Visible and Near-Infrared Photothermal Catalyzed Hydrogenation of Gaseous CO2 over Nanostructured Pd@Nb2O5

A Ni-O-Ag photothermal catalyst enables 103-m2 artificial photosynthesis with >17% solar-to-chemical energy conversion efficiency

The scalable artificial photosynthesis composed of photovoltaic electrolysis and photothermal catalysis is limited by inefficient photothermal CO2 hydrogenation under weak sunlight irradiation. Herein, NiO nanosheets supported with Ag single atoms [two-dimensional (2D) Ni1Ag0.02O1] are synthesized for photothermal CO2 hydrogenation to achieve 1065 mmol g-1 hour-1 of CO production rate under 1-sun irradiation. This performance is attributed to the coupling effect of Ag-O-Ni sites to enhance the hydrogenation of CO2 and weaken the CO adsorption, resulting in 1434 mmol g-1 hour-1 of CO yield at 300°C. Furthermore, we integrate the 2D Ni1Ag0.02O1-supported photothermal reverse water-gas shift reaction with commercial photovoltaic electrolytic water splitting to construct a 103-m2 scale artificial photosynthesis system (CO2 + H2O → CO + H2 + O2), which achieves more than 22 m3/day of green syngas with an adjustable H2/CO ratio (0.4-3) and a photochemical energy conversion efficiency of >17%. This research charts a promising course for designing practical, natural sunlight-driven artificial photosynthesis systems.

Conjugated Microporous Polymers for Catalytic CO2 Conversion

Rising carbon dioxide (CO2) levels in the atmosphere are recognized as a threat to atmospheric stability and life. Although this greenhouse gas is being produced on a large scale, there are solutions to reduction and indeed utilization of the gas. Many of these solutions involve costly or unstable technologies, such as air-sensitive metal-organic frameworks (MOFs) for CO2 capture or "non-green" systems such as amine scrubbing. Conjugated microporous polymers (CMPs) represent a simpler, cheaper, and greener solution to CO2 capture and utilization. They are often easy to synthesize at scale (a one pot reaction in many cases), chemically and thermally stable (especially in comparison with their MOF and covalent organic framework (COF) counterparts, owing to their amorphous nature), and, as a result, cheap to manufacture. Furthermore, their large surface areas, tunable porous frameworks and chemical structures mean they are reported as highly efficient CO2 capture motifs. In addition, they provide a dual pathway to utilize captured CO2 via chemical conversion or electrochemical reduction into industrially valuable products. Recent studies show that all these attractive properties can be realized in metal-free CMPs, presenting a truly green option. The promising results in these two fields of CMP applications are reviewed and explored here.

A nonmetallic plasmonic catalyst for photothermal CO2 flow conversion with high activity, selectivity and durability

The meticulous design of active sites and light absorbers holds the key to the development of high-performance photothermal catalysts for CO2 hydrogenation. Here, we report a nonmetallic plasmonic catalyst of Mo2N/MoO2-x nanosheets by integrating a localized surface plasmon resonance effect with two distinct types of active sites for CO2 hydrogenation. Leveraging the synergism of dual active sites, H2 and CO2 molecules can be simultaneously adsorbed and activated on N atom and O vacancy, respectively. Meanwhile, the plasmonic effect of this noble-metal-free catalyst signifies its promising ability to convert photon energy into localized heat. Consequently, Mo2N/MoO2-x nanosheets exhibit remarkable photothermal catalytic performance in reverse water-gas shift reaction. Under continuous full-spectrum light irradiation (3 W·cm-2) for a duration of 168 h, the nanosheets achieve a CO yield rate of 355 mmol·gcat-1·h-1 in a flow reactor with a selectivity exceeding 99%. This work offers valuable insights into the precise design of noble-metal-free active sites and the development of plasmonic catalysts for reducing carbon footprints.

Recent Advances of Constructing Metal/Semiconductor Catalysts Designing for Photocatalytic CO2 Hydrogenation

With the development of the world economy and the rapid advancement of global industrialization, the demand for energy continues to grow. The significant consumption of fossil fuels, such as oil, coal, and natural gas, has led to excessive carbon dioxide emissions, causing global ecological problems. CO2 hydrogenation technology can convert CO2 into high-value chemicals and is considered one of the potential ways to solve the problem of CO2 emissions. Metal/semiconductor catalysts have shown good activity in carbon dioxide hydrogenation reactions and have attracted widespread attention. Therefore, we summarize the recent research on metal/semiconductor catalysts for photocatalytic CO2 hydrogenation from the design of catalysts to the structure of active sites and mechanistic investigations, and the internal mechanism of the enhanced activity is elaborated to give guidance for the design of highly active catalysts. Finally, based on a good understanding of the above issues, this review looks forward to the development of future CO2 hydrogenation catalysts.

Cu-based high-entropy two-dimensional oxide as stable and active photothermal catalyst

Cu-based nanocatalysts are the cornerstone of various industrial catalytic processes. Synergistically strengthening the catalytic stability and activity of Cu-based nanocatalysts is an ongoing challenge. Herein, the high-entropy principle is applied to modify the structure of Cu-based nanocatalysts, and a PVP templated method is invented for generally synthesizing six-eleven dissimilar elements as high-entropy two-dimensional (2D) materials. Taking 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x as an example, the high-entropy structure not only enhances the sintering resistance from 400 °C to 800 °C but also improves its CO₂ hydrogenation activity to a pure CO production rate of 417.2 mmol g^-1 h^-1 at 500 °C, 4 times higher than that of reported advanced catalysts. When 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x are applied to the photothermal CO₂ hydrogenation, it exhibits a record photochemical energy conversion efficiency of 36.2%, with a CO generation rate of 248.5 mmol g^-1 h^-1 and 571 L of CO yield under ambient sunlight irradiation. The high-entropy 2D materials provide a new route to simultaneously achieve catalytic stability and activity, greatly expanding the application boundaries of photothermal catalysis.

Photothermal Catalytic CO2 Conversion: Beyond Catalysis and Photocatalysis

In recent years, the combination of both thermal and photochemical contributions has provided interesting opportunities for solar upgrading of catalytic processes. Photothermal catalysis works at the interface between purely photochemical processes, which involve the direct conversion of photon energy into chemical energy, and classical thermal catalysis, in which the catalyst is activated by temperature. Thus, photothermal catalysis acts in two different ways on the energy path of the reaction. This combined catalysis, of which the fundamental principles will be reviewed here, is particularly promising for the activation of small reactive molecules at moderate temperatures compared to thermal catalysis and with higher reaction rates than those attained in photocatalysis, and it has gained a great deal of attention in the last years. Among the different applications of photothermal catalysis, CO₂ conversion is probably the most studied, although reaction mechanisms and photonic-thermal synergy pathways are still quite unclear and, from the reaction route point of view, it can be said that photothermal-catalytic CO₂ reduction processes are still in their infancy. This article intends to provide an overview of the principles underpinning photothermal catalysis and its application to the conversion of CO₂ into useful molecules, with application essentially as fuels but also as chemical building blocks. The most relevant specific cases published to date will be also reviewed from the viewpoint of selectivity towards the most frequent target products.

Recent Advances in Graphitic Carbon Nitride Based Electro-Catalysts for CO2 Reduction Reactions

The electrocatalytic carbon dioxide reduction reaction is an effective means of combating the greenhouse effect caused by massive carbon dioxide emissions. Carbon nitride in the graphitic phase (g-C₃N₄) has excellent chemical stability and unique structural properties that allow it to be widely used in energy and materials fields. However, due to its relatively low electrical conductivity, to date, little effort has been made to summarize the application of g-C₃N₄ in the electrocatalytic reduction of CO₂. This review focuses on the synthesis and functionalization of g-C₃N₄ and the recent advances of its application as a catalyst and a catalyst support in the electrocatalytic reduction of CO₂. The modification of g-C₃N₄-based catalysts for enhanced CO₂ reduction is critically reviewed. In addition, opportunities for future research on g-C₃N₄-based catalysts for electrocatalytic CO₂ reduction are discussed.

Niche Applications of MXene Materials in Photothermal Catalysis

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis.

Sunlight-Powered Reverse Water Gas Shift Reaction Catalysed by Plasmonic Au/TiO2 Nanocatalysts: Effects of Au Particle Size on the Activity and Selectivity

This study reports the low temperature and low pressure conversion (up to 160 °C, p = 3.5 bar) of CO₂ and H₂ to CO using plasmonic Au/TiO₂ nanocatalysts and mildly concentrated artificial sunlight as the sole energy source (up to 13.9 kW·m^-2 = 13.9 suns). To distinguish between photothermal and non-thermal contributors, we investigated the impact of the Au nanoparticle size and light intensity on the activity and selectivity of the catalyst. A comparative study between P25 TiO₂-supported Au nanocatalysts of a size of 6 nm and 16 nm displayed a 15 times higher activity for the smaller particles, which can only partially be attributed to the higher Au surface area. Other factors that may play a role are e.g., the electronic contact between Au and TiO₂ and the ratio between plasmonic absorption and scattering. Both catalysts displayed ≥84% selectivity for CO (side product is CH₄). Furthermore, we demonstrated that the catalytic activity of Au/TiO₂ increases exponentially with increasing light intensity, which indicated the presence of a photothermal contributor. In dark, however, both Au/TiO₂ catalysts solely produced CH₄ at the same catalyst bed temperature (160 °C). We propose that the difference in selectivity is caused by the promotion of CO desorption through charge transfer of plasmon generated charges (as a non-thermal contributor).

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

Thermo-photo catalysis: a whole greater than the sum of its parts

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.

Photothermal Chemistry Based on Solar Energy: From Synergistic Effects to Practical Applications

With the development of society, energy shortage and environmental problems have become more and more outstanding. Solar energy is a clean and sustainable energy resource, potentially driving energy conversion and environmental remediation reactions. Thus, solar-driven chemistry is an attractive way to solve the two problems. Photothermal chemistry (PTC) is developed to achieve full-spectral utilization of the solar radiation and drive chemical reactions more efficiently under relatively mild conditions. In this review, the mechanisms of PTC are summarized from the aspects of thermal and non-thermal effects, and then the interaction and synergy between these two effects are sorted out. In this paper, distinguishing and quantifying these two effects is discussed to understand PTC processes better and to design PTC catalysts more methodically. However, PTC is still a little far away from practical. Herein, several key points, which must be considered when pushing ahead with the engineering application of PTC, are proposed, along with some workable suggestions on the practical application. This review provides a unique perspective on PTC, focusing on the synergistic effects and pointing out a possible direction for practical application.

Bismuth single atom supported CeO2 nanosheets for oxidation resistant photothermal reverse water gas shift reaction

Bi single atoms supported on CeO2 nanosheets combined with a Ti2O3 based photothermal device showed oxidation resistance and outperforming weak solar driven RWGS with a CO production rate of 31.00 mmol g−1 h−1 under 3 sun units of irradiation.

Tunable Selectivity in CO2 Photo-Thermal Reduction by Perovskite-Supported Pd Nanoparticles

Photo-thermal catalysis has recently emerged as a promising alternative to overcome the limitations of traditional photocatalysis. Despite its potential, most of the photo-thermal systems still lack adequate selectivity patterns and appropriate analysis of the underlying reaction pathways, thus hampering a wide implementation. Herein, a novel photocatalyst based on Pd nanoparticles (NPs) supported on barium titanate (BTO) was prepared for the selective photo-thermal reduction of CO₂ and displayed catalytic rates of up to 8.2 mol_CO  g_Pd ^-1  h^-1 . The photocatalyst allowed for a tailored selectivity towards CO or CH₄ as a function of the metal loading or the light intensity. Mechanistic studies indicated that both thermal and non-thermal contributions of light played a role in the overall reaction pathway, each of them being dominant upon changing reaction conditions.

Solar Urea: Towards a Sustainable Fertilizer Industry

Urea, an agricultural fertilizer, nourishes humanity. The century-old Bosch-Meiser process provides the world's urea. It is multi-step, consumes enormous amounts of non-renewable energy, and has a large CO₂ footprint. Thus, developing an eco-friendly synthesis for urea is a priority. Herein we report a single-step Pd/LTA-3A catalyzed synthesis of urea from CO₂ and NH₃ under ambient conditions powered solely by solar energy. Pd nanoparticles serve the dual function of catalyzing the dissociation of NH₃ and providing the photothermal driving force for urea formation, while the absorption capacity of LTA-3A removes by-product H₂ O to shift the equilibrium towards urea production. The solar urea conversion rate from NH₃ and CO₂ is 87 μmol g^-1  h^-1 . This advance represents a first step towards the use of solar energy in urea production. It provides insights into green fertilizer production, and inspires the vision of sustainable, modular plants for distributed production of urea on farms.

Highlights and challenges in the selective reduction of carbon dioxide to methanol

Carbon dioxide (CO₂) is the iconic greenhouse gas and the major factor driving present global climate change, incentivizing its capture and recycling into valuable products and fuels. The 6H⁺/6e^- reduction of CO₂ affords CH₃OH, a key compound that is a fuel and a platform molecule. In this Review, we compare different routes for CO₂ reduction to CH₃OH, namely, heterogeneous and homogeneous catalytic hydrogenation, as well as enzymatic catalysis, photocatalysis and electrocatalysis. We describe the leading catalysts and the conditions under which they operate, and then consider their advantages and drawbacks in terms of selectivity, productivity, stability, operating conditions, cost and technical readiness. At present, heterogeneous hydrogenation catalysis and electrocatalysis have the greatest promise for large-scale CO₂ reduction to CH₃OH. The availability and price of sustainable electricity appear to be essential prerequisites for efficient CH₃OH synthesis.

Nb2O5-Based Photocatalysts

Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is eco-friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Brønsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5-based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5-based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.

Plasmonic photothermal catalysis for solar-to-fuel conversion: current status and prospects

Solar-to-fuel conversion through photocatalytic processes is regarded as promising technology with the potential to reduce reliance on dwindling reserves of fossil fuels and to support the sustainable development of our society. However, conventional semiconductor-based photocatalytic systems suffer from unsatisfactory reaction efficiencies due to limited light harvesting abilities. Recent pioneering work from several groups, including ours, has demonstrated that visible and infrared light can be utilized by plasmonic catalysts not only to induce local heating but also to generate energetic hot carriers for initiating surface catalytic reactions and/or modulating the reaction pathways, resulting in synergistically promoted solar-to-fuel conversion efficiencies. In this perspective, we focus primarily on plasmon-mediated catalysis for thermodynamically uphill reactions converting CO2 and/or H2O into value-added products. We first introduce two types of mechanism and their applications by which reactions on plasmonic nanostructures can be initiated: either by photo-induced hot carriers (plasmonic photocatalysis) or by light-excited phonons (photothermal catalysis). Then, we emphasize examples where the hot carriers and phonon modes act in concert to contribute to the reaction (plasmonic photothermal catalysis), with special attention given to the design concepts and reaction mechanisms of the catalysts. We discuss challenges and future opportunities relating to plasmonic photothermal processes, aiming to promote an understanding of underlying mechanisms and provide guidelines for the rational design and construction of plasmonic catalysts for highly efficient solar-to-fuel conversion.

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.

Fundamentals and applications of photo-thermal catalysis

Photo-thermal catalysis has recently emerged as an alternative route to drive chemical reactions using light as an energy source.

Engineering Heterostructured Nanocatalysts for CO2 Transformation Reactions: Advances and Perspectives

As a conceivable route to achieving anthropological carbon looping, carbon capture and utilization (CCU) technologies employ waste CO₂ as an accessible C1 building block to generate upgraded chemicals or fuels, thereby simultaneously remedying environmental issues and energy crises. However, efficient CO₂ conversion is disfavored by both its thermodynamics and its kinetics. Heterostructured materials with well-controlled interfaces have great potential for enhanced catalytic performance in various CO₂ transformation reactions, owing to the synergistic effects among components, numerous interfacial and/or surface active sites, increased CO₂ adsorption capacity, promoted charge transfer efficiency, and unique physicochemical properties. This Review highlights the state of the art in typical heterostructures, such as core-shell, yolk-shell, Janus, hierarchical (branched and hollow), and 2D/2D layered structures, applied for CO₂ conversion with various energy inputs (radiation, electricity, heat). Fabrication methods of different heterostructures and structure-composition-performance relationships are also discussed concisely. Finally, a brief summary and prospective research directions are provided. The motivation of this Review is to offer instructive information on the applicability of inorganic heterostructures for CO₂ transformation reactions, and it is hoped that further enlightening studies in this field could emerge in the future.

Bismuth atom tailoring of indium oxide surface frustrated Lewis pairs boosts heterogeneous CO2 photocatalytic hydrogenation

The surface frustrated Lewis pairs (SFLPs) on defect-laden metal oxides provide catalytic sites to activate H₂ and CO₂ molecules and enable efficient gas-phase CO₂ photocatalysis. Lattice engineering of metal oxides provides a useful strategy to tailor the reactivity of SFLPs. Herein, a one-step solvothermal synthesis is developed that enables isomorphic replacement of Lewis acidic site In³⁺ ions in In₂O₃ by single-site Bi³⁺ ions, thereby enhancing the propensity to activate CO₂ molecules. The so-formed Bi_xIn_2-xO₃ materials prove to be three orders of magnitude more photoactive for the reverse water gas shift reaction than In₂O₃ itself, while also exhibiting notable photoactivity towards methanol production. The increased solar absorption efficiency and efficient charge-separation and transfer of Bi_xIn_2-xO₃ also contribute to the improved photocatalytic performance. These traits exemplify the opportunities that exist for atom-scale engineering in heterogeneous CO₂ photocatalysis, another step towards the vision of the solar CO₂ refinery.

Surface frustrated Lewis pairs (SFLPs) provide a unique class of active sites that enable efficient gas-phase CO₂ photocatalysis. How to tailor the reactivity of the SFLPs represents a major challenge, which the authors address here by single-site Bi³⁺ ion substitution of the SFLPs.

High-performance light-driven heterogeneous CO2 catalysis with near-unity selectivity on metal phosphides

Akin to single-site homogeneous catalysis, a long sought-after goal is to achieve reaction site precision in heterogeneous catalysis for chemical control over patterns of activity, selectivity and stability. Herein, we report on metal phosphides as a class of material capable of realizing these attributes and unlock their potential in solar-driven CO₂ hydrogenation. Selected as an archetype, Ni₁₂P₅ affords a structure based upon highly dispersed nickel nanoclusters integrated into a phosphorus lattice that harvest light intensely across the entire solar spectral range. Motivated by its panchromatic absorption and unique linearly bonded nickel-carbonyl-dominated reaction route, Ni₁₂P₅ is found to be a photothermal catalyst for the reverse water gas shift reaction, offering a CO production rate of 960 ± 12 mmol g_cat⁻¹ h⁻¹, near 100% selectivity and long-term stability. Successful extension of this idea to Co₂P analogs implies that metal phosphide materials are poised as a universal platform for high-rate and highly selective photothermal CO₂ catalysis.

There exists an urgent need to develop new materials to convert CO₂ to useful products. Here, authors demonstrate metal phosphide nanoparticles to enable light-driven CO₂ hydrogenation with high activities and near-unity selectivity.

MOF-Templated Preparation of Highly Dispersed Co/Al2O3 Composite as the Photothermal Catalyst with High Solar-to-Fuel Efficiency for CO2 Methanation

CH₄ production from CO₂ hydrogenation provides a clean approach to convert greenhouse gas CO₂ into chemical energy, but high energy consumption in this reaction still restrains its further application. Herein, we use a light-driven CO₂ methanation process instead of traditional thermocatalysis by an electrical heating mode, with the aim of greatly decreasing the energy consumption. Under UV-vis-IR light irradiation, the photothermal CO₂ methanation over highly dispersed Co nanoparticles supported on Al₂O₃ (Co/Al₂O₃) achieves impressive CH₄ production rates (as high as 6036 μmol g^-1 h^-1), good CH₄ selectivity (97.7%), and catalytic durability. The high light-harvesting property of the catalyst across the entire solar spectrum coupled with its strong adsorption capacity toward H₂, CO₂, CO, and abundant active sites are proposed to be responsible for the better photothermocatalytic performance of Co/Al₂O₃. Furthermore, a novel light-promotion effect is also revealed in CO₂ methanation, where UV-vis light irradiation induces oxygen vacancies and improves the proclivity toward adsorption of H₂, CO₂, and CO, finally resulting in a significant enhancement of the photothermocatalytic activity for CH₄ production. By concentrating the low-intensity light (120 mW/cm²) via a Fresnel lens, a photothermal CO₂ conversion efficiency of more than 50% with a good CH₄ selectivity (76%) is achieved on the optimal catalyst under a dynamic reaction system, which indicates the bright prospect of photothermal CO₂ methanation.

Recent Advances in Solar-Driven Carbon Dioxide Conversion: Expectations versus Reality

Solar-driven carbon dioxide (CO₂) conversion to fuels and high-value chemicals can contribute to the better utilization of renewable energy sources. Photosynthetic (PS), photocatalytic (PC), photoelectrochemical (PEC), and photovoltaic plus electrochemical (PV+EC) approaches are intensively studied strategies. We aimed to compare the performance of these approaches using unified metrics and to highlight representative studies with outstanding performance in a given aspect. Most importantly, a statistical analysis was carried out to compare the differences in activity, selectivity, and durability of the various approaches, and the underlying causes are discussed in detail. Several interesting trends were found: (i) Only the minority of the studies present comprehensive metrics. (ii) The CO₂ reduction products and their relative amount vary across the different approaches. (iii) Only the PV+EC approach is likely to lead to industrial technologies in the midterm future. Last, a brief perspective on new directions is given to stimulate discussion and future research activity.

Cobalt Plasmonic Superstructures Enable Almost 100% Broadband Photon Efficient CO2 Photocatalysis

The efficiency of heterogeneous photocatalysis for converting solar to chemical energy is low on a per photon basis mainly because of the difficulty of capturing and utilizing light across the entire solar spectral wavelength range. This challenge is addressed herein with a plasmonic superstructure, fashioned as an array of nanoscale needles comprising cobalt nanocrystals assembled within a sheath of porous silica grown on a fluorine tin oxide substrate. This plasmonic superstructure can strongly absorb sunlight through different mechanisms including enhanced plasmonic excitation by the hybridization of Co nanoparticles in close proximity, as well as inter- and intra-band transitions. With nearly 100% sunlight harvesting ability, it drives the photothermal hydrogenation of carbon dioxide with a 20-fold rate increase from the silica-supported cobalt catalyst. The present work bridges the gap between strong light-absorbing plasmonic superstructures with photothermal CO₂ catalysis toward the complete utilization of the solar energy.

Black indium oxide a photothermal CO2 hydrogenation catalyst

Nanostructured forms of stoichiometric In₂O₃ are proving to be efficacious catalysts for the gas-phase hydrogenation of CO₂. These conversions can be facilitated using either heat or light; however, until now, the limited optical absorption intensity evidenced by the pale-yellow color of In₂O₃ has prevented the use of both together. To take advantage of the heat and light content of solar energy, it would be advantageous to make indium oxide black. Herein, we present a synthetic route to tune the color of In₂O₃ to pitch black by controlling its degree of non-stoichiometry. Black indium oxide comprises amorphous non-stoichiometric domains of In₂O_3-x on a core of crystalline stoichiometric In₂O₃, and has 100% selectivity towards the hydrogenation of CO₂ to CO with a turnover frequency of 2.44 s^-1.

Synergizing Photo-Thermal H2 and Photovoltaics into a Concentrated Sunlight Use

Solar hydrogen and electricity are promising high energy-density renewable sources. Although photochemistry or photovoltaics are attractive routes, special challenge arises in sunlight conversion efficiency. To improve efficiency, various semiconductor materials have been proposed with selective sunlight absorption. Here, we reported a hybrid system synergizing photo-thermochemical hydrogen and photovoltaics, harvesting full-spectrum sunlight in a cascade manner. A simple suspension of Au-TiO₂ in water/methanol serves as a spectrum selector, absorbing ultraviolet-visible and infrared energy for rapid photo-thermochemical hydrogen production. The transmitted visible and near-infrared energy fits the photovoltaic bandgap and retains the high efficiency of a commercial photovoltaic cell under different solar concentration values. The experimental design achieved an overall efficiency of 4.2% under 12 suns solar concentration. Furthermore, the results demonstrated a reduced energy loss in full-spectrum energy conversion into hydrogen and electricity. Such simple integration of photo-thermochemical hydrogen and photovoltaics would create a pathway toward cascading use of sunlight energy.

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An integration of both photothermal H₂ and PV was proposed at full solar spectrum

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Absorbed UV-vis and IR generate H₂ faster than reported full-spectrum catalysis

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Transmitted Vis and near-IR bands retain the high efficiency of commercial PV cells

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A novel device was designed with experimental overall efficiency of 4.2% at 12 suns

Coupling of Solar Energy and Thermal Energy for Carbon Dioxide Reduction: Status and Prospects

Enormous efforts have been devoted to the reduction of carbon dioxide (CO₂ ) by utilizing various driving forces, such as heat, electricity, and radiation. However, the efficient reduction of CO₂ is still challenging because of sluggish kinetics. Recent pioneering studies from several groups, including us, have demonstrated that the coupling of solar energy and thermal energy offers a novel and promising strategy to promote the activity and/or manipulate selectivity in CO₂ reduction. Herein, we clarify the definition and principles of coupling solar energy and thermal energy, and comprehensively review the status and prospects of CO₂ reduction by coupling solar energy and thermal energy. Catalyst design, reactor configuration, photo-mediated activity/selectivity, and mechanism studies in photo-thermo CO₂ reduction will be emphasized. The aim of this Review is to promote understanding towards CO₂ activation and provide guidelines for the design of new catalysts for the efficient reduction of CO₂ .

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Reduction of carbon dioxide on photoexcited nanoparticles of VIII group metals

The photocatalytic reduction of carbon dioxide on nanoparticles of group VIII transition metals represents an emerging research area in recent years because of their promise in transforming carbon dioxide, a greenhouse gas, into value-added chemicals and fuels with the energy input of light. This mini review summarizes the fundamentals of the reduction of carbon dioxide and addresses how the photoexcitation of the metal nanoparticles can influence the reactions. The important roles of non-thermal hot electrons and photothermal effect in the photocatalytic reduction of carbon dioxide are highlighted, and the recent research reported in the literature are overviewed. There are still challenges in characterizing the photocatalytic reactions to distinguish the contributions of non-thermal and photothermal effects.

Polymorph selection towards photocatalytic gaseous CO2 hydrogenation

Titanium dioxide is the only known material that can enable gas-phase CO₂ photocatalysis in its anatase and rutile polymorphic forms. Materials engineering of polymorphism provides a useful strategy for optimizing the performance metrics of a photocatalyst. In this paper, it is shown that the less well known rhombohedral polymorph of indium sesquioxide, like its well-documented cubic polymorph, is a CO₂ hydrogenation photocatalyst for the production of CH₃OH and CO. Significantly, the rhombohedral polymorph exhibits higher activity, superior stability and improved selectivity towards CH₃OH over CO. These gains in catalyst performance originate in the enhanced acidity and basicity of surface frustrated Lewis pairs in the rhombohedral form.

Polymorphs, compounds with identical chemical stoichiometries yet different atomic configurations, expand the range of potential chemical properties and new applications. Here, authors show rhombohedral indium oxides to be highly active and selective for photocatalytic CO₂ hydrogenation.

Towards Solar Methanol: Past, Present, and Future

This work aims to provide an overview of producing value-added products affordably and sustainably from greenhouse gases (GHGs). Methanol (MeOH) is one such product, and is one of the most widely used chemicals, employed as a feedstock for ≈30% of industrial chemicals. The starting materials are analogous to those feeding natural processes: water, CO2, and light. Innovative technologies from this effort have global significance, as they allow GHG recycling, while providing society with a renewable carbon feedstock. Light, in the form of solar energy, assists the production process in some capacity. Various solar strategies of continually increasing technology readiness levels are compared to the commercial MeOH process, which uses a syngas feed derived from natural gas. These strategies include several key technologies, including solar-thermochemical, photochemical, and photovoltaic-electrochemical. Other solar-assisted technologies that are not yet commercial-ready are also discussed. The commercial-ready technologies are compared using a technoeconomic analysis, and the scalability of solar reactors is also discussed in the context of light-incorporating catalyst architectures and designs. Finally, how MeOH compares against other prospective products is briefly discussed, as well as the viability of the most promising solar MeOH strategy in an international context.

Pd@H yWO3- x Nanowires Efficiently Catalyze the CO2 Heterogeneous Reduction Reaction with a Pronounced Light Effect

The design of photocatalysts able to reduce CO₂ to value-added chemicals and fuels could enable a closed carbon circular economy. A common theme running through the design of photocatalysts for CO₂ reduction is the utilization of semiconductor materials with high-energy conduction bands able to generate highly reducing electrons. Far less explored in this respect are low-energy conduction band materials such as WO₃. Specifically, we focus attention on the use of Pd nanocrystal decorated WO₃ nanowires as a heretofore-unexplored photocatalyst for the hydrogenation of CO₂. Powder X-ray diffraction, thermogravimetric analysis, ultraviolet-visible-near infrared, and in situ X-ray photoelectron spectroscopy analytical techniques elucidate the hydrogen tungsten bronze, H _yWO_{3- x}, as the catalytically active species formed via the H₂ spillover effect by Pd. The existence in H _yWO_{3- x} of Brønsted acid hydroxyls OH, W(V) sites, and oxygen vacancies (V_O) facilitate CO₂ capture and reduction reactions. Under solar irradiation, CO₂ reduction attains CO production rates as high as 3.0 mmol g_cat^-1 hr^-1 with a selectivity exceeding 99%. A combination of reaction kinetic studies and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements provide a valuable insight into thermochemical compared to photochemical surface reaction pathways, considered responsible for the hydrogenation of CO₂ by Pd@H _yWO_{3- x}.

Light-driven thermocatalytic CO2 reduction over surface-passivated β-Mo2C nanowires: enhanced catalytic stability by light

As compared to the thermocatalysis without light irradiation, the catalytic stability of P-Mo₂C in the light-driven thermocatalysis is significantly improved.

Emerging Applications of Plasmons in Driving CO2 Reduction and N2 Fixation

The photochemical production of fuels using sunlight is an innovative way for meeting the quickly increasing energy demands. One of the largest challenges is to develop high-performance photocatalysts that can meet the requirements of practical applications. Owing to their intriguing localized surface plasmon resonances, noble metal nanoparticles and nanostructures show a great potential for enhancing the photocatalytic efficiency and thereby have attracted rapidly growing interest recently. Here, for the first time, the latest achievements in the utilization of plasmons in driving CO₂ reduction and N₂ fixation into high-value products are comprehensively described. The involved plasmonic enhancement mechanisms in the two types of reactions are fully illustrated. A particular emphasis is given to the outlook on the direction and prospects for future work in this topic.

Alumina-Supported CoFe Alloy Catalysts Derived from Layered-Double-Hydroxide Nanosheets for Efficient Photothermal CO2 Hydrogenation to Hydrocarbons

A series of novel CoFe-based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered-double-hydroxide (LDH) nanosheets at 300-700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe-x) are highly dependent on the reduction temperature (x). CO₂ hydrogenation experiments are conducted on the CoFe-x catalysts under UV-vis excitation. With increasing LDH-nanosheet reduction temperature, the CoFe-x catalysts show a progressive selectivity shift from CO to CH₄ , and eventually to high-value hydrocarbons (C₂₊ ). CoFe-650 shows remarkable selectivity toward hydrocarbons (60% CH₄ , 35% C₂₊ ). X-ray absorption fine structure, high-resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina-supported CoFe-alloy nanoparticles are responsible for the high selectivity of CoFe-650 for C₂₊ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar-energy to produce valuable chemicals and fuels from CO₂ .