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

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.

Topological transformation of LDH nanosheets to highly dispersed PtNiFe nanoalloys enhancing CO oxidation performance

Highly dispersed nanoalloys with a tailored metal-oxide interface are pivotal in developing advanced catalysts with superior performance for applications. Herein, a series of highly dispersed Pt/NiFeAl nanoalloys on amorphous supports were successfully fabricated by a topological transformation of layered-double-hydroxide nanosheets. With increasing reduction temperature, samples Pt/NiFeAl-x (x = reduction temperature) showed a progressive transformation from Pt/NiFeAl-LDH to a mixture (Pt, NiFe alloys, FeOy, and NiOy) supported on amorphous Al2O3, which eventually transformed to atomically dispersed PtNiFe alloys supported on amorphous Al2O3. Systematic sample characterization demonstrates that amorphous alumina-supported PtNiFe nanoalloys are merited by excellent redox ability, outstanding O2 activation ability, and moderate CO adsorption strength. When tested as catalysts for CO oxidation, all samples have demonstrated an apparent interfacial effect on catalytic performance, among which Pt/NiFeAl-600 shows a strikingly high CO oxidation activity at low-temperatures coupled with a broader operation temperature window (i.e. CO conversion >99.0%, 100-400 °C). Such a topological transformation strategy has proven applicable for generating atomically dispersed nanoalloys on amorphous supports for catalytic applications.

Solution-Liquid-Solid Growth and Catalytic Applications of Silica Nanorod Arrays

As an analogue to the vapor-liquid-solid process, the solution-liquid-solid (SLS) method offers a mild solution-phase route to colloidal 1D nanostructures with controlled sizes, compositions, and properties. However, direct growth of 1D nanostructure arrays through SLS processes remains in its infancy. Herein, this study shows that SLS processes are also suitable for the growth of nanorod arrays on the substrate. As a proof of concept, seedless growth of silica nanorod arrays on a variety of hydrophilic substrates such as pristine and oxide-modified glass, metal sheets, Si wafers, and biaxially oriented polypropylene film are demonstrated. Also, the silica nanorod arrays can be used as a new platform for the fabrication of catalysts for photothermal CO2 hydrogenation and the reduction of 4-nitrophenol reactions. This work offers some fundamental insight into the SLS growth process and opens a new avenue for the mild preparation of functional 1D nanostructure arrays for various applications.

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.

Zirconium-Based Metal-Organic Framework for Efficient Photocatalytic Reduction of CO2 to CO: The Influence of Doped Metal Ions

Recent developments have been highlighted for UiO-type materials, a class of metal-organic frameworks (MOFs) with high stability, as catalysts for photocatalytic CO₂ reduction. We design and synthesize two metal ion (Co²⁺, Re⁺)-doped UiO-67 as catalysts for the photocatalytic CO₂ reduction reaction and demonstrate that Co-UiO-67 exhibits better photocatalytic activity relative to Re-UiO-67. The superior photocatalytic activity of Co-UiO-67 over Re-UiO-67 results from the improved charge transportability and higher CO₂ adsorption capacity. Density functional theory (DFT) calculations reveal that the energy barrier of Co-UiO-67 (0.86 eV) for catalytic CO₂ reduction to CO is lower than that of Re-UiO-67 (0.92 eV), thus leading to superior photocatalytic performance of Co-UiO-67 than that of Re-UiO-67.

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.

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 .

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.

The reaction pathway of the CO2RR to low-carbon alcohols: a theoretical study

Catalytic hydrogenation of CO₂ to chemicals is an important approach for reducing the concentration of CO₂ in the atmosphere.

The synergistic role of the support surface and Au–Cu alloys in a plasmonic Au–Cu@LDH photocatalyst for the oxidative esterification of benzyl alcohol with methanol

The acid–base pairs of the support synergistic with Au–Cu alloy NPs could drive the oxidative esterification of benzyl alcohol with methanol.

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.

Ordered colloidal clusters constructed by nanocrystals with valence for efficient CO2 photoreduction

The ability to construct discrete colloidal clusters (CCs) as complex as molecular clusters is limited due to the lack of available colloidal building blocks and specific directional bonds. Here, we explore a strategy to organize anisotropic Prussian blue analog nanocrystals (NCs) toward CCs with open and highly ordered structures, experimentally realizing colloidal analogs to zeolitic clathrate structures. The directional interactions are derived from either crystallographic or morphological anisotropy of the NCs and achieved by the interplay of epitaxial growth, oriented attachment, and local packing. We attribute these interparticle interactions to enthalpic and entropic valences that imitate hybridized atomic orbitals of sp 3 d 2 octahedron and sp 3 d 3 f cube. Benefiting from the ordered multilevel porous structures, the obtained CCs exhibit greatly enhanced catalytic activity for CO2 photoreduction. Our work offers some fundamental insights into directional bonding among NCs and opens an avenue that promises access to unique CCs with unprecedented structures and applications.

Surface engineering of ultrasmall supported PdxBi nanoalloys with enhanced electrocatalytic activity for selective alcohol oxidation

Ultrasmall and homogeneous bimetallic PdxBi nanoalloys are well distributed on a Vulcan carbon support by a facile, low-cost synthetic strategy. The electrochemical activity of the as-prepared homogeneous PdxBi nanoalloy/carbon black nanocomposites is closely related to the content of Bi, revealing their excellent electrocatalytic performance for selective oxidation of monohydric alcohols and vicinal diols in alkali medium.

Amorphous MoO3-x nanosheets prepared by the reduction of crystalline MoO3 by Mo metal for LSPR and photothermal conversion

Amorphous MoO3-x with enhanced LSPR has been fabricated successfully by introducing Mo atoms into the interlayers of MoO3 nanosheets via a hydrothermal method. The inserted Mo atom could bond with inherent Mo atoms and further form a distorted atomic configuration structure. Thus, the amorphous MoO3-x possesses a relatively excellent photothermal conversion efficiency of 61.79%.

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.

Boosting Photocatalytic Hydrogen Production by Modulating Recombination Modes and Proton Adsorption Energy

Solar-driven production of renewable energy (e.g., H₂) has been investigated for decades. To date, the applications are limited by low efficiency due to rapid charge recombination (both radiative and nonradiative modes) and slow reaction rates. Tremendous efforts have been focused on reducing the radiative recombination and enhancing the interfacial charge transfer by engineering the geometric and electronic structure of the photocatalysts. However, fine-tuning of nonradiative recombination processes and optimization of target reaction paths still lack effective control. Here we show that minimizing the nonradiative relaxation and the adsorption energy of photogenerated surface-adsorbed hydrogen atoms are essential to achieve a longer lifetime of the charge carriers and a faster reaction rate, respectively. Such control results in a 16-fold enhancement in photocatalytic H₂ evolution and a 15-fold increase in photocurrent of the crystalline g-C₃N₄ compared to that of the amorphous g-C₃N₄.

Bismuth-Based Photocatalysts for Solar Photocatalytic Carbon Dioxide Conversion

Photocatalytic CO₂ conversion into solar fuels is an effective means for simultaneously solving both the greenhouse effect and energy crisis. In the past ten years, bismuth-based photocatalysts for environmental remediation have experienced a golden period of development. However, solar photocatalytic CO₂ conversion has only been developed over the past five years and, until now, no reviews have been published on bismuth-based photocatalysts for the photocatalytic conversion of CO₂ . For the first time, solar photocatalytic CO₂ conversion systems are reviewed herein. Synthetic methods and photocatalytic CO₂ performances of bismuth-based photocatalysts, including Sillén-structured BiOX (X=Cl, Br, I); Aurivillius-structured Bi₂ MO₆ (M=Mo, W); and Scheelite-structured BiVO₄ , Bi₂ S₃ , BiYO₃ , and BiOIO₃ , are summarized. In addition, activity-enhancing strategies for this photocatalyst family, including oxygen vacancies, bismuth-rich strategy, facet control, conventional type II heterojunction, Z-scheme heterojunction, and cocatalyst deposition, are reviewed. Finally, the main mechanistic research methods, such as in situ FTIR spectroscopy and theoretical calculations, are presented. Challenges and research trends reported in studies of bismuth-based photocatalysts for photocatalytic CO₂ conversion are discussed and summarized.

Living Atomically Dispersed Cu Ultrathin TiO2 Nanosheet CO2 Reduction Photocatalyst

Supported atomically dispersed metals are proving to be efficacious photocatalysts for CO2 reduction to solar fuels. While being atom efficient, they suffer from being noble, rare, and costly (Pt, Pd, Au, Ag, Rh) and lacking in long-term stability. Herein, all of these problems are solved with the discovery that atomically dispersed Cu supported on ultrathin TiO2 nanosheets can photocatalytically reduce an aqueous solution of CO2 to CO. The atomically dispersed Cu can be recycled in a straightforward procedure when they become oxidatively deactivated. This advance bodes well for the development of a solar fuels technology founded on abundant, low-cost, nontoxic, atomically dispersed metal photocatalysts.

Recent Advances in Direct Synthesis of Value-Added Aromatic Chemicals from Syngas by Cascade Reactions over Bifunctional Catalysts

Value-added aromatic monomers such as benzene, toluene, and xylenes (BTX) are very important building-block chemicals for the production of plastics, polymers, solvents, pesticides, dyes, and adhesives. Syngas-to-aromatics (STA) is a very promising approach for the synthesis of aromatic monomers, and is catalyzed via bifunctional catalysts in a single reactor, wherein methanol/dimethyl ether and/or olefins intermediates formed from syngas on metal components are converted into aromatic monomers exclusively on the HZSM-5 by cascade reactions. Since an optimal Fischer-Tropsch synthesis (FTS) temperature of Fe-based catalysts is very close to an aromatization temperature of HZSM-5, Fe-based catalysts have been frequently used/modified for the synthesis of aromatic monomers from hydrogenation of carbon oxides (CO and CO₂ ). The nature of metal components and amounts of Brönsted acid sites on HZSM-5, and their mesoporosity and intimacy, significantly alter the selectivity for aromatics by tuning BTX distibution and catalyst stability. Although many developments have been achieved regarding the STA process in recent years, no reviews have been published in this flourishing research area over the last two decades. Here, the recent advances and forthcoming challenges in the progress of syngas (CO+H₂ ) chemistry and hydrogenation of CO₂ toward the value-added aromatic monomers through cascade reactions are highlighted.

Nitrogen-Doped Carbon Cages Encapsulating CuZn Alloy for Enhanced CO2 Reduction

CuZn alloy, regarded as the active sites, shows excellent catalytic activity for the reverse water gas shift reaction, whereas the incorporation of N atoms, especially pyridinic N, can greatly improve its catalytic properties because of the strong promotion capacity for adsorption and activation of CO₂ molecules. Herein, the synthesis strategy involving Cu-doped Zn-based metal-organic frameworks is utilized to prepare CuZn alloy coated in an N-doped carbon shell. The excellent catalytic ability for CO₂ transformation originates from the synergistic catalytic effect between CuZn alloy and pyridinic N. The strong adsorption and activation capacity for CO₂ of pyridinic N is ascribed to the lone pair of electrons on the N atom and the high electron density in its vicinity.

Effect of Divalent Metals on the UV-Shielding Properties of MII/MgAl Layered Double Hydroxides

Both the particle size and compositions have a strong influence on the UV-shielding performance of layered double hydroxides (LDHs), and they will interact with each other. To investigate the effects of divalent metal ions on the UV-shielding properties of layered double hydroxides (LDHs), M^II/MgAl-CO₃ LDHs (M = Mg, Co, Ni, Cu, or Zn) with the same primary and secondary particle size have been prepared and their UV-shielding performance have been studied in this work. The UV-vis spectra show that the ZnMgAl-LDHs exhibit the highest absorbance under the ultraviolet B and ultraviolet A rays among these LDH samples, but in the ultraviolet C region, the CuMgAl-LDHs show the highest absorbance and this result is in good accordance with the UV-shielding performance, which was examined by protecting the photocatalytic degradation of rhodamine B aqueous solution. Moreover, under UV rays, PP/ZnMgAl-LDH films show excellent resistance to UV aging, which can be attributed to the strong inhibition of ZnMgAl-LDHs during the production of free radicals in polypropene, as has been confirmed by electron spin resonance results.

Selective light absorber-assisted single nickel atom catalysts for ambient sunlight-driven CO2 methanation

Ambient sunlight-driven CO₂ methanation cannot be realized due to the temperature being less than 80 °C upon irradiation with dispersed solar energy. In this work, a selective light absorber was used to construct a photothermal system to generate a high temperature (up to 288 °C) under weak solar irradiation (1 kW m⁻²), and this temperature is three times higher than that in traditional photothermal catalysis systems. Moreover, ultrathin amorphous Y₂O₃ nanosheets with confined single nickel atoms (SA Ni/Y₂O₃) were synthesized, and they exhibited superior CO₂ methanation activity. As a result, 80% CO₂ conversion efficiency and a CH₄ production rate of 7.5 L m⁻² h⁻¹ were achieved through SA Ni/Y₂O₃ under solar irradiation (from 0.52 to 0.7 kW m⁻²) when assisted by a selective light absorber, demonstrating that this system can serve as a platform for directly harnessing dispersed solar energy to convert CO₂ to valuable chemicals.

While light-driven CO₂ methanation provides a renewable means to upgrade waste emissions, the sunlight is insufficient to drive high temperature CO₂ methanation. Here, authors prepare single-atom Ni on Y₂O₃ with a selective light absorber for ambient-sunlight-driven photothermal CO₂ methanation.

Pd Single-Atom Catalysts on Nitrogen-Doped Graphene for the Highly Selective Photothermal Hydrogenation of Acetylene to Ethylene

The selective hydrogenation of acetylene to ethylene in an ethylene-rich gas stream is an important process in the chemical industry. Pd-based catalysts are widely used in this reaction due to their excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single-atom catalysts on nitrogen-doped graphene (Pd₁ /N-graphene) by a freeze-drying-assisted method is reported. The Pd₁ /N-graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C₂ H₂ with H₂ in the presence of excess C₂ H₄ under photothermal heating (UV and visible-light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C₂ H₄ hydrogenation. Importantly, the Pd₁ /N-graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar-driven photothermal catalyst systems based on single-atom active sites for selective hydrogenation reactions.

Solar-Driven Water-Gas Shift Reaction over CuOx /Al2 O3 with 1.1 % of Light-to-Energy Storage

Hydrogen production from coal gasification provides a cleaning approach to convert coal resource into chemical energy, but the key procedures of coal gasification and thermal catalytic water-gas shift (WGS) reaction in this energy technology still suffer from high energy cost. We herein propose adopting a solar-driven WGS process instead of traditional thermal catalysis, with the aim of greatly decreasing the energy consumption. Under light irradiation, the CuO_x /Al₂ O₃ delivers excellent catalytic activity (122 μmol g_cat ^-1  s^-1 of H₂ evolution and >95 % of CO conversion) which is even more efficient than noble-metal-based catalysts (Au/Al₂ O₃ and Pt/Al₂ O₃ ). Importantly, this solar-driven WGS process costs no electric/thermal power but attains 1.1 % of light-to-energy storage. The attractive performance of the solar-driven WGS reaction over CuO_x /Al₂ O₃ can be attributed to the combined photothermocatalysis and photocatalysis.

Two-dimensional-related catalytic materials for solar-driven conversion of COx into valuable chemical feedstocks

The discovery of improved chemical processes for CO and CO2 hydrogenation to valuable hydrocarbon fuels and alcohols is of paramount importance for the chemical industry. Such technologies have the potential to reduce anthropogenic CO2 emissions by adding value to a waste stream, whilst also reducing our consumption of fossil fuels. Current thermal catalytic technologies available for CO and CO2 hydrogenation are demanding in terms of energy input. Various alternative technologies are now being developed for COx hydrogenation, with solar-driven processes over two-dimensional (2D) and 2D-related composite materials being particularly attractive due to the abundance of solar energy on Earth and also the high selectivity of defect-engineered 2D materials towards specific valuable products under very mild reaction conditions. This review showcases recent advances in the solar-driven COx reduction to hydrocarbons over 2D-based materials. Optimization of 2D catalyst performance demands interdisciplinary research that embraces catalyst electronic structure manipulation and morphology control, surface/interface engineering, reactor engineering and density functional theory modelling studies. Through improved understanding of the structure-performance relationships in 2D-related catalysts which is achievable through the application of modern in situ characterization techniques, practical photo/photothermal/photoelectrochemical technologies for CO and CO2 reduction to high-valuable products such as olefins could be realized in the not-too-distant future.

Core-Shell Prussian Blue Analogs with Compositional Heterogeneity and Open Cages for Oxygen Evolution Reaction

Here, a reduction-cation exchange (RCE) strategy is proposed for synthesizing Fe-Co based bimetallic Prussian blue analogs (PBAs) with heterogeneous composition distribution and open cage nanocage architecture. Specially, bivalent cobalt is introduced into a potassium ferricyanide solution containing hydrochloric acid and polyvinyl pyrrolidone. The uniform PBAs with opened cages are formed tardily after hydrothermal reaction. Time-dependent evolution characterization on composition elucidating the RCE mechanism is based on the sequential reduction of ferric iron and cation exchange reaction between divalent iron and cobalt. The PBA structures are confirmed by electron tomography technology, and the heterogeneous element distribution is verified by energy-dispersive X-ray spectroscopy elemental analysis, leading to the formation of core-shell PBAs with compositional heterogeneity (Fe rich shell and Co rich core) and open cage architecture. When the PBA catalysts are used to boost the oxygen evolution reaction (OER), superior OER activity and long-term stability (low overpotential of 271 mV at 10 mA cm-2 and ≈5.3% potential increase for 24 h) are achieved, which is attributed to the unique compositional and structural properties as well as high special surface areas (576.2 m2 g-1). The strategies offer insights for developing PBAs with compositional and structural multiplicity, which encourages more practical catalytic applications.