Efficiency Of Photocatalytic CO2 Reduction Research Articles

Surface Coordination Environment Engineering on PtxCu1-x Alloy Catalysts for the Efficient Photocatalytic Reduction of CO2 to CH4.

Alloy catalysts have been reported to be robust in catalyzing various heterogeneous reactions due to the synergistic effect between different metal atoms. In this work, aimed at understanding the effect of the coordination environment of surface atoms on the catalytic performance of alloy catalysts, a series of PtxCu1-x alloy model catalysts supported on anatase-phase TiO2 (PtxCu1-x/Ti, x = 0.4, 0.5, 0.6, 0.8) were developed and applied in the classic photocatalytic CO2 reduction reaction. According to the results of catalytic performance evaluation, it was found that the photocatalytic CO2 reduction activity on PtxCu1-x/Ti showed a volcanic change as a function of the Pt/Cu ratio, the highest CO2 conversion was achieved on Pt0.5Cu0.5/Ti, with CH4 as the main product. Further systematic characterizations and theoretical calculations revealed that the equimolar amounts of Pt and Cu in Pt0.5Cu0.5/Ti facilitated the generation of more Cu-Pt-paired sites (i.e., the higher coordination number of Pt-Cu), which would favor a bridge adsorption configuration of CO2 and facilitate the electron transfer, thus resulting in the highest photocatalytic CO2 reduction efficiency on Pt0.5Cu0.5/Ti. This work provided new insights into the design of excellent CO2 reduction photocatalysts with high CH4 selectivity from the perspective of surface coordination environment engineering on alloy catalysts.

High-Volumetric Density Atomic Cobalt on Multishell ZnxCd1-xS Boosts Photocatalytic CO2 Reduction.

The volumetric density of the metal atomic site is decisive to the operating efficiency of the photosynthetic nanoreactor, yet its rational design and synthesis remain a grand challenge. Herein, we report a shell-regulating approach to enhance the volumetric density of Co atomic sites onto/into multishell ZnxCd1-xS for greatly improving CO2 photoreduction activity. We first establish a quantitative relation between the number of shell layers, specific surface areas, and volumetric density of atomic sites on multishell ZnxCd1-xS and conclude a positive relation between photosynthetic performance and the number of shell layers. The triple-shell ZnxCd1-xS-Co1 achieves the highest CO yield rate of 7629.7 μmol g-1 h-1, superior to those of the double-shell ZnxCd1-xS-Co1 (5882.2 μmol g-1 h-1) and single-shell ZnxCd1-xS-Co1 (4724.2 μmol g-1 h-1). Density functional theory calculations suggest that high-density Co atomic sites can promote the mobility of photogenerated electrons and enhance the adsorption of Co(bpy)32+ to increase CO2 activation (CO2 → CO2* → COOH* → CO* → CO) via the S-Co-bpy interaction, thereby enhancing the efficiency of photocatalytic CO2 reduction.

Spin polarization regulates photocatalytic CO2 into hydrocarbons by Co doped BiOCl

Doping magnetic elements into semiconductors is an effective strategy for manipulating spin-polarized electrons in photocatalysis. This work indicates that the introduction of spin-polarized electrons into BiOCl ultrathin sheets remarkably boosts the efficiency of photocatalytic CO2 reduction by doping BiOCl with magnetic Co. The Co-doped BiOCl (Co-BiOCl) photocatalyst selectively converts CO2 into CH4 and C2+ products with a hydrocarbon selectivity of 76.9 %, which is not available for pristine BiOCl. The spin-polarized electrons generated from Co-BiOCl promote CO adsorption, stabilize the key CO* intermediate, and significantly reduce the kinetic barrier to CH2* formation, tuning the subsequent hydrogenation and C−C coupling into hydrocarbons. The regulatory effect of spin polarization on photocatalytic CO2 reduction can also be observed for Fe-, Ni- or non-magnetic element Cu- doped BiOCl. Hence, this work provides new insight into the regulation of the photoreduction of CO2 to hydrocarbon products by spin-polarized electrons.

A P-doped BiOBr nanosheet for enhanced photocatalytic CO2 reduction efficiency

The photocatalytic CO2 reduction efficiency of BiOBr is constrained by its insufficient ability to effectively absorb visible light, as well as its rapid photogenerated electron-hole complexation. Modulating the band gap and charge transfer kinetics of photocatalysts through heteroatom doping is an effective solution. P-doped BiOBr photocatalysts were synthesized through a one-step hydrothermal method to promote the photocatalytic reduction of CO2 in this investigation. The photocatalytic reduction of CO2 to CO using an 8 % P-BiOBr catalyst achieved a rate of 9.13 µmolg−1h−1, which is 3.3 times greater than that observed with the pure BiOBr catalyst. XPS, UV-Vis DRS and Mott-Schottky analyses revealed that P-BiOBr had a narrower forbidden bandwidth and a more negative conduction band, which improved the absorption of visible light and the reduction ability of CO2. Furthermore, The transient photocurrent response, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) spectra signify that the doping of phosphorus (P) enhances the separation and mobility of the carriers generated by light in BiOBr. This research offers a straightforward approach for doping with P, which enhances photocatalytic reduction of CO2 by semiconductor.

Recent Advances in Diverse MXenes‐Based Structures for Photocatalytic CO2 Reduction into Renewable Hydrocarbon Fuels

AbstractPhotocatalytic CO2 reduction into renewable hydrocarbon fuels is a green solution to address CO2 emission and energy issues simultaneously. However, the fast recombination of photogenerated charge carriers and the sluggish surface reaction kinetics restrict the efficiency of photocatalytic CO2 reduction. The emergence of 2D MXenes has potential in improving the efficiency of photocatalytic CO2 reduction, owing to their high electrical conductivity, flexible structural properties, and abundant active sites. Hence, this review will concisely summarize and highlight recent advances of MXenes‐based photocatalysts used in photocatalytic CO2 reduction. First, the synthesis and properties of MXenes is briefly introduced. Second, the mechanism of CO2 photoreduction along with the roles of MXenes in photocatalytic CO2 reduction are summarized, including promoting the adsorption of CO2, enhancing the separation of photo‐induced charge carriers, acting as a robust support, and photothermal effect. Third, different kinds of MXenes‐based photocatalysts such as MXenes/metal oxides, MXenes/nitrides, MXenes/LDH, MXenes/perovskite, and MXene‐derived photocatalysts for CO2 reduction are classified via the type of semiconductors. Finally, the challenges and perspectives are also presented, including exploring suitable MXenes via machine learning, uncovering the structure‐activity relationship by in situ, time‐ and space‐resolved characterization techniques, improving anti‐oxidization ability, and scale‐up applications.

Boosting photocatalytic CO2 reduction efficiency by graphene nanoflakes (GNF) decorated ZIF-67 under visible light irradiation

The design and development of sustainable and cost-effective photocatalysts necessitate significant effort for improved CO2 reduction efficiency. Metal-organic frameworks (MOFs), with high surface area, are gaining popularity in photocatalysis, but their high electron-hole (e-, h+) recombination and low light harvesting capacity limit their utility. Graphene nanoflake (GNF) is a novel, low-cost carbon nanomaterial which has received attention owing to its non-toxicity, high aqueous solubility, unique photoluminescence properties, and excellent photostability. In this work, graphene nanoflake (GNF) decorated zeolitic imidazole framework ZIF-67 (GNF(X)/ZIF-67) has been synthesized for improving visible light-driven photocatalytic CO2 reduction performance. The composite GNF6/ZIF-67 decorated with 6% GNF nanoflake achieves the highest methanol generation of 50.93 µmolg−1 and the highest ethanol generation of 33.97 µmolg−1 after 8 h of visible light irradiation, compared to pure ZIF-67 which is 1.93 and 1.59 times respectively. The effect of GNF on boosting the visible-light photocatalytic activity of ZIF-67 was explored based on the UV-Vis DRS spectra, electrochemical impedance spectra (EIS), transient photocurrent response, and photoluminescence (PL) experiment. This work may discover a new way to synthesize photocatalysts for applying CO2 photoreduction.

Theoretical and experimental investigation of the coordination effect on photocatalytic CO2 reduction efficiency of cobalt single atom catalyst

Visible-light-driven carbon dioxide (CO2) reduction, which converts CO2 into value-added fuels, is an intriguing strategy to simultaneously mitigate the energy crisis and achieve a carbon–neutral economy. Single-atom catalysts (SACs) with homogeneously dispersed definite active sites and adjustable coordination environments show great potential in catalyzing photocatalytic CO2 reduction reaction (CO2RR). According to previously reported studies, the catalytic performance of SACs applied in various fields has a great relationship with their local coordination environment of metal centers. However, in-depth investigation of the coordination effect, which has been widely explored to regulate the electronic structure of SACs, on the activity, selectivity, and stability of CO2 photoreduction has never been reported. Herein, a series of Co single atom photocatalysts with diverse N coordination number (CoSA-Nx/C, x = 2, 3, and 4) were synthesized and their photocatalytic CO2RR performance was examined. Theoretical and experimental investigation demonstrated that the photocatalytic CO2RR activity of Co SACs can be effectively adjusted by fine-regulating the N coordination. The optimal CoSA-N2/C photocatalyst with two-coordinate N atoms with increased unoccupied Co 3d electronic orbitals possesses enhanced CO2 adsorption and activation as well as reduced energy barrier for *COOH intermediate generation, thus showing superior photoconversion of CO2-to-CO performance with 10110 μmol g−1h−1 CO evolution yield, 82.6 % CO selectivity, and long-term stability. This work promotes the future rationally design and synthesis of photocatalysts applied in targeted reactions at atomic scale.

Synthesis of graded Cu-NiO composites and their performance in photocatalytic CO2 reduction of carbon dioxide

Abstract In this paper, firstly, the basic principle and efficiency of photocatalytic CO2 reduction are analyzed, and the thermodynamic and kinetic principles of photoreduction of CO2 are explained. Secondly, the graded Cu-NiO composites were prepared using the solution combustion method, and the atomic structure density properties of the graded Cu-NiO composites were calculated using the Hohenberg-Kohn theorem of density generalization theory. Finally, an empirical analysis was conducted to verify the effectiveness of the graded Cu-NiO composites for photocatalytic CO2 reduction. The results showed that the overall capacitance of Cu-NiO composites was between [−3.5*107F−2·cm2,−1.5*107F−2·cm2], and the methanol yield of 4% Cu-NiO composites reached 729 μmol/g cat and the ethanol yield of 4% Cu-NiO composites decreased to 171 μmol/g cat after 5 h of reaction.

2D/2D combination effects of pBN/gC3N4/TiO2 nanocomposites for photocatalytic CO2 conversion with alternative cationic scavengers

In this study, a series of pBN/gCN and pBN/gCN/TiO2 ternary nanocomposites was successfully fabricated by integrating 2D porous boron nitride and 2D graphitic carbon nitride with TiO2 using different amounts of gCN. First-principles DFT calculations were used for the first time to explore the electronic structure and electron flow in the ternary nanocomposites. The successful junctions of pBN/gCN/TiO2 were determined by analytical techniques, and all the results agreed that pBN, gCN, and TiO2 had interfacial connections with the efficient separation of photogenerated electrons and holes, thereby supplying plentiful photoinduced electrons to CO2R. In the photocatalytic CO2 reduction test, the light source was the principal component of the reactor; thus, we used visible light of different intensities (15 W, 75 W, and 100 W). In NaHCO3 solvent with a TEA electron donor, the CH3OH rates over TBCN2 were 13.79, 15.59, and 14.02 %, respectively. The enhanced efficiency of photocatalytic CO2 reduction is not only explained by the excellent capture of CO2 and the activation performance of TBCN2 with 2D/2D junctions, but also by the rapid charge separation and transfer of photogenerated charge carriers. Hence, this work demonstrates the use of 2D pBN and gCN with TiO2 ternary nanocomposites as novel and efficient catalysts for CO2R.

2D Atomic Layers for CO2 Photoreduction.

Artificial photosynthesis can convert carbon dioxide into high value-added chemicals. However, due to the poor charge separation efficiency and CO2 activation ability, the conversion efficiency of photocatalytic CO2 reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO2 reduction performance. In this review, the basic principle of CO2 photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth-based materials, MXene, metal-organic framework, and metal-free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO2 reduction are prospected.

Amide Covalent Bonding Engineering in Heterojunction for Efficient Solar-Driven CO2 Reduction.

Inefficient charge separation and slow interfacial reaction dynamics significantly hamper the efficiency of photocatalytic CO2 reduction. Herein, a facile EDC/NHS-assisted linking strategy was developed to enhance charge separation in heterojunction photocatalysts. Using this approach, we successfully synthesized amide-bonded carbon quantum dot-g-C3N4 (CQD-CN) heterojunction photocatalysts. The formation of amide covalent bonds between CN and CQDs in the CN-CQD facilitates efficient carrier migration, CO2 adsorption, and activation. Exploiting these advantages, the CN-CQD photocatalysts exhibit high selectivity with CO and CH4 evolution rates of 79.2 and 2.7 μmol g-1 h-1, respectively. These rates are about 1.7 and 3.6 times higher than those of CN@CQD and bulk CN, respectively. Importantly, the CN-CQD photocatalysts demonstrate exceptional stability, even after 12 h of continuous testing. The presence of the COOH* signal is identified as a crucial intermediate species in the conversion of CO2 to CO. This study presents a covalent bonding engineering strategy for developing high-performance heterojunction photocatalysts for efficient solar-driven reduction of CO2.

Graphene Quantum Dots for Photocatalytic CO2 Reduction

Sustainable solar fuels production through reduction of molecular CO2 using photocatalysts is an eco‐friendly and dependable source of energy for the future and for controlling the global warming. The growth of quantum dots, especially, graphene quantum dots (GQD), has emerged as a flat 0D material offering unique properties like enhanced solar light absorption, surface reactivity, charge separation, and migration efficiency, which are invariably systemizing high solar photocatalytic CO2 reduction efficiency. In this review, the insights of thermodynamics and kinetics of CO2 reduction are discussed, followed by detailed encapsulation of modification strategies of GQDs and intrinsic analysis of CO2 reduction utilizing solar light. Progressively, the challenges and futuristic outlook of GQDs‐based photocatalytic systems for solar fuels production is also presented.

One-Step Fabricated Sn0 Particle on S-Vacancies SnS2 to Accelerate Photoelectron Transfer for Sterling Photocatalytic CO2 Reduction in Pure Water Vapor Environment.

Promoting the proton-coupled electron transfer process in order to solve the sluggish carrier migration dynamics is an efficient way to accelerate the photocatalytic CO2 reduction (PCR) process. Herein, through the reduction of Sn4+ by amino and sulfhydryl groups, Sn0 particles are lodged in S-vacancies SnS2 nanosheets. The high conductance of Sn0 particles expedites the collection and transport of photogenerated electrons, activating the surrounding surface of unsaturated sulfur (Sx 2- ) and thus lowering the energy barrier for generation of *COOH. Meanwhile, S-vacancies boost H2 O adsorption while Sx 2- increases CO2 adsorption, as demonstrated by density functional theory (DFT), obtaining a selectivity of 97.88% CO and yield of 295.06 µmol g-1 h-1 without the addition of co-catalysts and sacrificial agents. This work provides a new approach to building a fast electron transfer interface between metal particles and semiconductors, which works in tandem with S-vacancies and Sx 2- to boost the efficiency of photocatalytic CO2 reduction to CO in pure water vapor environment.

Facile synthesis of a Z-scheme CeO2/C3N4 heterojunction with enhanced charge transfer for CO2 photoreduction

Using solar energy to convert CO2 into value-added fuel is crucial for the goal of global carbon neutrality. Effective separation of photogenerated charges is important for improving photocatalytic CO2 reduction efficiency. Herein, we report a facile in situ exfoliation and conversion strategy to synthesize a novel CeO2/C3N4 heterostructure by uniformly distributing CeO2 nanoparticles onto ultrathin porous C3N4 nanosheets. The ultrathin porous structure of C3N4 not only increases the specific surface area to provide more active sites but also effectively shortens the migration distance of photogenerated electron holes to avoid their recombination. In addition, the well-dispersed CeO2 on C3N4 shows an intimate interface contact, which allows more charges to be transferred through the increased interface surface area. The as-synthesized CeO2/C3N4 heterojunction with well-matched band gaps and a Z-scheme structure prolongs the lifetime of photo-induced charge carriers and maximizes the redox ability of the photocatalyst. Without a noble metal cocatalyst or a sacrificial agent, the CO2 photoreduction performance of the CeO2/C3N4 heterojunction is approximately 5-fold enhanced compared with that of bulk C3N4. This study provides a facile strategy for the design and practical application of direct Z-scheme pho-tocatalysts for sustainable energy conversion.

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas-Liquid Interface of Microdroplets.

Solar-driven CO2 reduction reaction (CO2RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO2RR efficiency at the abundant gas-liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO3·0.33H2O mediated by microdroplets reaches 2536 μmol h-1g-1 (vs. 13 μmol h-1g-1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO2RR in bulk phase reaction condition. Beyond the efficient delivery of CO2 to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas-liquid interface of microdroplets essentially promotes the separation of photogenerated electron-hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO2 reduction to fuel.

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas‐Liquid Interface of Microdroplets**

AbstractSolar‐driven CO2 reduction reaction (CO2RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO2RR efficiency at the abundant gas‐liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO3 ⋅ 0.33H2O mediated by microdroplets reaches 2536 μmol h−1 g−1 (vs. 13 μmol h−1 g−1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO2RR in bulk phase reaction condition. Beyond the efficient delivery of CO2 to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas‐liquid interface of microdroplets essentially promotes the separation of photogenerated electron‐hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas‐liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO2 reduction to fuel.

Light Control-Induced Oxygen Vacancy Generation and In Situ Surface Heterojunction Reconstruction for Boosting CO2 Reduction.

The weak adsorption of CO2 and the fast recombination of photogenerated charges harshly restrain the photocatalytic CO2 reduction efficiency. The simultaneous catalyst design with strong CO2 capture ability and fast charge separation efficiency is challenging. Herein, taking advantage of the metastable characteristic of oxygen vacancy, amorphous defect Bi2O2CO3 (named BOvC) was built on the surface of defect-rich BiOBr (named BOvB) through an in situ surface reconstruction progress, in which the CO32- in solution reacted with the generated Bi(3-x)+ around the oxygen vacancies. The in situ formed BOvC is tightly in contact with the BOvB and can prevent the further destruction of the oxygen vacancy sites essential for CO2 adsorption and visible light utilization. Additionally, the superficial BOvC associated with the internal BOvB forms a typical heterojunction promoting the interface carriers' separation. Finally, the in situ formation of BOvC boosted the BOvB and showed better activity in the photocatalytic reduction of CO2 into CO (three times compared to that of pristine BiOBr). This work provides a comprehensive solution for governing defects chemistry and heterojunction design, as well as gives an in-depth understanding of the function of vacancies in CO2 reduction.

Atomic Interface Engineering of Single-Atom Pt/TiO2 -Ti3 C2 for Boosting Photocatalytic CO2 Reduction.

Solar-driven CO2 conversion into valuable fuels is a promising strategy to alleviate the energy and environmental issues. However, inefficient charge separation and transfer greatly limits the photocatalytic CO2 reduction efficiency. Herein, single-atom Pt anchored on 3D hierarchical TiO2 -Ti3 C2 with atomic-scale interface engineering is successfully synthesized through an in situ transformation and photoreduction method. The in situ growth of TiO2 on Ti3 C2 nanosheets can not only provide interfacial driving force for the charge transport, but also create an atomic-level charge transfer channel for directional electron migration. Moreover, the single-atom Pt anchored on TiO2 or Ti3 C2 can effectively capture the photogenerated electrons through the atomic interfacial PtO bond with shortened charge migration distance, and simultaneously serve as active sites for CO2 adsorption and activation. Benefiting from the synergistic effect of the atomic interface engineering of single-atom Pt and interfacial TiOTi, the optimized photocatalyst exhibits excellent CO2 -to-CO conversion activity of 20.5µmol g-1 h-1 with a selectivity of 96%, which is five times that of commercial TiO2 (P25). This work sheds new light on designing ideal atomic-scale interface and single-atom catalysts for efficient solar fuel conversation.

Efficient visible-light-driven CO2 reduction mediated by novel Au-doped BiOBr nanosheets

Photocatalytic reduction of CO2 into valuable resources presents an efficient solution to mitigate the energy crisis and effects of climate change. However, the low efficiency of photocatalytic CO2 reduction of photocatalysts under visible light irradiation limits their industrial applications. Bismuth oxybromide (BiOBr) is a typical visible-light-driven photocatalyst with an appropriate band gap, but the charge separation efficiency still needs to be improved. In this work, the Au-doped BiOBr nanosheets with enhanced electrochemical characteristics were successfully synthesized through a simple one-step hydrothermal procedure. After Au-doping modification, the charge separation efficiency of BOB-Au-I sample were measured as 2.5 times than that of BiOBr nanosheets. And the BOB-Au-I samples exhibited an outstanding photocatalytic capacity for converting CO2 to CO with a yield rate of approximately four times higher than that of BOB nanosheets under visible light irradiation. Furthermore, the mechanism of CO2 reduction was elucidated through in situ Fourier-transform infrared spectroscopy. This study provides a facile method for achieving Au-doping modification of BiOBr nanosheets for efficient reduction of CO2.

Studying the role of dual vacancies over g-C3N4/Zn0.3Cd0.7S for photocatalytic CO2 reduction

Defect engineering as an important surface regulation method, is closely related to the adsorption, activation and transformation of reactant molecules. To improve the efficiency of photocatalytic CO2 reduction from the interfacial perspective, g-C3N4/Zn0.3Cd0.7S (CN/ZCS) heterojunction with dual vacancies were successfully synthesized. The production of CO for the optimal sample (3% CN/ZCS) is significantly improved, about 3.5 times of ZCS and 309.8 times of CN, respectively. Meanwhile, the CO2 adsorption and transformation process are deduced and revealed by monitoring the intermediate and final products on the in-situ FTIR. The underlying enhanced reason can be elucidated by the defective sites and Z-scheme transfer model, which increase the carrier density, active sites and the utilization of photogenerated charge carriers (PCCs). This study provides a new and powerful example in designing novel heterojunction photocatalysts by defect engineering, and helps us to enhance the photocatalytic activity from the interfacial perspective.