Photocatalytic CO2 Reduction Reaction Research Articles

A template co-pyrolysis strategy towards the increase of amino/imino content within g-C3N4 for efficient CO2 photoreduction

Photocatalytic CO2 reduction reaction (CO2RR) is an effective mean to address the current environmental and energy issues. As a kind of typical photocatalyst, g-C3N4 possesses lots of advantages (i.e., facile synthesis, visible-light response, and high stability) in CO2 reduction. However, the poor capacity of CO2 capture and rapid recombination of photo-generated electron and hole, both hinder the further development of g-C3N4 for CO2RR. Herein, we developed a template co-pyrolysis strategy to prepare C–NHx-rich (x = 1 or 2) g-C3N4, to increase the CO2 binding and the subsequent photocatalytic CO2 reduction efficiency. Specifically, organic molecules with multiple imino groups were used as additives to co-pyrolyze with urea. These additives can act as templates to facilitate the formation of g-C3N4 with abundant C–NHx groups, which effectively improved the capacity of CO2 capture. Meanwhile, the capacity of light absorption and the separation of photo-generated electron and hole were also optimized. As a result, the obtained C–NHx-rich g-C3N4 showed greatly enhanced photocatalytic activity for CO2RR, over 74-fold higher than that of g-C3N4 conventionally prepared. This work provides a new avenue for optimizing the g-C3N4-based photocatalysts for CO2RR.

Novel amino-functionalized Ni(II)-based MOFs for efficiently photocatalytic reduction of CO2 to CO with superior selectivity under visible-light illumination

Metal-organic frameworks (MOFs) have aroused ever-growing scientific interest for photocatalytic CO2 reduction reaction (CO2RR). Delicate design and synthesis of MOFs with open metal sites (OMSs) is the key to activate CO2 and even stabilize the reaction intermediates of CO2RR, further determine the superior selectivity. Herein, two amino-functionalized MOFs (Ni-Bpyb and Ni-Bipy) with open Ni(II) sites were constructed from 2′-amino-5′-(4-carboxyphenyl)-[1,1′:3′,1″-terphenyl]-4,4″-dicarboxylic acid (NH2-BTBH3) and different lengths of linear N-donor linkers, 1,4-bis(4-pyridyl) benzene (Bpyb) or 4,4′-bipyridine (Bipy). Under visible-light irradiation, Ni-Bpyb shows more excellent CO yield of 1326.7 μmol·g−1·h−1 with impressive apparent quantum efficiency (AQE, 2.12 %@420 nm) and selectivity (98.80 %). Significantly, this AQE value is at the high end among MOFs-based photocatalysts for CO2RR. The reaction mechanism has been carefully investigated by experimental and theoretical calculations results. Photoelectric experiments demonstrate that Ni-Bpyb shows higher electron–hole separation efficiency compared to Ni-Bipy. Theoretical calculations validate that the open Ni(II) sites of Ni-Bpyb possess lower energy barriers of CO2 adsorption and reducing CO2* to COOH*, as well as better stabilizes COOH* intermediate than those of Ni-Bipy. These merits synergistically contribute to the superior performance and selectivity of Ni-Bpyb. This work might give a guidance for the design of efficient MOFs-based photocatalysts with excellent selectivity for CO2RR.

Three-dimensional palm frondlike Co3O4@NiO/graphitic carbon composite for photocatalytic CO2 reduction

Three-dimensional (3D) palm frondlike S-scheme heterojunction based the Co3O4@NiO/graphitic carbon (Co@Ni/GC) composites were fabricated via a simple polymer heat treatment method as photocatalysts for CO2 reduction reactions (CO2RR). The optimal Co@Ni/GC-700 catalyst exhibits excellent performance and stability for photocatalytic CO2RR. Under visible light irradiation, the maximum yields for CH4 and CO are 9.79 μmol g−1 h−1 and 4.89 μmol g−1 h−1, respectively. The photocatalytic CO2RR activity of the Co@Ni/GC catalysts is superior to Co3O4 or NiO, which could be attributed to the direct S-scheme heterojunction induced by the interfacial electric field (EF) and the improved CO2 adsorption capacity in Co@Ni/GC. DFT calculations revealed that an interfacial EF is formed due to the electron transfer from NiO to Co3O4 in the Co@Ni/GC catalysts. This work provides new insights for designing advanced S-scheme heterojunction photocatalytic CO2RR catalysts with ideal performance.

A Critical Review of the Use of Bismuth Halide Perovskites for CO2 Photoreduction: Stability Challenges and Strategies Implemented

Inspired by natural photosynthesis, the photocatalytic CO2 reduction reaction (CO2RR) stands as a viable strategy for the production of solar fuels to mitigate the high dependence on highly polluting fossil fuels, as well as to decrease the CO2 concentration in the atmosphere. The design of photocatalytic materials is crucial to ensure high efficiency of the CO2RR process. So far, perovskite materials have shown high efficiency and selectivity in CO2RR to generate different solar fuels. Particularly, bismuth halide perovskites have gained much attention due to their higher absorption coefficients, their more efficient charge transfer (compared to oxide perovskites), and their required thermodynamic potential for CO2RR. Moreover, these materials represent a promising alternative to the highly polluting lead halide perovskites. However, despite all the remarkable advantages of bismuth halide perovskites, their use has been limited, owing to instability concerns. As a consequence, recent reports have offered solutions to obtain structures highly stable against oxygen, water, and light, promoting the formation of solar fuels with promising efficiency for CO2RR. Thus, this review analyzes the current state of the art in this field, particularly studies about stability strategies from intrinsic and extrinsic standpoints. Lastly, we discuss the challenges and opportunities in designing stable bismuth halide perovskites, which open new opportunities for scaling up the CO2RR.

N-Heterocyclic Carbene Gold Complexes in a Photocatalytic CO2 Reduction Reaction.

Molecular catalysts that are durable and highly selective in the photocatalytic CO2 reduction reaction (PCO2RR) are in high demand. Molecular gold complexes are underexplored in the CO2RR manifold despite heterogeneous gold-CO2 reduction catalyst counterparts being frequently studied. In this report, a series of N-heterocyclic carbene (NHC)-ligated Au complexes are evaluated in the PCO2RR with an added photosensitizer (tris(2-phenylpyridine)iridium, Ir(ppy)3). The complexes were each studied with and without an added activator used to open a coordination site on the Au complexes. Results show an example of an exceptionally durable PCO2RR catalyst lasting >100 h with high product selectivity for CO. Heterogeneity tests reveal no evidence of a nonhomogeneous active catalyst, and structure-activity relationships of the molecular complexes are discussed.

Z-scheme π-π stacking MXene/GO/PDI composite aerogels to construct interface electron transport network for photocatalytic CO2 reduction

Converting artificial photosynthesis into value-added chemicals through photocatalytic CO2 reduction reaction (CO2RR) is a sustainable and economical strategy to solve energy and environmental problems. Here, a series of new three-dimensional (3D) MXene/GO/perylene diimide (PDI) composite aerogels were prepared, and an electron transfer network in a π-π stacking form was constructed through self-assembly. The methyl formate (MF) generation rate of the optimized MXene/GO/PDI composite aerogel for photocatalytic CO2RR in methanol is 771.1 μmol g−1 h−1, about 8 fold that of the pure MXene/PDI composite catalyst. The substantially improved performance is attributed to the strong coupling heterogeneous interface established by π-π stacked cross-linking network and the Z-scheme heterojunction constructed between MXene/GO aerogel and PDI. Thus, the transmission of photogenerated electrons is accelerated to improve the oxidation-reduction ability at the interface. A tentative mechanism for selective photocatalysis of methanol to MF over MXene/GO/PDI composite aerogels was put forward. This work provides an efficient strategy to prepare non-precious heterostructure photocatalysts for MF production and other related reactions.

A ball milling method for highly dispersed Ni atoms on g-C3N4 to boost CO2 photoreduction

Atomically dispersed active sites can effectively enhance the catalytic activity, but the synthesis of highly dispersed single-atom active sites remains challenging. Herein, we report for the fabrication of single-atom Ni on g-C3N4 (CN) catalysts for photocatalytic CO2 reduction reaction (CO2RR) using a high-energy ball milling method. The uniformly loaded single-atomic Ni on the surface of the substrate suggests the improvement of synthetic methods. After optimizing the Ni loading, the photocatalyst containing 0.5 at% (0.32 wt%) single-atomic Ni (Ni/CN-0.5) exhibited the highest CO2 reduction performance (∼19.9 μmol·g−1·h−1) without any co-catalyst or sacrificial agent. As visualized by aberration-corrected high-angle annular darkfield scanning transmission electron microscopy (AC HAADF-STEM), the Ni atoms in the Ni/CN-0.5 photocatalyst are most uniformly dispersed for different loadings (0.1, 0.3, 0.5, 0.7, 1.0, 3.0 and 5.0 at%). These results suggest that the uniformity of the single-atom active sites plays a decisive role rather than the loading amount in the highly enhanced performance. This work provides insight into the design of photocatalysts with highly dispersed single-atom catalytic active sites for enhancing activity.

General strategy for enhanced CH4 selectivity in photocatalytic CO2 reduction reactions by surface oxophilicity engineering

Rationally designing and controlling the interactions between reaction intermediates and the surface of photocatalysts is critical to obtain high product selectivity in photocatalysis. Herein, using CdS-based photocatalytic CO2 reduction reaction (CO2RR) as a model system, we demonstrate that CH4 selectivity can be significantly enhanced through the introduction of La3+ ions with high oxophilicity on the surface of the photocatalysts. The high surface oxophilicity of the photocatalysts can increase CO* desorption energy and promote further hydrogenation to CH4. In contrast, when Au3+ ions with low oxophilicity were doped in CdS, reduced CH4 selectivity was observed in the CO2RR. Significantly, enhanced CH4 selectivity can be achieved by doping oxophilic La3+ ions into a broad range of alternative photocatalysts including ZnO, SnS2, BiOBr, BiVO4, TaON, and CsPbBr3, which demonstrates the general strategy to enhance CH4 selectivity of photocatalytic CO2RR through increased surface oxophilicity of the photocatalysts by rare earth La3+ ion doping.

Carbon Dots Mediated In Situ Confined Growth of Bi Clusters on g-C3 N4 Nanomeshes for Boosting Plasma-Assisted Photoreduction of CO2.

Synthesis of high-efficiency, cost-effective, and stable photocatalysts has long been a priority for sustainable photocatalytic CO2 reduction reactions (CRR), given its importance in achieving carbon neutrality goals under the new development philosophy. Fundamentally, the sluggish interface charge transportation and poor selectivity of products remain a challenge in the CRR progress. Herein, this work unveils a synergistic effect between high-density monodispersed Bi/carbon dots (CDs) and ultrathin graphite phase carbon nitride (g-C3 N4 ) nanomeshes for plasma-assisted photocatalytic CRR. The optimal g-C3 N4 /Bi/CDs heterojunction displays a high selectivity of 98% for CO production with a yield up to 22.7 µmol g-1 without any sacrificial agent. The in situ confined growth of plasmonic Bi clusters favors the production of more hot carriers and improves the conductivity of g-C3 N4 . Meanwhile, a built-in electric field driving force modulates the directional injection photogenerated holes from plasmonic Bi clusters and g-C3 N4 photosensitive units to adjacent CDs reservoirs, thus promoting the rapid separation and oriented transfer in the CRR process. This work sheds light on the mechanism of plasma-assisted photocatalytic CRR and provides a pathway for designing highly efficient plasma-involved photocatalysts.

Construction of the charge transfer channels for enhanced photocatalytic CO2 reduction reaction

Core-shell TiO2@g-C3N4 (TCN) photocatalysts with Pd channels (TPCN) were successfully fabricated, which improve the separation efficiency of electrons and holes. Intercalated Pd single atoms become channels to guide the electrons transfer in a specific direction, which facilitate the transport of the electrons. TPCN catalysts exhibit an excellent photocatalytic performance to reduce CO2 into CH4 because the energy to form CO is higher than that of CH4. Importantly, the selectivity for CH4 is also greatly improved and the yield of CH4 increases nearly 5.9 times than TCN. The concept of constructing charge transfer channels is expected to provide new implications for the synthesis of photocatalysts.

Design and application of g-C3N4-based materials for fuels photosynthesis from CO2 or H2O based on reaction pathway insights

Photocatalytic CO2 reduction reaction (CRR) and hydrogen evolution reaction (HER) based on graphitic carbon nitride (g-C3N4) that is regarded as the metal-free “holy grail” photocatalyst, provide promising strategies for producing next-generation fuels, contributing to achieving carbon neutrality, alleviating energy and environment crisis. However, the activity of CRR and HER over g-C3N4 leaves much to be desired. Therefore, numerous studies have sprung up to enhance photoactivity. A comprehensive understanding of the CRR and HER reaction pathways is crucial for designing g-C3N4-based materials, further promoting efficient fuel production. Different from previous reviews that focus on g-C3N4 modification from the viewpoint of material science. In this review, we divided the multistep processes of CRR and HER into five reaction pathways and summarized the latest advances for improving each pathway of fuels synthesis through CRR or HER. Meanwhile, the existing bottleneck issues of each step were also discussed. Finally, comprehensive conclusions, including the remaining challenges, outlooks, etc., for CRR and HER over g-C3N4 were put forward. We are sure that this review will conduce to the understanding of the structure–activity relationship between CRR, HER processes, and g-C3N4 structure, which can provide the reference for developing high-powered photocatalysts, not confined to g-C3N4.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction

The photocatalytic CO2 reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In2O3 plasmonic photocatalysts. The Ag–In2O3 compounds show remarkedly enhanced photocatalytic activity for CO2 conversion to CO compared to pristine In2O3. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag–In2O3-10 is 1.56 μmol/g/h, achieving 5.38-folds higher than that of In2O3 (0.29 μmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In2O3 on Ag–In2O3 compounds. In Ag–In2O3 compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In2O3, resulting in the photocatalytic activity enhancement of Ag–In2O3 compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Efficient CO2 reduction to reveal the piezocatalytic mechanism: From displacement current to active sites

Piezocatalysis has attracted the increasing interest of researchers as a novel catalytic method. To date, there are two popular mechanisms regarding the piezocatalysis, i.e., the piezoelectric effect and the energy band theory. However, both mechanisms cannot fully explain the piezocatalytic process: the electrons generated by the piezoelectric effect will not spontaneously participate in the piezocatalysis, while not all piezoelectric materials have an appropriate energy band structure. In this work, displacement current and the principle of piezoelectric nanogenerator are introduced to fully comprehend the piezocatalytic mechanism for the first time. As a proof-of-concept catalytic system, we synthesize Co-N-C@BaTiO3 piezocatalyst for the CO2 reduction reaction (CO2RR) under ultrasonic vibration. A promising piezocatalytic CO2 reduction rate of 261.8 mol g−1h−1 is achieved with a high CO selectivity up to 93.8% under 50 kHz ultrasonic vibration. The CO yields of this catalytic system outperform most of the reported photocatalytic CO2RR and piezocatalytic CO2RR. Moreover, a comprehensive piezocatalytic mechanism from displacement current to active sites is proposed and supported by combining Co-N-C@BaTiO3 piezoelectric nanogenerator, COMSOL simulation and energy band structure analysis. Under the ultrasonic vibration, the electrons generated by the piezoelectric effect are driven by the time-varying electrostatic potential formed by the displacement current. The suitable band structure of piezoelectric provider that satisfies the potential of reaction promotes electrons to participate in CO2RR on active sites. Overall, our work provides an insightful understanding of piezocatalysis and paves a new path for its development.

VO4 -Modified Layered Double Hydroxides Nanosheets for Highly Selective Photocatalytic CO2 Reduction to C1 Products.

The conversion of CO2 into high-value added chemicals driven by solar energy is an effective way to solve environmental problems, which is, however, largely restricted by the competition reaction of the hydrogen evolution reaction (HER) and easy electron-hole recombination, etc. Herein, VO4 -supported ultrathin NiMgV-layered double hydroxide (V/NiMgV-LDH) nanosheets are successfully fabricated, and the extended X-ray absorption fine structure (EXAFS) and density function theory (DFT) calculations reveal that VO4 species are located on the top of V atoms in the NiMgV-LDH laminate. The V/NiMgV-LDH is proved to be highly efficient for the photocatalytic CO2 reduction reaction (CO2 PR) with high selectivity of 99% for C1 products and nearly no HER (<1%) takes place under visible light. Contrast experiments using NiMgV-LDH as the catalyst for CO2 PR show a CO selectivity of 71.40% and a H2 selectivity of 28.11%. Such excellent performance of V/NiMgV-LDH can be attributed to the following reasons: 1) the V/NiMgV-LDH modulates the band structure and promotes the separation of electrons and holes; 2) strong bonding between V/NiMgV-LDH and CO* and H* facilitates the hydrogenation to form CH4 and inhibits the formation of by-product H2 at the same time.

Perovskite-Nanoparticle-Incorporated NH2-MIL-125(Ti) Nanoreactors with an Optimal Conduction Band Offset for Visible-Light-Driven CO2 Reduction

To alleviate the intense global warming crisis, developing high-performance photocatalysts for CO2 reduction reaction (CO2RR) to green fuels is of great importance. CsPbBr3 (CPB) has been proved as a promising photocatalyst for CO2RR due to the excellent visible-light response and energetic reduction potential, but its practical performance is still deficient, suffering from severe carrier recombination and poor CO2 adsorption capability. Herein, we demonstrate novel CPB-nanocrystal-incorporated NH2-MIL-125(Ti) (NH2-MIL-125(Ti)/CPB) nanoreactors for solar-driven CO2RR. Attributed to the optimal conduction band offset (CBO) in the NH2-MIL-125(Ti)/CPB heterojunction, excellent carrier transfer is obtained with retained energetic photoreduction potential. Moreover, strong interfacial interaction is demonstrated, enabling the synergistic effect of promoted CO2 adsorption on NH2-MIL-125(Ti) and facilitating interfacial carrier injection. Therefore, greatly enhanced photocatalytic CO2RR performance is achieved by as-designed nanoreactors. This work offers a deep understanding into the synthesis of functionalized perovskite-based materials with rationally designed carrier transfer behaviors for not only photocatalytic reactions but also photovoltaic fields.

Ferrocene-boosting Zr-MOFs for efficient photocatalytic CO2 reduction: A trade-off between enhancing LMCT and frustrating Lewis acid

The introduction of rich-electron ligands is a promising strategy to improve the ligand-to-metal charge transfer (LMCT) ability of metal–organic frameworks (MOFs) for efficient photocatalytic CO2 reduction reactions (CO2RR), while the resulting impaired Lewis acid sites go against stable bonding with CO2 and hinder the electron transfering to CO2. It is thus the key to search a trade-off between increasing LMCT and frustrating Lewis acid. Herein, the ferrocene (Fc) modified UiO-66 series MOFs, NH2-UiO-66-Fc, have been prepared to optimize LMCT for boosting CO2RR through a simple solvent-assisted ligand incorporation (SALI) method. Theoretical calculation and systematic experiments, including photoelectrochemical measures, in situ electron paramagnetic resonance, fluorescence probe analysis and X-ray photoelectron spectroscopy indicate that with increasing Fc content, the LMCT energy of MOFs significantly decreases from 2.66 to 2.10 eV based on the established electron transfer double-channel mechanism, while the Lewis acidity of Zr sites reduces with the CO2 adsorption energy (Ead) ranging from −1.061 to −0.632 eV. Through introducing an optimal Fc content, NH2-UiO-66-Fc(2.0) integrating satisfactory LMCT ability and Lewis acidity shows superior photocatalytic CO2RR performance (CO yield: 90.65 μmol·g−1·h−1), about 13 times higher than that of the unmodified MOF and superior to most reported pristine MOF photocatalysts. DFT calculation demonstrates that the excellent performance of NH2-UiO-66-Fc(2.0) is attributed to the lowest energy barrier of 1.50 eV for the rate-limiting step of *COOH formation. In this work, such a simple post-modification strategy for facilitating the whole electron transfer path of photocatalytic CO2RR will provide a new way to construct high-performance MOFs-based CO2RR photocatalysts.

Spin-Polarized Photocatalytic CO2 Reduction of Mn-Doped Perovskite Nanoplates.

"Spin" has been recently reported as an important degree of electronic freedom to improve the performance of electrocatalysts and photocatalysts. This work demonstrates the manipulations of spin-polarized electrons in CsPbBr3 halide perovskite nanoplates (NPLs) to boost the photocatalytic CO2 reduction reaction (CO2RR) efficiencies by doping manganese cations (Mn2+) and applying an external magnetic field. Mn-doped CsPbBr3 (Mn-CsPbBr3) NPLs exhibit an outstanding photocatalytic CO2RR compared to pristine CsPbBr3 NPLs due to creating spin-polarized electrons after Mn doping. Notably, the photocatalytic CO2RR of Mn-CsPbBr3 NPLs is significantly enhanced by applying an external magnetic field. Mn-CsPbBr3 NPLs exhibit 5.7 times improved performance of photocatalytic CO2RR under a magnetic field of 300 mT with a permanent magnet compared to pristine CsPbBr3 NPLs. The corresponding mechanism is systematically investigated by magnetic circular dichroism spectroscopy, ultrafast transient absorption spectroscopy, and density functional theory simulation. The origin of enhanced photocatalytic CO2RR efficiencies of Mn-CsPbBr3 NPLs is due to the increased number of spin-polarized photoexcited carriers by synergistic doping of the magnetic elements and applying a magnetic field, resulting in prolonged carrier lifetime and suppressed charge recombination. Our result shows that manipulating spin-polarized electrons in photocatalytic semiconductors provides an effective strategy to boost photocatalytic CO2RR efficiencies.

Advances and challenges in developing cocatalysts for photocatalytic conversion of carbon dioxide to fuels

The global adoption of efficient sustainable energy sources is a crucial step toward meeting energy demands while achieving carbon emission reduction targets. Solar energy has become a clean and cost-competitive alternative to traditional fossil fuels, but the intermittent nature of sunlight results in challenges associated with energy storage and transport. Photocatalytic carbon dioxide reduction intends to mimic natural photosynthesis for utilizing sunlight to chemically convert water and CO2 into fuels. In this process, the solar energy is captured and stored in fuels, so-called solar fuels, for widespread on-demand use. Heterogeneous solar fuel production systems are multi-component, comprising light-harvesting (photosensitizer) and catalytic (cocatalyst) units. Cocatalysts are indispensable for photocatalytic CO2 reduction systems, which promote charge carrier separation and transport, reduce the reaction activation energy, and alter the reaction route, thereby enhancing the activity and selectivity of the photocatalytic reactions. This review presents a comprehensive summary of the recent advancements in cocatalysts for photocatalytic CO2 reduction reaction (CO2RR), with the purpose of providing new insights and guidance to the field with regard to research directions and best practices. We summarize how various cocatalysts including inorganic nanoparticles, metal complexes, enzymes, and bacteria can be combined with semiconductor photosensitizer for light-driven photocatalytic CO2RR. Side-by-side comparisons reveal the strengths and limitations of each kind of cocatalysts and how lessons extracted from studying natural photosynthetic systems can be applied to investigations of artificial photosynthesis, presenting an outlook discussing possible future concepts for a more effective photocatalytic CO2 reduction process.

Cost-Effective 2D Ultrathin Metal-Organic Layers with Bis-Metallic Catalytic Sites for Visible Light-Driven Photocatalytic CO2 Reduction.

As novel generated 2D materials, metal-organic layers (MOLs) have recently emerged as a potential platform for photocatalytic CO2 reduction reaction (PCO2 RR). Such 2D structures negate the blemish of low-density catalytic sites and low electron transmission efficiency on the surface of metal organic frameworks (MOFs), while retaining the advantage of low expenditure when using earth-abundant metal nodes and meritorious applicability in the PCO2 RR. Herein, it is reported that the 2D ultrathin layer material with bis-metallic catalytic sites (Ni-O metal node and the Ni-N metal site) from bidentate ligand 2,2'-bipyridine-5,5'-dicarboxylate (H2 bpydc) and nickel(II) remarkably boosts the visible light-driven PCO2 RR performance with a CO yield of 2400 mmol g-1 for 18 h and a selectivity up to 99 %. Consequently, the effects of morphology, catalytic sites and intrinsic properties on PCO2 RR efficiency have been investigated in detail. In this context, the ultrathin layer structure has been elucidated as the key point to facilitate electron transfer efficiency. Notably, the bis-metallic catalytic sites with reasonable distance between two adjacent metals presumably induce synergistic effect and offer a guiding ideology for further designing high performance photocatalysts.

Unraveling photocatalytic electron transfer mechanism in polyoxometalate-encapsulated metal-organic frameworks for high-efficient CO2 reduction reaction

Unraveling the fundamental electron transfer mechanism is vital to deeply understand the heterogeneous photocatalysis process so as to develop new efficient photocatalysts. Herein, we present a deep investigation on the electron-transfer mechanism in heterogeneous photocatalytic CO2 reduction reaction by adopting a new type of structurally clear polyoxometalate-encapsulated metal-organic frameworks {Hn[Cd6L6Cl7]4[POM]8} (L=1,4-di(4H-1,2,4-triazol-4-yl)benzene, POM={SiW12}, {PW12} and {PMo12}, abbr.POM@CdMOF) as model photocatalysts. Transient photovoltage measurements indicate that various POM guests in photoactive CdMOF hosts show different electron transfer behaviors and charge separation pathways, inducing different photocatalytic activities. Thereinto, SiW12@CdMOF and PW12@CdMOF exhibit high photocatalytic CO2 reduction activities with CO yields of 4.35 mmolCO·molCd−1·h−1 and 3.60 mmolCO·molCd−1·h−1 comparably to most reported photocatalysts, whereas the performance of PMo12@CdMOF is poor. The in-situ transient photovoltage and DFT calculations revealed the key regulation role of different POM units on the interfacial electron transfer and the adsorption behavior of the important intermediates, thus describing a feasible route to efficiently perform the photocatalytic CO2 reduction. This work may provide a new and significant guideline for exploring high-performance photocatalysts.