Selective Photocatalytic CO2 Reduction Research Articles

Fabrication of a Partial Encapsulation Architecture on S-Scheme Heterojunctions toward Durable Selective Photocatalytic CO2 Reduction.

It remains a challenging issue to achieve durably stable photocatalytic CO2 reduction over heterojunctions owing to their inherent structural assembly features. Herein, a unique partial encapsulation architecture is fabricated on the 3D/2D CoWO4/C3N5 heterojunction by embedding CoWO4 microspheres on C3N5 nanosheets, which achieves efficient, durable, stable, and selective photocatalytic CO2 reduction. For the optimal 5%-CoWO4/C3N5 heterojunction, the yield of selective CO2 reduction to CO is 7.70 and 3.82 times higher than those of CoWO4 and C3N5 in 4 h, respectively, and it maintains a stable CO generation rate within 20 cycles over 80 h. A series of characterization experiments and density functional theory calculations reveal that the structural stability is reinforced significantly via strong interfacial interaction owing to the unique partial encapsulation architecture fabricated on the 3D/2D CoWO4/C3N5 heterojunction, the separation efficiency of photogenerated carriers is improved by inducing a built-in electric field and triggering the S-scheme charge-transport path, and the high CO product selectivity is attributed to the much lower free energy required for the generation path of CO compared to that for CH4.

In-situ construction of Bi-MOF-derived S-scheme BiOBr/CdIn2S4 heterojunction with rich oxygen vacancy for selective photocatalytic CO2 reduction using water

In this study, a highly selective MOF-BiOBr/CdIn2S4 (MOF-BiOBr/CIS) heterostructure with CdIn2S4 nanosheets grown in situ on the tubular structure derived from Bi-MOF-based BiOBr was successfully constructed using a hydrothermal method. Under simulated solar light without sacrificial or photosensitizing agents, the 20-MOF-BiOBr/CIS composite exhibited excellent photocatalytic CO2 performance, achieving production rates of 30.18 μmol‧g−1‧h−1 for CO and 1.50 μmol‧g−1‧h−1 for CH4. Compared to pure MOF-BiOBr and CdIn2S4, the CO production rates were increased by approximately 9 and 116 times, respectively. It was revealed that the 20-MOF-BiOBr/CIS composite with rich oxygen vacancy exhibited close interfacial contact and efficient charge transfer. The formation of MOF-BiOBr/CdIn2S4 heterojunction thereby provided efficient CO2 photocatalytic reduction. The CO selectivity of 20-MOF-BiOBr/CIS reached 83.4 %, and the MOF-BiOBr/CIS heterojunction exhibited good stability over multiple cycles. Furthermore, a mechanism for enhanced photocatalytic CO2 reduction by the MOF-BiOBr/CIS heterojunction was also proposed.

M/BiOCl-(M=Pt, Pd, and Au) Boosted Selective Photocatalytic CO2 Reduction to C2 Hydrocarbons via *CHO Intermediate Manipulation.

Selective CO2 photoreduction to C2 hydrocarbons is significant but limited by the inadequate adsorption strength of the reaction intermediates and low efficiency of proton transfer. Herein, an ameliorative *CO adsorption and H2O activation strategy is realized via decorating bismuth oxychloride (BiOCl) nanostructures with different metal (Pt, Pd, and Au) species. Experimental and theoretical calculation results reveal that distinct *CO binding energies and *H acquisition abilities of the metal cocatalysts mediate the CO2 reduction activity and hydrocarbon selectivity. The relatively moderate *CO adsorption and *H supply over Pd/BiOCl endows it with the lowest free energy to generate *CHO, leading to its highest activity of hydrocarbon production. Specifically, the Pt cocatalyst can efficiently participate in H2O dissociation to deliver more *H for facilitating the protonation of the *CHO and *CHOH, thereby favoring CH4 production with 76.51% selectivity. A lower *H supply over Pd/BiOCl and Au/BiOCl results in a large energy barrier for *CHO or *CHOH protonation and thus a more thermodynamically favored OC─CHO coupling pathway, which endows them with vastly increased C2 hydrocarbon selectivity of 81.21% and 92.81%, respectively. The understanding of efficient C2 hydrocarbon production in this study sheds light on how materials can be engineered for photocatalytic CO2 reduction.

Highly selective photocatalytic CO2 reduction into C2H4 enabled by metal–organic framework-derived catalysts with high Cu+ content

The highly selective conversion of CO2 into valuable C2H4 is a highly important but particularly challenging reaction. Herein, the metal–organic frameworks MOF-74(Cu) with infinite Cu(II)-O chains and Cu-BTC (BTC=benzene-1,3,5-tricarboxylate) with paddle-wheel binuclear Cu(II) clusters are used as precursors. These MOFs are reduced by NaBH4 to obtain Cu0/Cuδ+-based photocatalysts denoted as R-MOF-74(Cu) and R-Cu-BTC, respectively. Significantly, R-MOF-74(Cu) achieves a high selectivity of 90.2 % for C2H4 with a yield rate of 6.5 μmol g−1 within 5 h due to its high Cu+ content. To the best of our knowledge, this C2H4 product selectivity is a record high among all the photocatalysts reported so far for photocatalytic CO2 reduction. In contrast, R-Cu-BTC only forms CO as a product with a cumulative yield of 0.7 μmol g−1 within 5 h. Photoelectrochemical characterization and electron paramagnetic resonance results show that R-MOF-74(Cu) has low interfacial transfer resistance, high photogenerated electron separation efficiency, and excellent CO2 activation and water oxidation performance. In addition, in situ Fourier transform infrared spectroscopy is used to determine the possible reaction pathway from CO2 to C2H4 over R-MOF-74(Cu). This work demonstrates the great potential of MOF-derived photocatalysts for the conversion of CO2 into C2H4 and provides guidance for future photocatalyst development.

Regulating Local Electron Density of Cyano Sites in Graphitic Nitride Carbon by Giant Internal Electric Field for Efficient CO2 Photoreduction to Hydrocarbons.

Selective photocatalytic CO2 reduction to high-value hydrocarbons using graphitic carbon nitride (g-C3N4) polymer holds great practical significance. Herein, the cyano-functionalized g-C3N4 (CN-g-C3N4) with a high local electron density site is successfully constructed for selective CO2 photoreduction to CH4 and C2H4. Wherein the potent electron-withdrawing cyano group induces a giant internal electric field in CN-g-C3N4, significantly boosting the directional migration of photogenerated electrons and concentrating them nearby. Thereby, a high local electron density site around its cyano group is created. Moreover, this structure can also effectively promote the adsorption and activation of CO2 while firmly anchoring *CO intermediates, facilitating their subsequent hydrogenation and coupling reactions. Consequently, using H2O as a reducing agent, CN-g-C3N4 achieves efficient and selective photocatalytic CO2 reduction to CH4 and C2H4 activity, with maximum rates of 6.64 and 1.35µmol g-1h-1, respectively, 69.3 and 53.8 times higher than bulk g-C3N4 and g-C3N4 nanosheets. In short, this work illustrates the importance of constructing a reduction site with high local electron density for efficient and selective CO2 photoreduction to hydrocarbons.

Structure-Function Relationship of p-Block Bismuth for Selective Photocatalytic CO2 Reduction.

Selective photocatalytic reduction of CO2 to value-added fuels, such as CH4, is highly desirable due to its high mass-energy density. Nevertheless, achieving selective CH4 with higher production yield on p-block materials is hindered by non-ideal adsorption of *CHO key intermediate and an unclear structure-function relationship. Herein, we unlock the key reaction steps of CO2 and found a volcano-type structure-function relationship for photocatalytic CO2-to-CH4 conversion by gradual reduction of the p-band center of the p-block Bi element leading to formation of Bi-oxygen vacancy heterosites. The selectivity of CH4 is also positive correlation with adsorption energy of *CHO. The Bi-oxygen vacancy heterosites with an appropriate filled Bi-6p orbital electrons and p band center (-0.64) enhance the coupling between C-2p of *CHO and Bi-6p orbitals, thereby resulting in high selectivity (95.2 %) and productivity (17.4 μmol g-1 h-1) towards CH4. Further studies indicate that the synergistic effect between Bi-oxygen vacancy heterosites reduces Gibbs free energy for *CO-*CHO process, activates the C-H and C=O bonds of *CHO, and facilitates the enrichment of photoexcited electrons at active sites for multielectron photocatalytic CO2-to-CH4 conversion. This work provides a new perspective on developing p-block elements for selective photocatalytic CO2 conversion.

Rich Sulfur Vacancies and Reduced Schottky Barrier Height Synergistically Enable Au/ZnIn2S4 with Enhanced Photocatalytic CO2 Reduction into CO.

Constructing the plasmonic metal/semiconductor heterostructure with a suitable Schottky barrier height (SBH) and the sufficiently reliable active sites is of importance to achieve highly efficient and selective photocatalytic CO2 reduction into hydrocarbon fuels. Herein, we report Au/sulfur vacancy-rich ZnIn2S4 (Au/VSR-ZIS) hierarchical photocatalysts, fabricated via in situ photodepositing Au nanoparticles (NPs) onto the nanosheet self-assembled ZnIn2S4 (ZIS) micrometer flowers (MFs) with rich sulfur vacancies (VS). Density functional theory (DFT) calculations confirm that for the Au/VSR-ZIS system, the Au NPs serve as the reaction sites for H2O oxidation, and the VSR-ZIS MFs serve as those for CO2 reduction. The rich VS in the Au/VSR-ZIS hybrid can reduce its SBH so as to boost more hot electrons in the Au NPs across its Schottky barrier and then inject into the conduction band (CB) of the VSR-ZIS MFs. In addition, VS can also act as the electron sink to trap the photogenerated electrons, retarding the recombination of photogenerated carriers. The two merits effectively enhance the photogenerated electron density in the surface of VSR-ZIS MFs, availing CO2 photoreduction. In addition, the introduction of rich VS in the Au/VSR-ZIS hybrid can offer more active sites, benefiting the CO2 adsorption and accelerating the desorption of CO* from the surface of the photocatalyst. Therefore, under visible light illumination with no sacrificial reagent, the optimum photocatalyst (Au/VSR-ZIS-0.4) presents the enhanced and selective CO2 photoreduction into CO (8.15 μmol g-1h-1 and near 100%), which are superior to those of most of ZIS-based and plasmon-based photocatalysts. The photocatalytic activity is about 40.0-fold as high as that of the Vs-poor-ZIS (VSP-ZIS) MFs. This work contributes a viable strategy for designing highly efficient plasmonic photocatalysts by using the synergism of the anion vacancies and the optimized SBH induced by them.

Rational design of spatial charge separation and targeted active site Cu for highly selective photocatalytic CO2 reduction to CH4

Photocatalytic CO2 reduction reaction (CO2RR) is usually constrained by sluggish kinetics and low product selectivity. Herein, a Cu-doping multi-tier hierarchical S-scheme heterostructure Cu-ZnIn2S4/ZIF-67 was fabricated, achieving highly efficient photocatalytic CO2RR under visible light without additional thermal input. At low pressure (absolute pressure 40 kPa), the optimized catalyst 2Cu-ZISF demonstrated a CH4 yield of 22.27 μmol g−1h−1 with a selectivity of 94.7 %. In situ XPS and EPR confirmed that the photogenerated charge transfer obeys an S-scheme mechanism, with Cu sites serving as electron-rich centers, facilitating spatial charge separation. In situ DRIFT detected reaction intermediates of photocatalytic CO2RR mechanism, and Gibbs free energy calculations via Density Functional Theory revealed that Cu incorporation significantly stabilizes surface CO* species, thus reducing CO(g) production and facilitating hydrogenation, thereby acting as targeted active sites for CH4 production. This work overcomes the limitations of slow reaction kinetics and offers an in-depth understanding of how to design effective S-scheme heterojunction photocatalysts and their charge transfer mechanisms.

Internal electric field-modulated dual S-scheme ZnO@Co3O4/CsPbBr3 nanocages for highly active and selective photocatalytic CO2 reduction

The rational design of a step-scheme (S-scheme) heterojunction with strong internal electric field (IEF) and high redox capacity is a promising strategy for photocatalytic CO2 reduction reaction (CO2RR). However, the precise process of charge transport on the multi-interfaces remains a great challenge. Herein, a dual S-scheme heterojunction constructed in the ZnO@Co3O4/CsPbBr3 hierarchical nanocage was prepared for enhancing CO2RR activity. Without sacrificial agent and photosensitizer, the optimal photocatalyst exhibits a competitive CH4 yield rate of 238.8 μmol g−1h−1 with high selectivity (90.9%), affording an apparent quantum efficiency of 4.6 % at 400 nm, outperforming most previously comparable photocatalysts. In situ X-ray photoelectron spectroscopy (in situ XPS), photoelectrochemical measurement and theoretical calculation verifies the dual S-schematic charge-transport pathway. The remarkably improved performance in CO2RR is due to the rapid charge separation through O-Co-Br bridge driven by the strong internal electric field. This research furnishes a new insight to reveal dynamic charge transfer mechanism for CO2 conversion applications.

A bifunctional catalyst derived from copper metal−organic framework for highly selective photocatalytic CO2 reduction and CO2 cycloaddition reaction

Highly efficient conversion of CO2 into valuable chemicals using green chemical reactions is attractive to the alleviation of global warming. Developing active catalysts with high selectivity remains challenging and is still in pursuit. Herein, a Cu-based metal−organic framework was successfully synthesized by a facile method and denoted as CuTIA. The obtained CuTIA with rich Lewis acid/base sites exhibited enhanced CO2 affinity and served as a bifunctional catalyst for CO2 conversion. To be specific, CuTIA converted CO2 into CH4 (103.78 μmol g−1 h−1) with a selectivity of 100 % under visible light irradiation. Besides, CuTIA drove CO2 cycloaddition reaction with epoxides to produce cyclic carbonates with a yield almost 100 % under mild conditions. This study provides a new perspective in the fabrication of bifunctional catalysts for enhancing CO2 conversion.

Asymmetric Cu(I)─W Dual-Atomic Sites Enable C─C Coupling for Selective Photocatalytic CO2 Reduction to C2H4.

Solar-driven CO2 reduction into value-added C2+ chemical fuels, such as C2H4, is promising in meeting the carbon-neutral future, yet the performance is usually hindered by the high energy barrier of the C─C coupling process. Here, an efficient and stabilized Cu(I) single atoms-modified W18O49 nanowires (Cu1/W18O49) photocatalyst with asymmetric Cu─W dual sites is reported for selective photocatalytic CO2 reduction to C2H4. The interconversion between W(V) and W(VI) in W18O49 ensures the stability of Cu(I) during the photocatalytic process. Under light irradiation, the optimal Cu1/W18O49 (3.6-Cu1/W18O49) catalyst exhibits concurrent high activity and selectivity toward C2H4 production, reaching a corresponding yield rate of 4.9µmol g-1 h-1 and selectivity as high as 72.8%, respectively. Combined in situ spectroscopies and computational calculations reveal that Cu(I) single atoms stabilize the *CO intermediate, and the asymmetric Cu─W dual sites effectively reduce the energy barrier for the C─C coupling of two neighboring CO intermediates, enabling the highly selective C2H4 generation from CO2 photoreduction. This work demonstrates leveraging stabilized atomically-dispersed Cu(I) in asymmetric dual-sites for selective CO2-to-C2H4 conversion and can provide new insight into photocatalytic CO2 reduction to other targeted C2+ products through rational construction of active sites for C─C coupling.

Enhanced selective photocatalytic CO2 reduction to CO on AuPd decorated Bi2O2.33 nanosheets

Photocatalytic conversion of carbon dioxide (CO2) into valuable fuels addresses pressing needs for renewable energy and carbon neutrality. However, conventional photocatalytic CO2 reduction on semiconductor is usually limited by sluggish electron kinetics, poor efficiency and low product selectivity. Herein, we developed a bimetallic Au/Pd-decorated Bi2O2.33 ultrathin nanosheet photocatalyst for highly selective CO2 reduction to CO under visible light irradiation. Bi2O2.33 nanosheets self-assembled from nanodots serve as ideal supports for Au/Pd anchoring due to abundant grain boundaries. Systematic characterization reveals the formation of alloyed Au/Pd nanoparticles on the Bi2O2.33 surface, which endowed a superior CO production rate of 436.8 μmol g−1 h−1 with a selectivity of 96.68 % from CO2 photoreduction. Quantum chemical calculations uncover that plasmonic Au/Pd alloys facilitates interfacial charge transfer and CO2 activation to form the CO-yielding intermediate. This work demonstrates an effective strategy for designing bimetallic plasmonic cocatalysts to optimize the photoreduction selectivity and efficiency of semiconductor photocatalysts.

Metal–oxygen hybridization in Agcluster/TiO2 for selective CO2 photoreduction to CH4

Selective photocatalytic reduction of CO2 to CH4 is one of the most efficient ways to achieve carbon neutralization. However, the formation of methane remains a challenge due to the slow multiple-proton-coupled electron transfer process and the involvement of various C1 intermediates. Herein, an Agcluster/TiO2 catalyst with Ag-O hybridization was synthesized by supporting Ag clusters on anatase phase TiO2 microspheres for photocatalytic CO2 methanation. The Agcluster/TiO2 sample presents an electron selectivity of 86 % for CH4 production with a yield of 25.25 μmol g–1 h−1. Mechanistic study reveals that Ag clusters accelerate the separation and migration of photogenerated carriers, and enhance the adsorption of CO2. Moreover, the Ag-O hybridization promotes the multiple-proton–electron coupling transfer process by effectively stabilizing intermediates and facilitating *CO hydrogenation to *CHO, resulting in selective CO2 reduction to CH4. This work provides a new insight into the development of selective photocatalytic conversion of CO2 to methane by constructing supported cluster catalysts.

Strategies to Improve the Activity of Silver–loaded Calcium Titanate Crystal Photocatalyst for Photocatalytic Reduction of Carbon Dioxide with Water

AbstractThe rapid increase of carbon dioxide (CO2) in the atmosphere has sparked a global enthusiasm for carbon recycling. Photocatalytic CO2 reduction with water into carbon–containing products has attracted much attention since it can convert solar energy to the chemical potential of the products and CO2 to valuable compounds at the same time. One of the main products in the photocatalytic reaction system is carbon monoxide (CO), a useful compound for the one‐carbon chemistry and related ones. The current shortage of this system is the low production efficiency, demanding us to improve the activity of the photocatalyst. In this perspective article, by taking a calcium titanate (CaTiO3, CTO) photocatalyst with silver cocatalyst (Ag/CTO) and so on as examples that can promote the selective photocatalytic CO2 reduction with water, we shortly review some strategies to improve the photocatalytic activity such as fabrication of well–structured crystal photocatalysts, development of the surface property and cocatalyst, improvement of surface CO2 adsorption, and improvement of photoabsorption. These concepts will be widely applied and contribute to further development of photocatalytic systems.

The cooperative performance of iodo and copper in a Zr-based UiO-67 metal-organic framework for highly selective photocatalytic CO2 reduction to methanol

Photocatalytic CO2 reduction (PCR) to fuels using metal-organic frameworks (MOFs) offers promising solutions for both enhancing energy supply and mitigating global warming. However, research addressing the selectivity towards MeOH production, the role of CO2 uptake in productivity, and the identification of intermediates remains limited. Herein, we present an iodo/copper functionalization strategy for the Zr-based UiO-67 MOF. The resulting bifunctional Cu/I2-Zr-BPDC/BPyDC exhibited remarkable selectivity in light-driven CO2 reduction to MeOH, revealing the first investigation of halogen bonding's effect on PCR. Crucially, Cu/I2-Zr-BPDC/BPyDC surpassed not only pristine Zr-BPyDC, I2-Zr-BPDC, and Cu-Zr-BPyDC, but also boasted the best catalytic performance among reported MOFs. Furthermore, Cu/I2-Zr-BPDC/BPyDC demonstrated a CO2 uptake capacity of 48.6 mg g−1, 1.7 times greater than non-modified Zr-BPyDC, suggesting a direct correlation between CO2 adsorption efficiency and CO2 conversion. In addition to assigning CuII ↔ CuI catalytic cycle, collaborative performance of I and Cu functions in CO2 activation was traced by infrared spectra that elucidate the CI…OCO interaction and Cu…CO2/CuCO2H complex formation. This work provides valuable insights for engineering selective and high-performance PCR catalyst through the rational incorporation of functionalities within MOFs.

Fabrication of Ce-doped UiO-66-NH2 for highly efficient and selective photocatalytic reduction of CO2 to CH4

Defect engineering by creating oxygen vacancies (OVs) and heterogeneous frustrated Lewis acid-base pairs (FLPs) emerged as an efficient strategy to enhance the selective conversion CO2 to CH4. Considering the intrinsic FLPs contained in UiO-66-NH2 (UNH for abbreviation), in this paper, the OVs was introduced therein by fabricating the Ce-doped UNH (denoted as UNH(Ce/Zr)) via one-step solvothermal route. The as-prepared UNH(Ce/Zr) catalyst exhibited the CH4 yield of 31.02 μmol·g−1·h−1 accompanied with the CH4 selectivity of 93 % and satisfying recycling stability. The XRD, SEM, FT-IR, XPS, TG, TPD and NH3 in situ DRIFTS and in situ FT-IR characterization results justified that the UNH(Ce/Zr) possess the obviously increased OVs sites and enhanced Lewis acidic and basic properties. Additionally, the photoelectrochemical characterization results showed that UNH(Ce/Zr)−0.014 efficiently improved photogenerated electron-hole separation efficiency and charge transfer rate. It could be concluded that it was the cooperative action of OVs and FLPs that led to the high CH4 selectivity and CH4 yield.

Unraveling the Transformation from Type-II to Z-Scheme in Perovskite-Based Heterostructures for Enhanced Photocatalytic CO2 Reduction.

The ability to create perovskite-based heterostructures with desirable charge transfer characteristics represents an important endeavor to render a set of perovskite materials and devices with tunable optoelectronic properties. However, due to similar material selection and band alignment in type-II and Z-scheme heterostructures, it remains challenging to obtain perovskite-based heterostructures with a favorable electron transfer pathway for photocatalysis. Herein, we report a robust tailoring of effective charge transfer pathway in perovskite-based heterostructures via a type-II to Z-scheme transformation for highly efficient and selective photocatalytic CO2 reduction. Specifically, CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 heterostructures are synthesized and then investigated by ultrafast spectroscopy. Moreover, taking CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 as examples, operando experiments and theoretical calculations confirm that the type-II heterostructure could be readily transformed into a Z-scheme heterostructure through establishing a low-resistance Ohmic contact, which indicates that a fast electron transfer pathway is crucial in Z-scheme construction, as further demonstrated by CsPbBr3/Ag/TiO2 and CsPbBr3/MoS2 heterostructures. In contrast to pristine CsPbBr3 and CsPbBr3/TiO2, the CsPbBr3/Au/TiO2 heterostructure exhibits 5.4- and 3.0-fold enhancement of electron consumption rate in photocatalytic CO2 reduction. DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil that the superior CO selectivity is attributed to the lower energy of *CO desorption than that of hydrogenation to *HCO. This meticulous design sheds light on the modification of perovskite-based multifunctional materials and enlightens conscious optimization of semiconductor-based heterostructures with desirable charge transfer for catalysis and optoelectronic applications.

Confined bismuth single atoms and nanoparticles dual-sites constructed via reverse etching for CO2 photoreduction to CH4

Synchronizing the directional photogenerated transfer of electrons and regulating the CO2 photocatalytic reduction process are key to achieving the efficient and highly selective photocatalytic reduction of CO2. The design of highly-dispersed active sites and the efficient collaboration of multiple sites are of great importance in attaining the above target. Herein, a reverse etching route was first proposed to confine Bi single atoms and nanoparticles as dual-sites for assisting CO2 photoreduction on TiO2, avoiding the mutual masking of the active sites. The Synergism of the dual-sites achieves the hydrodeoxygenation of * COOH and ushers the directional conversion of CO2 to CH4. Highly dispersed single Bi atoms could induce the transfer of photogenerated electrons, enhance CO2 absorption, and further provide active sites for reducing CO2 to *COOH intermediates. Besides, appropriate Bi nanoparticles could promote the separation and transfer of photogenerated and inhibit the formation of hydroxyl groups; more importantly, they could promote the release of protons, which would further accelerate the conversion of *COOH to CH4. After being integrated, the optimized dual-Bi/TiO2 catalyst achieves a CH4 generation rate of 103.89 μmol·g−1·h−1 with an impressive selectivity of 96.87 % as well as remarkable durability for photocatalytic CO2 reduction. This work provides new insights into developing robust catalysts through the artful design of synergistic catalytic sites for efficient photocatalytic CO2 conversion.

The photo-decomposition and self-restructuring dynamic equilibrium mechanism of Cu2(OH)2CO3 for stable photocatalytic CO2 reduction

Developing suitable photocatalysts and understanding their intrinsic catalytic mechanism remain key challenges in the pursuit of highly active, good selective, and long-term stable photocatalytic CO2 reduction (PCO2R) systems. Herein, monoclinic Cu2(OH)2CO3 is firstly proven to be a new class of photocatalyst, which has excellent catalytic stability and selectivity for PCO2R in the absence of any sacrificial agent and cocatalysts. Based on a Cu2(OH)213CO3 photocatalyst and 13CO2 two-sided 13C isotopic tracer strategy, and combined with in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations, two main CO2 transformation routes, and the photo-decomposition and self-restructuring dynamic equilibrium mechanism of Cu2(OH)2CO3 are definitely revealed. The PCO2R activity of Cu2(OH)2CO3 is comparable to some of state-of-the-art novel photocatalysts. Significantly, the PCO2R properties can be further greatly enhanced by simply combining Cu2(OH)2CO3 with typical TiO2 to construct composites photocatalyst. The highest CO and CH4 production rates by 7.5 wt% Cu2(OH)2CO3-TiO2 reach 16.4 μmol g−1h−1 and 116.0 μmol g−1h−1, respectively, which are even higher than that of some of PCO2R systems containing sacrificial agents or precious metals modified photocatalysts. This work provides a better understanding for the PCO2R mechanism at the atomic levels, and also indicates that basic carbonate photocatalysts have broad application potential in the future.

Proton Turnover Dominated Cascade Route for CO2 Photoreduction

AbstractPhotoreduction carbon dioxide (CO2) and water (H2O) into valuable chemicals is a huge potential to mitigate immoderate CO2 emissions and energy crisis. To date, tremendous attention is concentrated on the improvement of independent CO2 reduction or H2O oxidation behaviors. However, the simultaneous control of efficient electron and hole utilization is still a huge challenge due to the complex cascade redox reactions. Here, a proton turnover exists in the whole CO2 photoreduction process is discovered, which is defined as the pivot to concatenate the hole and electron behaviors. As a demonstration of the concept, the efficient activated hydrogen (*H) production centers of copper (Cu) and rapid hydrogenation centers of nickel (Ni) are coupled by an alloying strategy, and the proton turnover behaviors could be directly determined by adjustment of the molar ratios of CuxNiy. Moreover, Cu3Ni1–TiO2 exhibits the highest electron selectivity of 93.7% for methane (CH4) production with a rate of 175.9 µmol g−1 h−1, while Cu1Ni5–TiO2 reaches up to the highest carbon monoxide (CO) electron selectivity and generation rate at 84.4% and 164.6 µmol g−1 h−1, respectively. Consequently, the experimental and theoretical analysis all clarify the predominate proton turnover effect during the overall CO2 photoreduction process, which directly determines the categories and generated efficiency of C‐based products by regulating variable reaction pathways. Therefore, the revelation of the proton turnover pivot could broaden the new sights by bidirectional optimization of dynamics during the overall CO2 photoreduction system, which favors the efficient, selective, and stable photocatalytic CO2 reduction with H2O.