The Rational Design of a Single-Component Photocatalyst for Gas-Phase CO2 Reduction Using Both UV and Visible Light

Single-Atom Titanium on Mesoporous Nitrogen, Oxygen-Doped Carbon for Efficient Photo-thermal Catalytic CO2 Cycloaddition by a Radical Mechanism

Developing efficient and earth-abundant catalysts for CO2 fixation to high value-added chemicals is meaningful but challenging. Styrene carbonate has great market value, but the cycloaddition of CO2 to styrene oxide is difficult due to the high steric hindrance and weak electron-withdrawing ability of the phenyl group. To utilize clean energy (such as optical energy) directly and effectively for CO2 value-added process, we introduce earth-abundant Ti single-atom into the mesoporous nitrogen, oxygen-doped carbon nanosheets (Ti-CNO) by a two-step method. The Ti-CNO exhibits excellent photothermal catalytic activities and stability for cycloaddition of CO2 and styrene oxide to styrene carbonate. Under light irradiation and ambient pressure, an optimal Ti-CNO produces styrene carbonate with a yield of 98.3 %, much higher than CN (27.1 %). In addition, it shows remarkable stability during 10 consecutive cycles. Its enhanced catalytic performance stems from the enhanced photothermal effect and improved Lewis acidic/basic sites exposed by the abundant mesopores. The experiments and theoretical simulations demonstrate the styrene oxide⋅+ and CO2⋅- radicals generated at the Lewis acidic (Tiδ+) and basic sites of Ti-CNO under light irradiation, respectively. This work furnishes a strategy for synthesizing advanced single-atom catalysts for photo-thermal synergistic CO2 fixation to high value products via a cycloaddition pathway.

Rapid Surface Reconstruction of In2S3 Photoanode via Flame Treatment for Enhanced Photoelectrochemical Performance

Surface reconstruction, reorganizing the surface atoms or structure, is a promising strategy to manipulate materials' electrical, electrochemical, and surface catalytic properties. Herein, a rapid surface reconstruction of indium sulfide (In2S3) is demonstrated via a high-temperature flame treatment to improve its charge collection properties. The flame process selectively transforms the In2S3 surface into a diffusionless In2O3 layer with high crystallinity. Additionally, it controllably generates bulk sulfur vacancies within a few seconds, leading to surface-reconstructed In2S3 (sr-In2S3). When using those sr-In2S3 as photoanode for photoelectrochemical water splitting devices, these dual functions of surface In2O3/bulk In2S3 reduce the charge recombination in the surface and bulk region, thus improving photocurrent density and stability. With optimized surface reconstruction, the sr-In2S3 photoanode demonstrates a significant photocurrent density of 8.5 mA cm-2 at 1.23 V versus a reversible hydrogen electrode (RHE), marking a 2.5-fold increase compared to pristine In2S3 (3.5 mA cm-2). More importantly, the sr-In2S3 photoanode exhibits an impressive photocurrent density of 7.3 mA cm-2 at 0.6 V versus RHE for iodide oxidation reaction. A practical and scalable surface reconstruction is also showcased via flame treatment. This work provides new insights for surface reconstruction engineering in sulfide-based semiconductors, making a breakthrough in developing efficient solar-fuel energy devices.

Oxygen-Vacancy-Mediated Large Binding Energy Exciton Dissociation in Nb3O7(OH) Nanorods with High Electron Mobility for CO2 Photoreduction

Despite the excellent performance of Nb3O7(OH) in dye-sensitized solar cells and catalysis, its charge separation, transport, and structural properties remain poorly understood. Herein, the Nb3O7(OH) nanorods were prepared, and their structural characteristics, optoelectronic properties, and carrier mobility were also analyzed and investigated through a series of complex characterizations. Theoretical prediction suggested that the exciton binding energy of Nb3O7(OH) could be as high as 100.49 meV. The temperature-dependent photoluminescence (PL) of Nb3O7(OH) nanorods revealed two activation energies, and a higher proportion of long-lived components observed in the photoluminescence decay indicated effective electron trapping. That is, two energy states were present, hindering photogenerated charge recombination and promoting photocatalytic action. Current-voltage characteristics of the Nb3O7(OH) nanorod film were analyzed, revealing an ultrahigh carrier mobility of ∼310 cm2/V·s, ensuring fast and efficient electron transfer. Furthermore, Nb3O7(OH) nanorods were employed to reduce CO2, resulting in the effective production of CO and CH4. Overall, considering the presence of hydroxyl pairs on the surface of Nb3O7(OH), which facilitate the formation of the frustrated Lewis acid-base pairs and the activation of CO2, together with its effective electron trapping and charge transport, give Nb3O7(OH) nanorods a promising potential for CO2 reduction.

High-Entropy Photothermal Materials

High-entropy (HE) materials, celebrated for their extraordinary chemical and physical properties, have garnered increasing attention for their broad applications across diverse disciplines. The expansive compositional range of these materials allows for nuanced tuning of their properties and innovative structural designs. Recent advances have been centered on their versatile photothermal conversion capabilities, effective across the full solar spectrum (300-2500 nm). The HE effect, coupled with hysteresis diffusion, imparts these materials with desirable thermal and chemical stability. These attributes position HE materials as a revolutionary alternative to traditional photothermal materials, signifying a transformative shift in photothermal technology. This review delivers a comprehensive summary of the current state of knowledge regarding HE photothermal materials, emphasizing the intricate relationship between their compositions, structures, light-absorbing mechanisms, and optical properties. Furthermore, the review outlines the notable advances in HE photothermal materials, emphasizing their contributions to areas, such as solar water evaporation, personal thermal management, solar thermoelectric generation, catalysis, and biomedical applications. The review culminates in presenting a roadmap that outlines prospective directions for future research in this burgeoning field, and also outlines fruitful ways to develop advanced HE photothermal materials and to expand their promising applications.

Solar-Driven Continuous CO2 Reduction to CO and CH4 using Heterogeneous Photothermal Catalysts: Recent Progress and Remaining Challenges

The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.

Towards maximizing the In2O3/m-ZrO2 interfaces for CO2-to-methanol hydrogenation

Through chelating-assisted impregnation with diethylenetriamine-pentaacetic acid (DTPA), we developed an efficient and durable CO2 hydrogenation catalyst, In15/m-ZrO2-DTPA, featuring improved In2O3 reducibility and interfacial Zr-O-In structures. Benefiting from its distinct CO2 activation and hydrogenation ability, In15/m-ZrO2-DTPA exhibited remarkable CO2-to-methanol catalytic activity, achieving up to 91% selectivity at 260 °C and 5.0 MPa, with consistent conversion maintained over 400 hours.

Native frustrated Lewis pairs on core-shell In@InOxHy enhances CO2-to-formate conversion

Strategies to efficiently activate CO2 by strongly inhibiting the competitive hydrogen evolution reaction process are highly desired for practical applications of the electrochemical CO2 reduction technique. Here, we assembled a core-shell In@InOxHy architecture on carbon black by one-step reduction of NaBH4 as a CO2-to-formate catalyst with high selectivity. The stable CO2-to-formate reaction originates from the creation of steritic frustrated Lewis pairs (FLPs) on the InOxHy shell with In-OVs (OVs, oxygen vacancies) Lewis acid, and In-OH Lewis base. During CO2 reduction, the electrochemically stable FLPs are capable of first capturing and stabilizing protons to protonate FLPs to In-H Lewis acid and In-OH2 Lewis base due to its strong steric electrostatic field; then, CO2 is captured and activated by the protonated FLPs to selectively produce formate. Our results demonstrated that FLPs can be created on the surface of oxyphilic single-metal catalysts efficient in accelerating CO2 reduction with high selectivity.

Subsurface oxygen defects electronically interacting with active sites on In2O3 for enhanced photothermocatalytic CO2 reduction

Oxygen defects play an important role in many catalytic reactions. Increasing surface oxygen defects can be done through reduction treatment. However, excessive reduction blocks electron channels and deactivates the catalyst surface due to electron-trapped effects by subsurface oxygen defects. How to effectively extract electrons from subsurface oxygen defects which cannot directly interact with reactants is challenging and remains elusive. Here, we report a metallic In-embedded In₂O₃ nanoflake catalyst over which the turnover frequency of CO₂ reduction into CO increases by a factor of 866 (7615 h⁻¹) and 376 (2990 h⁻¹) at the same light intensity and reaction temperature, respectively, compared to In₂O₃. Under electron-delocalization effect of O-In-(O)V_o-In-In structural units at the interface, the electrons in the subsurface oxygen defects are extracted and gather at surface active sites. This improves the electronic coupling with CO₂ and stabilizes intermediate. The study opens up new insights for exquisite electronic manipulation of oxygen defects.

How to effectively extract electrons from subsurface oxygen defects is challenging in heterogeneous catalysis. Here the authors demonstrate that Metallic In-embedded In2O3 nanoflake catalyst promotes the delocalization of electrons among subsurface oxygen defects, obviously increasing electron density of surface active sites.

Photodriven CO2 Hydrogenation into Diverse Products: Recent Progress and Perspective

Converting CO2 into value-added chemicals through hydrogenation can optimize the energy structure dominated by fossil energy, effectively alleviate environmental problems, and achieve full utilization of carbon resources. However, the traditional CO2 hydrogenation reactions need to be carried out under high temperature and pressure, causing inevitable secondary pollution to the environment. A fundamental way to solve these problems is to use clean solar energy to convert CO2 into value-added chemicals and to establish an artificial carbon cycle process. In this Perspective, we highlight recent advances in photodriven CO2 conversion, including the reverse water-gas-shift reaction, methanation reaction, methanol synthesis reaction, and C2+ hydrocarbon synthesis reaction. Finally, we also discuss the challenges and future investigation opportunities for modulating the selective conversion of CO2. This Perspective offers guidance for the design of photodriven CO2 conversion or even the entire C1 catalyst chemistry for tuning product selectivity and activity.

Synthesis of High Surface Area-Group 13-Metal Oxides via Atomic Layer Deposition on Mesoporous Silica

The atomic layer deposition of gallium and indium oxide was investigated on mesoporous silica powder and compared to the related aluminum oxide process. The respective oxide (GaO_x, InO_x) was deposited using sequential dosing of trimethylgallium or trimethylindium and water at 150 °C. In-situ thermogravimetry provided direct insight into the growth rates and deposition behavior. The highly amorphous and well-dispersed nature of the oxides was shown by XRD and STEM EDX-mappings. N₂ sorption analysis revealed that both ALD processes resulted in high specific surface areas while maintaining the pore structure. The stoichiometry of GaO_x and InO_x was suggested by thermogravimetry and confirmed by XPS. FTIR and solid-state NMR were conducted to investigate the ligand deposition behavior and thermogravimetric data helped estimate the layer thicknesses. Finally, this study provides a deeper understanding of ALD on powder substrates and enables the precise synthesis of high surface area metal oxides for catalytic applications.

Accelerating photo-thermal CO2 reduction to CO, CH4 or methanol over metal/oxide semiconductor catalysts

Photo-thermal reduction of atmospheric carbon dioxide into methane, methanol, and carbon monoxide under mild conditions over suitable (photo)catalysts is a feasible pathway for the production of fuels and platform chemicals with minimal involvement of fossil fuels. In this perspective, we showcase transition metal nanoparticles (Ni, Cu, and Ru) dispersed over oxide semiconductors and their ability to act as photo catalysts in reverse water gas shift reaction (RWGS), methane dry reforming, methanol synthesis, and Sabatier reactions. By using a combination of light and thermal energy for activation, reactions can be sustained at much lower temperatures compared to thermally driven reactions and light can be used to leverage reaction selectivity between methanol, methane, and CO. In addition to influencing the reaction mechanism and decreasing the apparent activation energies, accelerating reaction rates and boosting selectivity beyond thermodynamic limitations is possible. We also provide future directions for research to advance the current state of the art in photo-thermal CO₂ conversion.

Optical Detection of Copper Ions via Structural Dissociation of Plasmonic Sugar Nanoprobes

Heavy metal ions are known to cause environmental pollution and several human diseases because of their inherent toxicity. Among them, Cu²⁺ is an essential element for the human body, but its continuous exposure and accumulation may cause adverse effects. Thus, copper ion levels in aquatic environments are strictly regulated by international standards. Herein, we demonstrate a simple optical method for detecting Cu²⁺ using plasmonic sugar nanoprobes (PSNs) composed of gold nanoparticles and polysaccharides. Gold precursors were reduced to nanoparticles and spontaneously embedded in the sugar-based polymeric network with the sulfated residues of carrageenan during the polymerization procedure. Owing to the abundant functional residues of PSNs and their affinity toward Cu²⁺, we observed the Cu²⁺-mediated preferential dissociation of the PSNs, resulting in absorbance spectral shifts and scattering shifts of the PSNs. Based on these plasmon band shifts, Cu²⁺ below the EPA regulation level of 20 μM can be easily detected by the optimized experimental condition. Additionally, the reaction mechanism between the PSNs and Cu²⁺ was elucidated by indepth spectroscopic analyses, which revealed that the increased binding of Cu²⁺ to the sulfate groups in the PSNs induces the eventual decomposition of the PSNs.

Boosting Electrochemical Activity of Porous Transparent Conductive Oxides Electrodes Prepared by Sequential Infiltration Synthesis

Sequential infiltration synthesis (SIS) is an emerging technique for producing inorganic-organic hybrid materials and templated inorganic nanomaterials. The application space for SIS is expanding rapidly in areas such as lithography, filtration, photovoltaics, antireflection, and triboelectricity, but not in the field of electrochemistry. This study performs SIS for the fabrication of porous, transparent, and electrically conductive films of indium zinc oxide (IZO) to evaluate their potential as an electrode for electrochemistry. The electrochemical activity of IZO-coated electrodes is evaluated when their surfaces are modified with ferrocenecarboxylic acid (FcCOOH), a model redox molecule. Results show a 25-fold enhancement in peak current densities mediated by an Fc/Fc⁺ redox couple for an IZO-coated electrode in comparison with bare electrodes; this is afforded by the porous morphology of the IZO film and the enhanced binding efficiency of FcCOOH on the IZO film. The results confirm the potential of SIS for the preparation of porous transparent conducting oxide electrodes, which will enable the application of SIS-derived materials in various electrochemical fields.

Introducing Graphene–Indium Oxide Electrochemical Sensor for Detecting Ethanol in Aqueous Samples with CCD-RSM Optimization

There is significant demand for portable sensors that can deliver selective and sensitive measurement of ethanol on-site. Such sensors have application across many industries, including clinical and forensic work as well as agricultural and environmental analysis. Here, we report a new graphene–indium oxide electrochemical sensor for the determination of ethanol in aqueous samples. Graphene layers were functionalised by anchoring In2O3 to its surface and the developed composite was used as a selective electrochemical sensor for sensing ethanol through cyclic voltammetry. The detection limit of the sensor was 0.068 mol/L and it showed a linear response to increasing ethanol in the environment up to 1.2 mol/L. The most significant parameters involved and their interactions in the response of the sensor and optimization procedures were studied using a four-factor central composite design (CCD) combined with response surface modelling (RSM). The sensor was applied in the detection of ethanol in authentic samples.

Turbulence Enhancement and Mixing Analysis for Multi-Inlet Vortex Photoreactor for CO2 Reduction

In this article, we describe a prototype photoreactor of which the geometrical configuration was obtained by Genetic Algorithms to maximize the residence time of the reactant gases. A gas reaction mixture of CO2:H2O (1:2 molar ratio) was studied from the fluid dynamic point of view. The two main features of this prototype reactor are the conical shape, which enhances the residence time as compared to a cylindrical shape reference reactor, and the inlet heights and position around the main chamber that enables turbulence and mass transfer control. Turbulence intensity, mixing capability, and residence time attributes for the optimized prototype reactor were calculated with Computational Fluid Dynamics (CFD) software and compared with those from a reference reactor. Turbulence intensity near the envisioned catalytic bed was one percentage point higher in the reference than in the optimized prototype reactor. Finally, the homogeneity of the mixture was guaranteed since both types of reactors had a turbulent regime, but for the prototype the CO2 mass fraction was found to be better distributed.

Nanostructured Photothermal Materials for Environmental and Catalytic Applications

Solar energy is a green and sustainable clean energy source. Its rational use can alleviate the energy crisis and environmental pollution. Directly converting solar energy into heat energy is the most efficient method among all solar conversion strategies. Recently, various environmental and energy applications based on nanostructured photothermal materials stimulated the re-examination of the interfacial solar energy conversion process. The design of photothermal nanomaterials is demonstrated to be critical to promote the solar-to-heat energy conversion and the following physical and chemical processes. This review introduces the latest photothermal nanomaterials and their nanostructure modulation strategies for environmental (seawater evaporation) and catalytic (C1 conversion) applications. We present the research progress of photothermal seawater evaporation based on two-dimensional and three-dimensional porous materials. Then, we describe the progress of photothermal catalysis based on layered double hydroxide derived nanostructures, hydroxylated indium oxide nanostructures, and metal plasmonic nanostructures. Finally, we present our insights concerning the future development of this field.

Construction of New Active Sites: Cu Substitution Enabled Surface Frustrated Lewis Pairs over Calcium Hydroxyapatite for CO2 Hydrogenation

Calcium hydroxyphosphate, Ca₁₀ (PO₄ )₆ (OH)₂ , is commonly known as hydroxyapatite (HAP). The acidic calcium and basic phosphate/hydroxide sites in HAP can be modified via isomorphous substitution of calcium and/or hydroxide ions to enable a cornucopia of catalyzed reactions. Herein, isomorphic substitution of Ca²⁺ ions by Cu²⁺ ions especially at very low levels of exchange created new analogs of molecular surface frustrated Lewis pairs (SFLPs) in Cu_x Ca_10-x (PO₄ )₆ (OH)₂ , thereby boosting its performance metrics in heterogeneous CO₂ photocatalytic hydrogenation. In situ Fourier transform infrared spectroscopy characterization and density functional theory calculations provided fundamental insights into the catalytically active SFLPs defined as proximal Lewis acidic Cu²⁺ and Lewis basic OH^- . The photocatalytic pathway proceeds through a formate reaction intermediate, which is generated by the reaction of CO₂ with heterolytically dissociated H₂ on the SFLPs. Given the wealth of information thus uncovered, it is highly likely that this work will spur the further development of similar classes of materials, leading to the advancement and, ultimately, large-scale application of photocatalytic CO₂ reduction technologies.

Conductive Polymer-Assisted Metal Oxide Hybrid Semiconductors for High-Performance Thin-Film Transistors

Metal oxide semiconductors doped with additional inorganic cations have insufficient electron mobility for next-generation electronic devices so strategies to realize the semiconductors exhibiting stability and high performance are required. To overcome the limitations of conventional inorganic cation doping to improve the electrical characteristics and stability of metal oxide semiconductors, we propose solution-processed high-performance metal oxide thin-film transistors (TFTs) by incorporating polyaniline (PANI), a conductive polymer, in a metal oxide matrix. The chemical interaction between the metal oxide and PANI demonstrated that the defect sites and crystallinity of the semiconductor layer are controllable. In addition, the change in oxygen-related chemical bonding of PANI-doped indium oxide (InO_x) TFTs induces superior electrical characteristics compared to pristine InO_x TFTs, even though trace amounts of PANI are doped in the semiconductor. In particular, the average field-effect mobility remarkably enhanced from 15.02 to 26.58 cm² V^-1 s^-1, the on/off current ratio improved from 10⁸ to 10⁹, and the threshold voltage became close to 0 V actually from -7.9 to -1.4 V.

Enhanced CO2 Photocatalysis by Indium Oxide Hydroxide Supported on TiN@TiO2 Nanotubes

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO₂ nanoparticulate intermediate layer and a In₂O_3-x(OH)_y nanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO₂ photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In₂O_3-x(OH)_y nanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO₂ nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In₂O_3-x(OH)_y nanoparticles and participate in the reactions occurring at the catalyst surface.

Photothermal catalysts for hydrogenation reactions

Hydrogenation reactions are an important process in today's chemical industry. Typically, hydrogenation reactions involve the removal of an unsaturated bond in olefins or other polyenes via thermal catalysis using hydrogen. As hydrogenation reactions are often carried out at temperatures up to several hundred degrees, they require significant energy input which typically comes from burning fossil fuels. In order to conserve fossil fuels and reduce CO₂ emissions, researchers are now developing photothermal catalysts for hydrogenation reactions, which harness concentrated sunlight to achieve the required reaction temperatures or introduce sunlight into thermal-driven reaction systems to reduce the reaction temperatures. Photothermal catalysts thus need to be able to efficiently absorb sunlight, whilst also being able to drive the desired hydrogenation reaction with high activity and selectivity. In this review, we summarize recent research aimed at the development of photothermal catalysts for CO₂/CO hydrogenation and alkene/alkyne/aromatic hydrogenation. Particular emphasis is placed on uncovering the reaction mechanisms at the molecular level, which in turn guides the rational design of photothermal catalysts with better performance.

Waveguide photoreactor enhances solar fuels photon utilization towards maximal optoelectronic - photocatalytic synergy

A conventional light management approach on a photo-catalyst is to concentrate photo-intensity to enhance the catalytic rate. We present a counter-intuitive approach where light intensity is distributed below the electronic photo-saturation limit under the principle of light maximization. By operating below the saturation point of the photo-intensity induced hydroxide growth under reactant gaseous H₂+CO₂ atmosphere, a coating of defect engineered In₂O_3-x(OH)_y nanorod Reverse Water Gas Shift solar-fuel catalyst on an optical waveguide outperforms a coated plane by a factor of 2.2. Further, light distribution along the length of the waveguide increases optical pathlengths of the weakly absorptive green and yellow wavelengths, which increases CO product rate by a factor of 8.1-8.7 in the visible. Synergistically pairing with thinly doped silicon on the waveguide enhances the CO production rate by 27% over the visible. In addition, the persistent photoconductivity behavior of the In₂O_3-x(OH)_y system enables CO production at a comparable rate for 2 h after turning off photo-illumination, enhancing yield with 44-62% over thermal only yield. The practical utility of persistent photocatalysis was demonstrated through outdoor solar concentrator tests, which after a day-and-night cycle showed CO yield increase of 19% over a day-light only period.

Influence of sulfur amount in Ni-incorporated ZnIn2(O,S)4 on phase formation and the visible light photocatalytic hydrogen evolution reaction

In the present work, we propose Ni-doped ZnIn₂(O,S)₄/In(OH)₃ composite particles for visible-light photocatalytic HER. By adjusting the sulfur concentration while keeping the amounts of zinc, indium and nickel constant during the hydrothermal process.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

Approaching full-range selectivity control in CO2 hydrogenation to methanol and carbon monoxide with catalyst composition regulation

P-Modified In₂O₃ with composition regulation for approaching full-range selectivity control in CO₂ hydrogenation to methanol and carbon monoxide.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels

In this work, we introduce HI-Light, a surface-engineered glass-waveguide-based “shell-and-tube” type photothermal reactor which is both scalable in diameter and length. We examine the effect of temperature, light irradiation, and residence time on its photo-thermocatalytic performance for CO₂ hydrogenation to form CO, with a cubic phase defect-laden indium oxide, In2O3-x(OH)y, catalyst. We demonstrate the light enhancement effect under a variety of reaction conditions. Notably, the light-on performance for the cubic nanocrystal photocatalyst exhibits a CO evolution rate at 15.40 mmol g_cat⁻¹ hr⁻¹ at 300°C and atmospheric pressure. This is 20 times higher conversion rate per unit catalyst mass per unit time beyond previously reported In2O3-x(OH)y catalyst in the cubic form under comparable operation conditions and more than 5 times higher than that of its rhombohedral polymorph. This result underscores that improvement in photo-thermocatalytic reactor design enables uniform light distribution and better reactant/catalyst mixing, thus significantly improving catalyst utilization.

•

- A glass-waveguide-based “shell-and-tube” type photothermal reactor was developed

•

The reactor exhibited a high photothermal catalytic performance for CO₂ reduction

•

- The modular reactor has potential for scale-up, both in diameter and length

•

The reactor design improves light distribution and reactant/catalyst mixing

Charge Redistribution Mechanisms in SnSe2 Surfaces Exposed to Oxidative and Humid Environments and Their Related Influence on Chemical Sensing

Tin diselenide (SnSe2) is a van der Waals semiconductor, which spontaneously forms a subnanometric SnO2 skin once exposed to air. Here, by means of surface-science spectroscopies and density functional theory, we have investigated the charge redistribution at the SnO2-SnSe2 heterojunction in both oxidative and humid environments. Explicitly, we find that the work function of the pristine SnSe2 surface increases by 0.23 and 0.40 eV upon exposure to O2 and air, respectively, with a charge transfer reaching 0.56 e-/SnO2 between the underlying SnSe2 and the SnO2 skin. Remarkably, both pristine SnSe2 and defective SnSe2 display chemical inertness toward water, in contrast to other metal chalcogenides. Conversely, the SnO2-SnSe2 interface formed upon surface oxidation is highly reactive toward water, with subsequent implications for SnSe2-based devices working in ambient humidity, including chemical sensors. Our findings also imply that recent reports on humidity sensing with SnSe2 should be reinterpreted, considering the pivotal role of the oxide skin in the interaction with water molecules.

Relating surface defect energetics with reactant gas adsorption during the photo-catalytic reduction of CO2 by partially hydrolyzed In2O3 nanorods

Photo-Induced Transient Current Spectroscopy (PICTS) is a versatile technique for measurements of defect state energies and densities in photo-active materials. It is suitable for investigating the surface-gas adsorbate behavior and the defect characteristics of defect laden In2O3-x(OH)y nanorods, having oxygen vacancies and hydroxide surface groups, under in situ reactor conditions of dark ambient temperature, dark 150 °C and photo-illuminated 150 °C, for the photo-assisted Reverse Water Gas Shift reaction. From glovebox-protected X-ray Photoelectron Spectroscopy and in situ PICTS measurements we determined that the reduction of CO2 is associated with heterolytic dissociation of H2 into In-H§- and HO-H§+ centres accompanied by an increase in average carrier trap energies; increased carbonate formation in a photo/thermal reactor state of H2 + CO2, and an average trap energy decrease of 0.11 eV from H2 to a CO2 + H2 mixture, which correlates with binding energy shifts of the OH shoulder of the O1s spectra. These results show the reactivity link between the various OH groups, oxygen vacancies and trap energies of In2O3-x(OH)y in the reactant gas atmosphere components.

Hybrid Photo- and Thermal Catalyst System for Continuous CO2 Reduction

Heterogeneous thermal catalytic processes are vital for industrial production of fuels, fertilizers, and other chemicals necessary for sustaining human life. However, these processes are highly energy-intensive, requiring a vast consumption of fossil fuels. An emerging class of heterogeneous catalysts that are thermally driven but also exhibit a photochemically enhanced rate can potentially reduce process energy intensity by partially substituting conventional heat (where fossil fuels are needed) with solar energy. Such catalyst systems have yet to be practically utilized. Here, we demonstrate a compact electrically heated photo- and thermal annular reactor module to reduce CO₂ to CO, via the reverse water gas shift reaction. A first-principles-based design approach was taken in developing a SiO₂ on an Al photo- and thermal catalyst system for the model photo- and thermal indium oxide hydroxide (In₂O_3-x(OH)_y) catalysts. A 5-fold light enhancement in the CO production rate and over 70 h of stable CO production were achieved. This represents the highest light enhancement effect reported for this model photocatalyst to date. The reactor presented herein allows continuous operation and a significant reduction of 31% in heater power consumption when provided with an additional 2 suns of irradiation, demonstrating the strong photo- and thermal-harvesting performances of the catalyst system developed in this work.

Organic-inorganic hybrids for CO2 sensing, separation and conversion

Motivated by the air pollution that skyrocketed in numerous regions around the world, great effort was placed on discovering new classes of materials that separate, sense or convert CO₂ in order to minimise impact on human health. However, separation, sensing and conversion are not only closely intertwined due to the ultimate goal of improving human well-being, but also because of similarities in material prerequisites -e.g. affinity to CO₂. Partly inspired by the unrivalled performance of complex natural materials, manifold inorganic-organic hybrids were developed. One of the most important characteristics of hybrids is their design flexibility, which results from the combination of individual constituents with specific functionality. In this review, we discuss commonly used organic, inorganic, and inherently hybrid building blocks for applications in separation, sensing and catalytic conversion and highlight benefits like durability, activity, low-cost and large scale fabrication. Moreover, we address obstacles and potential future developments of hybrid materials. This review should inspire young researchers in chemistry, physics and engineering to identify and overcome interdisciplinary research challenges by performing academic research but also - based on the ever-stricter emission regulations like carbon taxes - through exchanges between industry and science.

Photoinduced Defect Engineering: Enhanced Photothermal Catalytic Performance of 2D Black In2 O3- x Nanosheets with Bifunctional Oxygen Vacancies

Photothermal CO₂ reduction technology has attracted tremendous interest as a solution for the greenhouse effect and energy crisis, and thereby it plays a critical role in solving environmental problems and generating economic benefits. In₂ O_{3- x} has emerged as a potential photothermal catalyst for CO₂ conversion into CO via the light-driven reverse water gas shift reaction. However, it is still a challenge to modulate the structural and electronic characteristics of In₂ O₃ to enhance photothermocatalytic activity synergistically. In this work, a novel route to activate inert In(OH)₃ into 2D black In₂ O_{3- x} nanosheets via photoinduced defect engineering is proposed. Theoretical calculations and experimental results verify the existence of bifunctional oxygen vacancies in the 2D black In₂ O_{3- x} nanosheets host, which enhances light harvesting and chemical adsorption of CO₂ molecules dramatically, achieving 103.21 mmol g_cat ^-1 h^-1 with near-unity selectivity for CO generation and meanwhile excellent stability. This study reveals an exciting phenomenon that light is an ideal external stimulus on the layered In₂ O₃ system, and its electronic structure can be adjusted efficiently through photoinduced defect engineering; it can be anticipated that this synthesis strategy can be extended to wider application fields.

Synergistic Coupling of Photo and Thermal Conditions for Enhancing CO2 Reduction Rates in the Reverse Water Gas Shift Reaction

The photocatalytic activity of nanostructured In₂O_3-x(OH)_y for the reverse water gas shift (RWGS) reaction CO₂ + H₂ → CO + H₂O can be greatly enhanced by substitution of Bi(III) for In(III) in the lattice of Bi_zIn_2-zO_3-x(OH)_y. This behavior was hypothesized as the effect of the population and location of Bi(III) on the Lewis acidity and Lewis basicity of proximal hydroxide and coordinately unsaturated metal surface sites in Bi_zIn_2-zO_3-x(OH)_y acting synergistically as a frustrated Lewis acid-base pair reaction. Nonetheless, such photocatalytic activity is usually optimized in a specific batch reactor setup sequence, with H₂ as an initial gas input under photo and thermal conditions before introducing CO₂. Hence, the chemical interplay between environment parameters such as photoillumination, thermal input, and gas reactant components with the effects of Bi substitution is unclear. Reported herein, glovebox-protected X-ray photoelectron spectroscopy (XPS) interrogates this photochemical RWGS reaction transiting from vacuum state to similar conditions in a photocatalytic reactor, under dark and ambient temperatures, 150°C in dark and 150 °C under photoillumination. Binding energy shifts were used to correlate the material system's Lewis basicity response to these acidic probe gases. In-situ gas electronic sensitivity and in-situ UV-vis-derived band-gap trends confirm the trends shown in the XPS results, hence showing its equivalency with in situ methods. The enhanced photocatalytic reduction rate of CO₂ with H₂ with a low doped 0.05% a.t Bi system is thus associated with an increased gas sensitivity in H₂ + CO₂, a greater expansion in the OH shoulder than that of the undoped system under heat and light conditions, as well as a greater thermal stability of dissociated H adatoms. The photoinduced expansion of the OH shoulder and the increased positive binding energy shifts show the important role of photoillumination over that of thermal conditions. The poor catalytic performance of the high doped system can be attributed to a competing H₂ reduction of In³⁺. The results provide new insight into how pairing photo and thermal conditions with the methodical tuning of the Lewis acidity and Lewis basicity of surface frustrated Lewis acid-base pair sites by varying z amount in Bi_zIn_2-zO_3-x(OH)_y enables optimization of the rate of the photochemical RWGS.

Copper-Indium Binary Catalyst on a Gas Diffusion Electrode for High-Performance CO2 Electrochemical Reduction with Record CO Production Efficiency

Cu-In metallic hybrid is a promising non-noble catalyst for selective electrochemical CO₂ reduction (eCO₂R) to CO, but the lack of direct assembly with a gas diffusion electrode (GDE) limits the further development of eCO₂R to CO with both high Faradaic efficiency (FE) and high current density. In this study, an in situ electrochemical spontaneous precipitation (ESP) method was applied for the first time to prepare GDE-combined Cu-In electrocatalysts. The optimum Cu-In catalyst consists of a nanoscale "core-shell" structure of polycrystalline Cu_xO covered by the amorphous In(OH)₃ interface. Higher than 90% FE of CO production has been achieved. With the synergy of a GDE flow cell and 1 M KOH catholyte, a current density of ∼200 mA cm^-2 was reached at -1.17 V (reversible hydrogen electrode), which enabled a CO yield efficiency record of 3.05 mg min^-1(CO₂/15 mL min^-1 with a 2 cm² electrode). The ratios between CO and H₂ produced can be effectively modulated via fine-tuning ESP conditions demonstrating possibility of generating CO or syngas with tuneable ratios. The present study provides a simple approach for constructing novel catalytic interfaces with dual active centers for eCO₂R and other emerging electrochemical catalysis research.

Shining light on CO2: from materials discovery to photocatalyst, photoreactor and process engineering

Materials engineering, theoretical modelling, reactor engineering and process development of gas-phase photocatalytic CO₂ reduction exemplified by indium oxide systems.

A Z-scheme ZnIn2S4/Nb2O5 nanocomposite: constructed and used as an efficient bifunctional photocatalyst for H2 evolution and oxidation of 5-hydroxymethylfurfural

A bifunctional Z-scheme ZnIn₂S₄/Nb₂O₅ photocatalyst was fabricated, which can be used both for hydrogen evolution and HMF oxidation.

Hydrogen adsorption on In2O3(111) and In2O3(110)

DFT calculations are used to explore H₂ adsorption and dissociation on In₂O₃ surfaces.

Heterostructure Engineering of a Reverse Water Gas Shift Photocatalyst

To achieve substantial reductions in CO2 emissions, catalysts for the photoreduction of CO2 into value-added chemicals and fuels will most likely be at the heart of key renewable-energy technologies. Despite tremendous efforts, developing highly active and selective CO2 reduction photocatalysts remains a great challenge. Herein, a metal oxide heterostructure engineering strategy that enables the gas-phase, photocatalytic, heterogeneous hydrogenation of CO2 to CO with high performance metrics (i.e., the conversion rate of CO2 to CO reached as high as 1400 µmol g cat-1 h-1) is reported. The catalyst is comprised of indium oxide nanocrystals, In2O3- x (OH) y , nucleated and grown on the surface of niobium pentoxide (Nb2O5) nanorods. The heterostructure between In2O3- x (OH) y nanocrystals and the Nb2O5 nanorod support increases the concentration of oxygen vacancies and prolongs excited state (electron and hole) lifetimes. Together, these effects result in a dramatically improved photocatalytic performance compared to the isolated In2O3- x (OH) y material. The defect optimized heterostructure exhibits a 44-fold higher conversion rate than pristine In2O3- x (OH) y . It also exhibits selective conversion of CO2 to CO as well as long-term operational stability.

X-ray Photospectroscopy and Electronic Studies of Reactor Parameters on Photocatalytic Hydrogenation of Carbon Dioxide by Defect-Laden Indium Oxide Hydroxide Nanorods

In the study reported herein, glovebox-protected X-ray photoelectron spectroscopy (XPS) and in situ Hall charge carrier measurements provide new insights into the surface physical chemistry of gaseous H₂, CO₂, and H₂+CO₂ combined with nanostructured In₂O_(3−x)(OH)_y nanorods, which ensue under photochemical and thermochemical operating conditions. Heterolytic dissociation of H₂ in H₂-only atmosphere appears to occur mainly under dark and ambient temperature conditions, while the greatest amount of OH shoulder expansion in H₂+CO₂ atmosphere appears to mainly occur under photoilluminated conditions. These results correlate with those of the Hall measurements, which show that the prevalence of homolytic over heterolytic dissociation at increasing temperatures leads to a steeper rate of increase in carrier concentrations; and that H₂ adsorption is more prevalent than CO₂ in H₂+CO₂ photoillumination conditions.