoS2 ternary heterojunctions, respectively. Ni or Co co-catalysts enhanced charge separation and thus increasing the rate of H2 evolution owing to their suitable d-band levels. This present study supplies a strategy to design efficient photocatalysts for solar fuel production without using non-noble metal cocatalysts.

Distinct selectivity control in solar-driven bio-based α-hydroxyl acid conversion: a comparison of Pt nanoparticles and atomically dispersed Pt on CdS.

Solar-driven photocatalytic lignocellulose conversion is a promising strategy for the sustainable production of high-value chemicals, but selectivity control remains a challenging goal in this field. Here, we report efficient and selective conversion of lignocellulose-derived α-hydroxyl acids to tartaric acid derivatives, α-keto acids, and H2 using Pt-modified CdS catalysts. Pt nanoparticles on CdS selectively produce tartaric acid derivatives via C-C coupling, while atomically dispersed Pt on CdS switches product selectivity to oxidation reaction to produce α-keto acids. The atomically dispersed Pt species stabilized by Pt-S bonds promote the activation of hydroxyl group and thus switch product selectivity from tartaric acid derivatives to α-keto acids. A broad range of lignocellulose-derived α-hydroxyl acids was applied for preparing the corresponding tartaric acid derivatives and α-keto acids over the two Pt-modified CdS catalysts. This work highlights the unique performance of metal sulfides in coupling reactions and demonstrates a strategy for rationally tuning product selectivity by engineering the interaction between metal sulfide and cocatalyst.

Distinct Selectivity Control in Solar‐Driven Bio‐Based α‐Hydroxyl Acid Conversion: A Comparison of Pt Nanoparticles and Atomically Dispersed Pt on CdS

AbstractSolar‐driven photocatalytic lignocellulose conversion is a promising strategy for the sustainable production of high‐value chemicals, but selectivity control remains a challenging goal in this field. Here, we report efficient and selective conversion of lignocellulose‐derived α‐hydroxyl acids to tartaric acid derivatives, α‐keto acids, and H2 using Pt‐modified CdS catalysts. Pt nanoparticles on CdS selectively produce tartaric acid derivatives via C−C coupling, while atomically dispersed Pt on CdS switches product selectivity to the oxidation reaction to produce α‐keto acids. The atomically dispersed Pt species stabilized by Pt−S bonds promote the activation of the hydroxyl group and thus switch product selectivity from tartaric acid derivatives to α‐keto acids. A broad range of lignocellulose‐derived α‐hydroxyl acids was applied for preparing the corresponding tartaric acid derivatives and α‐keto acids over the two Pt‐modified CdS catalysts. This work highlights the unique performance of metal sulfides in coupling reactions and demonstrates a strategy for rationally tuning product selectivity by engineering the interaction between metal sulfide and cocatalyst.

Enhanced photocatalytic hydrogen production utilizing few-layered 1T-WS2/g-C3N4 heterostructures prepared with one-step calcination route

Two-dimensional sulfide is considered as one of the best alternative for noble metal cocatalyst, whereas few-layered 1T WS2 structure is very helpful to promote the photocatalytical activity for hydrogen generation. Herein, few-layered 1T-WS2/g-C3N4 composites have been prepared via a facile one-step calcination route and used as a noble metal-free catalyst for H2 evolution. The results showed that the optimized 1T-WS2/g-C3N4 has a H2 evolution rate of 10.08 mmol∙g−1 h−1, which is 180 and 2.44 times larger than that of pure pristine g-C3N4 and g-C3N4 (Pt), respectively. The enhanced photocatalytic activity can be explained as the optimized 1T-WS2/g-C3N4 sample has an increased light absorption (from visible to infrared region), better electrical conductivity and high density of active sites. The studies will be helpful for constructing high efficient heterostructured catalysts by loading 1T phase metal dichalcogenides 2D of material onto a two-dimensional material surface.

(Digital Presentation) 2D Molybdenum Disulfide Nanosheets As Cocatalyst and Passivation Layer over CuInS2 Based Photocathode for Solar Hydrogen Evolution

An excellent strategy to improve photoelectrochemical (PEC) water splitting is to develop cost-effective co-catalysts that do not use noble metals such as Platinum (Pt), Iridium (Ir), Ruthenium (Ru). Transition metal cocatalysts have shown excellent catalytic property towards hydrogen evolution (HER) and oxygen evolution reaction (OER). The surface active sites and lower free energy of H* adsorption (GH adsorption) on the surface are the factors ameliorating and boosting their catalytic activity. Molybdenum Disulfide (MoS2), one the transition metal dichalcogenide with 2D-sheet like structure with high surface area, active sites, and excellent property to catalyze HER comparable to Pt. The property of higher stability towards the photocorrosion as compared to other cocatalysts provides MoS2 with an additional feature of passivation layer. The sheet-like structure also enhances the light absorption minimizing the effect of parasitic light absorption.Copper based oxides and chalcogenides are well known p-type semiconductors being investigated for photocathode materials to be used in unassisted PEC water splitting cell. CuInS2, a ternary copper chalcogenide material with tunable bandgap (Eg = 1.5-1.8 eV), high absorption coefficient (> 104), suitable band positions for hydrogen evolution reaction. Despite all the necessary features and properties, it suffers with the problem of high rate of recombination between photogenerated charge carriers, lower diffusional lengths and poor photostability. Several approaches have been developed to improve the PEC performance of CuInS2 that include decoration of metal NPs, heterojunction fabrication, deposition of electron (ETLs) and hole transporting layers (HTLs). CdS forms a proper heterojunction with CuInS2 owing to its conduction (CB) and valence (VB) offsets.The integration of CuInS2 with CdS could form a facile heterojunction for the effective charge separation and reduce the rate of recombination and decoration of MoS2 over the CuInS2/CdS can be beneficial in terms of improved reaction kinetics at the surface and photostability by avoiding direct contact of CuInS2 and CdS with electrolyte. A CuInS2 nanosheet array-based photocathode that is modified with CdS and the co-catalyst MoS2. This green approach enhances water splitting under solar irradiation. By introducing CdS and MoS2, we significantly improved the visible light absorption of the modified hybrid photocathode (CIS/CdS/MoS2). Photoluminescence, impedance spectroscopy, and Mott–Schottky analysis confirmed that excited electron-hole pairs were better separated, the resistance of charge transfer was minimized, and the excited-state charge carrier concentration increased, leading to increased photocurrent.Typical results demonstrated that CIS/CdS/MoS2 photocathode delivered higher photocurrent (-1.75 mA/cm2 at 0 VRHE) and HC-STH conversion efficiency (0.42% at 0.49 VRHE) than those of CIS and CIS/CdS photoelectrodes. We attribute this improved PEC performance to the synergetic impact of CdS in charge generation and transfer and MoS2 as a cocatalyst with active surface sites for proton reduction. The hydrogen evolution experiment showed CIS/CdS/MoS2 (56.9 μmol/h) showed high activity and rate of hydrogen evolution compared to CIS (22.6 μmol/h). This study not only demonstrates the promising nature of CuInS2-based light absorber photocathodes for solar energy utilization but also recommends the use of MoS2 as a cocatalyst for the proton reduction reactions for widespread applications in solar-to-hydrogen conversion. Reference (1) Kumar, M.; Meena, B.; Subramanyam, P.; Ummethala, G.; Malladi, S. R. K.; Dutta-Gupta, S.; Subrahmanyam, C. CuInS 2 Nanosheet Arrays with a MoS 2 Heterojunction as a Photocathode for PEC Water Splitting. Energy & Fuels 2023, 37 (3), 2340–2349. https://doi.org/10.1021/acs.energyfuels.2c03502. Figure 1

Self-optimized H-adsorption affinity of CuRu alloy cocatalysts towards efficient photocatalytic H2 evolution

In addition to the electron transfer, the appropriate H-adsorption affinity of active centers on the metal cocatalyst surface is quite important for high hydrogen-production activity of cocatalyst-modified photocatalysts. The typical Cu and Ru metal cocatalysts clearly exhibit a weak Cu–H bond and a strong Ru–H bond, respectively, resulting in limited activity for photocatalytic H2 evolution. In this work, an ingenious strategy of self-optimized H-adsorption affinity in CuRu alloy cocatalyst is developed to simultaneously reinforce the Cu–H bond and weaken the Ru–H bond by the intrinsic electron transfer from Cu to Ru atom. The CuRu alloy nanoparticles (2–3 nm) were deposited on the TiO2 surface to prepare CuRu/TiO2 through a one-step photoreduction method. Photocatalytic tests exhibited that the highest H2-production rate of CuRu/TiO2 photocatalyst reached up to 5.316 mmol h–1 g–1, which was 24.80, 1.86, and 2.60 times higher than that of the TiO2, Cu/TiO2, and Ru/TiO2, respectively. Based on the characterization results and theoretical calculations, the CuRu alloy cocatalyst exhibits excellent self-optimized H-adsorption affinity via the spontaneous electron transfer from Cu to Ru atom, which can greatly accelerate the photocatalytic H2-production rate of TiO2. This work provides a feasible idea for the self-optimized H-adsorption affinity of metal active sites in the photocatalytic H2-generation field.

Sugar-Assisted Kinetic Resolutions in Metal/Chiral Amine Co-Catalyzed α-Allylations and [4+2] Cycloadditions: Highly Enantioselective Synthesis of Sugar and Chromane Derivatives.

Functionalized triose-, furanose and chromane-derivatives were synthesized by the titled reactions. The sugar-assisted kinetic resolution/C-C bond-forming cascade processes generate a functionalized sugar derivative with a quaternary stereocenter in a highly enantioselective fashion (up to >99 % ee) by using a simple combination of metal and chiral amine co-catalysts. Notably, the interplay between the chiral sugar substrate and the chiral amino acid derivative allowed for the construction of a functionalized sugar product with high enantioselectivity (up to 99 %) also when using a combination of racemic amine catalyst (0 % ee) and metal catalyst.

Non-noble metal based nickel phosphate decorated CdS nanorods for persistent and efficient solar-to-hydrogen conversion

Solar-to-hydrogen conversion is a potential technology to help end our dependency on fossil fuels. The electron cloud structure of metal sulfide is more suitable than oxide for the preparation of photocatalytic materials. However, their low production rate has always been a limiting factor. Precious metal cocatalysts, such as Pt, Pd, Au, and Ru, are often introduced to tackle this problem. But in fact, their high price and scarcity limit their large-scale application in photocatalysis. At the same time, photooxidation corrosion has always been a problem in the application of metal sulfide. In the present study, we loaded cadmium sulfide (CdS) nanorods with noble metal-free nickel-based cocatalyst at room temperature. The reaction conditions were mild, making the process facile and easy to control. The nickel-based cocatalyst successfully prevented the oxidative photocorrosion of CdS, making the composite material stable for an extended time. The suggested non-noble metal-based cocatalyst had better performance than the traditional Pt cocatalyst. The hydrogen production rate was 58 mmol/g/h at the reaction time of 5 h, and the cumulative hydrogen production was kept up to 35 h with the same evolution rate. Overall, the results were striking to serve a new idea for efficient and persistent photocatalytic hydrogen generation using a non-noble metal-based photocatalyst.

Effects of potassium ions and platinum cocatalysts on the photocatalytic performance of Poly(Heptazine Imides)

In the synthesis of highly crystalline carbon nitride, alkali metal halides are used as high-temperature solvents and structural guiding agents, but the effect of alkali metal ions on the catalytic activity of materials is still unclear. In addition, the shape and size of the cocatalyst also significantly affect the catalytic activity of the material. Therefore, we have carried out the density functional theory calculations to reveal the differences in the structure, electronic, and optical properties, as well as the photocatalytic hydrogen evolution performance of one kind of crystalline carbon nitride called potassium poly(heptazine imide) (K-PHI) and its proton-exchanged counterpart (H-PHI) loaded with different sizes of platinum cocatalysts. The results show that potassium ions have the effect of aggregation electrons in K-PHI, and potassium ions have short-range induced dipole effect on nearby Pt atoms, resulting in slightly better photocatalytic hydrogen evolution activity at these reaction sites. Additionally, Pt cocatalyst with larger load size has better photocatalytic hydrogen evolution activity than small size. This work provides a theoretical basis for the rational design of high-performance metal cocatalysts and exploration of the functionality of alkali metal ions in carbon nitrides.

CoO/g-C3N4 p-n heterojunction catalyst in-situ loading CoP for enhanced photocatalytic H2 evolution

A prospective and pollution-free approach for producing hydrogen is photocatalytic water-splitting. Designing and developing a catalyst that can separate the photogenerated carriers and offer enough H+ reduction active sites are of paramount importance in boosting the efficiency of photocatalytic H2 evolution. Herein, the cocatalyst CoP were loaded on CoO/g-C3N4 p-n heterojunction (CoP/CoO/CN, referring g-C3N4 to as CN) by an in-situ phosphating method, and its H2 evolution activity was measured by simulating sunlight irradiation without adding any noble metal cocatalyst. The CoP/CoO/CN photocatalyst exhibited a better H2 evolution activity (4036.97 μmol·g−1·h−1) than Pt/CN. The mechanism study demonstrated that the excellent activity is resulted from the formed internal electric field in p-n heterojunction, and the enough active reduction sites from cocatalyst CoP. This work provides a rational design for in-situ loading cocatalysts on heterojunction and is helpful for developing efficient photocatalysts using the abundant low-cost elements.

Highly selective photocatalytic CO 2 reduction to ethylene in pure water by Nb 2O 5 nanoparticles with enriched surface –OH groups under simulated solar illumination

Photocatalytic CO₂ reduction to valuable chemical compounds could be a promising approach for carbon neutral practice. In this work, a simple and robust thermal decomposition process was developed with ammonium carbonate as both the precipitation agent and sacrificial template to produce fine Nb₂O₅ nanoparticles with a rich existence of surface -OH groups. It was found by Density Functional Theory (DFT) calculations and experiments that the rich existence of surface -OH groups enhanced the adsorption of both reactants (CO₂ and H₂O molecules) for the photocatalytic CO₂ reduction on these fine Nb₂O₅ nanoparticles, and a highly selective conversion of CO₂ to a high value chemical compound of ethylene (~ 68 mmol·g^-1·h^-1 with ~ 100% product selectivity) was achieved under simulated solar illumination without the usage of any sacrificial agents or noble metal cocatalysts. This synthesis process may also be readily applied as a surface engineering method to enrich the existence of surface -OH groups on various metal oxide-based photocatalysts for a broad range of technical applications.

4-Methyl-5-vinyl thiazole modified Ni-MOF/g-C3N4/CdS composites for efficient photocatalytic hydrogen evolution without precious metal cocatalysts

The construction of heterojunction systems is an effective way to efficiently generate hydrogen by water photolysis. In this work, Ni-MOF (trimesic acid, (BTC)) and g-C3N4 (denoted as CN) were combined, and then Ni-MOF/CN was modified by 4-Methyl-5-vinyl thiazole (denoted as MVTh). Finally, CdS was loaded on the surface of Ni-MOF/CN/MVTh to prepare the photocatalyst Ni-MOF/g-C3N4/MVTh/CdS (denoted as Ni/CN/M/Cd) with a triangular closed-loop path heterojunction for the first time. As a photocatalyst without precious metal cocatalysts, Ni/CN/M/Cd displayed high H2 evolution (17.844 mmol·g−1·h−1) under an optimum CdS loading of 40 wt%. The H2 evolution rate was approximately 79 times that of Ni-MOF/CN and exceeded those of almost all catalysts based on MOF/CN in the literature. The triangular closed-loop heterojunction formed between Ni-MOF, g-C3N4, and CdS could realize the directional migration of photocarriers and significantly diminished the transfer resistance of carriers. The Ni2+ in Ni-MOF provided many cocatalytic sites for H2 evolution via g-C3N4 and CdS. Furthermore, charge carrier separation in Ni-MOF/CN/CdS improved after the innovative addition of MVTh. This study provides a reference for the construction of a closed-loop heterojunction system without precious metal cocatalysts.

Performance of recent transition metal cocatalysts under hydrogen evolution reaction

In case clean and renewable energy on earth is urgently needed, converting solar energy into hydrogen is applied. Due to its high efficiency and low cost, photoelectrochemical water splitting (PEC) has become a popular strategy. To achieve this, non-noble metal electrocatalysts as cocatalysts are used to enhance the performance of PEC water splitting. In this review, the recent procedure of the synthesis, performance measurements, and the result of MoSx, TiO2/NiOx, Pt/TiO2/InAs NWs, and CoS are introduced. These materials show a fit onset potential, good current density, and small charge transfer resistance for hydrogen evolution reaction (HER). Compared with TiO2/NiOx, Pt/TiO2/InAs NWs, and CoS, MoSx is the only stable under acidic conditions. Some suggestions for future research on transition metal-based electrocatalysts are also provided.

A Highly Efficient Composite Catalyst (Au/Ta3N5)/CdS for Photocatalytic Hydrogen Production

As non-noble metal co-catalysts, Nitrides have received extensive attention for their high efficiency and low cost in photocatalytic hydrogen production. In this study, we develop a novel composite co-catalyst of Au/Ta3N5 that significantly enhanced the photocatalytic hydrogen production activity of CdS. The activity of photocatalyst (Au/Ta3N5)/CdS is 7.3 times of bare CdS and 2.2 times of Ta3N5/CdS. The proper capacitance and enhanced activity of Ta3N5 demonstrates the capacitance catalysis effect of Ta3N5, which improves the charges separation and storing of the photoexcited electrons from CdS. Au acts as an active site for proton reduction to further improve the activity.

Beyond Reduction Cocatalysts: Critical Role of Metal Cocatalysts in Photocatalytic Oxidation of Methane with Water.

Environmentally sustainable and selective conversion of methane to valuable chemicals under ambient conditions is pivotal for the development of next-generation photocatalytic technology. However, due to the lack of microscopic knowledge about non-thermal methane conversion, controlling and modulating photocatalytic oxidation processes driven by photogenerated holes remain a challenge. Here, we report novel function of metal cocatalysts to accept photogenerated holes and dominate selectivity of methane oxidation, which is clearly beyond the conventional concept in photocatalysis that the metal cocatalysts loaded on the surfaces of semiconductor photocatalysts mostly capture photogenerated electrons and dominate reduction reactions exclusively. The novel photocatalytic role of metal cocatalysts was verified by operando molecular spectroscopy combined with real-time mass spectrometry for metal-loaded Ga2O3 model photocatalysts under methane and water vapor at ambient temperature and pressure.Our concept of metal cocatalysts that work as active sites for both photocatalytic oxidation and reduction provides a new understanding of photocatalysis and a solid basis for controlling non-thermal redox reactions by metal-cocatalyst engineering.

Beyond Reduction Cocatalysts: Critical Role of Metal Cocatalysts in Photocatalytic Oxidation of Methane with Water**

AbstractEnvironmentally sustainable and selective conversion of methane to valuable chemicals under ambient conditions is pivotal for the development of next‐generation photocatalytic technology. However, due to the lack of microscopic knowledge about non‐thermal methane conversion, controlling and modulating photocatalytic oxidation processes driven by photogenerated holes remain a challenge. Here, we report novel function of metal cocatalysts to accept photogenerated holes and dominate selectivity of methane oxidation, which is clearly beyond the conventional concept in photocatalysis that the metal cocatalysts loaded on the surfaces of semiconductor photocatalysts mostly capture photogenerated electrons and dominate reduction reactions exclusively. The novel photocatalytic role of metal cocatalysts was verified by operando molecular spectroscopy combined with real‐time mass spectrometry for metal‐loaded Ga2O3 model photocatalysts under methane and water vapor at ambient temperature and pressure. Our concept of metal cocatalysts that work as active sites for both photocatalytic oxidation and reduction provides a new understanding of photocatalysis and a solid basis for controlling non‐thermal redox reactions by metal‐cocatalyst engineering.