C1 Generation Research Articles

Chiral Nanostructured Ag Films for Multicarbon Products from CO2 Electroreduction.

The formation of multicarbon products from CO2 electroreduction is challenging on materials other than Cu-based catalysts. Ag has been known to be a typical metal catalyst, producing CO in CO2 electroreduction. The formation of C2+ products by Ag has never been reported because the carbon-carbon (C-C) coupling is an unfavorable process due to the high reaction barrier energy of *OCCO. Here, we propose that the chirality-induced spin polarization of chiral nanostructured Ag films (CNAFs) can promote the formation of triplet OCCO by regulating its parallel electron spin alignment, and the helical lattice distortion of nanostructures can decrease the reaction energy of *OCCO, which triggers C-C coupling and promotes subsequent *OCCO hydrogenation to facilitate the generation of C2+ products. The CNAFs with helically lattice-distorted nanoflakes were fabricated via electrodeposition using phenylalanine as the symmetry-breaking agent. C2+ products (C2H4, C2H6, C3H8, C2H5OH, and CH3COOH) with a Faradaic efficiency of ∼4.7% and a current density of ∼22 mA/cm2 were generated in KHCO3 electrolytes under 12.5 atm of CO2 (g). Our findings propose that the chiral nanostructured materials can regulate the multifunctionality of catalytic performance in the catalytic reactions with triplet intermediates and products.

Exchange of CO2 with CO as Reactant Switches Selectivity in Photoreduction on Co–ZrO2 from C1–3 Paraffin to Small Olefins

Photocatalytic reduction of CO2 into C2,3 hydrocarbons completes a C‐neutral cycle. The reaction pathways of photocatalytic generation of C2,3 paraffin and C2H4 from CO2 are mostly unclear. Herein, a Co0–ZrO2 photocatalyst converted CO2 into C1–3 paraffin, while selectively converting CO into C2H4 and C3H6 (6.0 ± 0.6 μmol h−1 gcat−1, 70 mol%) only under UV–visible light. The photocatalytic cycle was conducted under 13CO and H2, with subsequent evacuation and flushing with CO. This iterative process led to an increase in the population of C2H4 and C3H6 increased up to 61–87 mol%, attributed to the accumulation of CH2 species at the interface between Co0 nanoparticles and the ZrO2 surface. CO2 adsorbed onto the O vacancies of the ZrO2 surface, with resulting COH species undergoing hydrogenation on the Co0 surface to yield C1–3 paraffin using either H2 or H2O (g, l) as the reductant. In contrast, CO adsorbed on the Co0 surface, converted to HCOH species, and then split into CH and OH species at the Co and O vacancy sites on ZrO2, respectively. This comprehensive study elucidates intricate photocatalytic pathways governing the transformation of CO2 into paraffin and CO to olefins.

Exchange of CO2with CO as Reactant Switches Selectivity in Photoreduction on Co-ZrO2from C1-3Paraffin to Small Olefins.

Photocatalytic reduction of CO2 into C2,3 hydrocarbons completes a C-neutral cycle. The reaction pathways of photocatalytic generation of C2,3 paraffin and C2H4 from CO2 are mostly unclear. Herein, a Co0-ZrO2 photocatalyst converted CO2 into C1-3 paraffin, while selectively converting CO into C2H4 and C3H6 (6.0 ± 0.6 μmol h-1 gcat-1, 70 mol%) only under UV-visible light. The photocatalytic cycle was conducted under 13CO and H2, with subsequent evacuation and flushing with CO. This iterative process led to an increase in the population of C2H4 and C3H6 increased up to 61-87 mol%, attributed to the accumulation of CH2 species at the interface between Co0 nanoparticles and the ZrO2 surface. CO2 adsorbed onto the O vacancies of the ZrO2 surface, with resulting COH species undergoing hydrogenation on the Co0 surface to yield C1-3 paraffin using either H2 or H2O (g, l) as the reductant. In contrast, CO adsorbed on the Co0 surface, converted to HCOH species, and then split into CH and OH species at the Co and O vacancy sites on ZrO2, respectively. This comprehensive study elucidates intricate photocatalytic pathways governing the transformation of CO2 into paraffin and CO to olefins.

Theoretical investigation of sustainable CO2 electroreduction to high-value products utilizing N-doped/BN-modified Triphenylene-Graphdiyne catalysts

The potential of carbon-based triphenylene-graphdiyne (tpGDY) and its derivatives for the electrochemical CO2 reduction reaction (eCO2R) was comprehensively explored using density functional theory (DFT) calculations. Six variants were studied: pristine tpGDY, tpGDY-BN, tpGDY-N01, tpGDY-N02, tpGDY-N08, and tpGDY-BN-B01. Pristine tpGDY, tpGDY-BN, and tpGDY-N08 exhibited exceptional catalytic activity, efficiently converting CO2 into CO and HCOOH without external energy input. Significantly, N-doped tpGDY catalysts incorporating sp2-hybridized nitrogen atoms at the acetylenic sites (tpGDY-N01 and tpGDY-BN-N01) demonstrated remarkable electrocatalytic activity for the targeted conversion of CO2 to CH3OH. This outstanding performance is further corroborated by the low limiting potentials of −0.18 V and −0.27 V for tpGDY-N01 and tpGDY-BN-N01, respectively, highlighting their economic viability. Furthermore, the feasibility of C2 production (e.g., C2H5OH, C2H4 and C2H6) through C–C coupling of *CHO+*CO intermediate was investigated for tpGDY-N01 and tpGDY-BN-N01. DFT calculations suggest these pathways are achievable but require potentials of 0.84 V and 0.71 V for tpGDY-N01 and tpGDY-BN-N01, respectively. This study demonstrates the efficacy of N-doped tpGDY as a metal-free electrocatalyst for CO2 reduction, enabling the generation of both C1 and C2 products. This discovery holds significant promise for the advancement of sustainable CO2 conversion technologies.

Thermally induced release and generation of CO2 and C1–C4 hydrocarbons in Opalinus Clay from Mont Terri (Switzerland)

Claystone formations are candidate host rocks for high-level heat-emitting nuclear waste (HLW). Temperatures from 90 to 150 °C at the canister surface are discussed internationally as potential emplacement and storage conditions. The thermal energy emitted from waste containers will be transported into the host rock formation, accelerating chemical reactions including the release of sorbed and dissolved gases and the generation of new gases. This study investigated gas release and generation in Opalinus Clay from Mont Terri (Switzerland) at elevated temperature and pressure conditions relevant for HLW storage and beyond. Hydrous pyrolysis experiments were conducted in Dickson-type flexible gold-titanium reaction cells and gold capsules in the temperature range of 80–345 °C and at 20 MPa. CO2(g) was the predominant product, followed by C1–C4 hydrocarbons, which decrease in abundance with increasing carbon atom number. Neither CO nor H2S was detected. H2 was generated only in high temperature experiments at 315 °C and 345 °C, respectively. A combination of CO2(g) quantification, stable carbon isotopic composition data, thermodynamic calculations and aqueous fluid composition (dissolved ions, pH) demonstrated that ≥80 % of the measured CO2(g) originated from carbonate mineral dissolution. The model calculations also suggest that the fraction of CO2(aq) in DIC increases from ∼50 % at 80 °C to nearly 100 % at higher temperatures. Thermal transformation of organic matter represented an additional source for CO2(g) and was the predominant process yielding the C1–C4 hydrocarbons. Our findings stress the importance of quantitative geochemical data for the safety assessment of potential host rocks for HLW storage. We demonstrated that two sources are involved in gas release and generation at temperatures relevant for HLW storage, e.g., in the Opalinus Clay – organic matter and carbonate minerals. Our data will contribute to numerical modelling studies and the refinement of feature, events, and processes (FEP) catalogues.

Study on the Synergistic Effect of SiO2 and H2O on Oxidative Coupling of Methane over Mn-Na2WO4/SiO2 Catalyst.

Mn-Na2WO4-based catalysts with different supports were prepared using the incipient wetness impregnation method and evaluated for their oxidative coupling of methane (OCM) reaction performance. The results demonstrated that the SiO2- supported catalyst exhibited the best catalytic performance, and the introduction of H2O further enhanced its activity. Under the conditions of a feed gas mixture of CH4/O2/H2O = 6:1:24 at 800 °C and atmospheric pressure, the CH4 conversion and C2+ selectivity over the Mn-Na2WO4/SiO2 catalyst increased from 28.4% and 77.4% (without H2O) to 33.2% and 84.9%, respectively. In contrast, the catalytic activity using TiO2 and MgO supports drastically declined. Characterizations using X-ray diffraction (XRD), in situ infrared spectroscopy (In-situ IR), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), and oxygen temperature-programmed desorption (O2-TPD) revealed that the introduction of steam not only served as a diluent to decrease the partial pressures of the reactants CH4 and O2, thereby reducing deep oxidation reactions in the gas phase, but also interacted with surface oxygen species (O2 2-) and silica to form adjacent surface-bonded disilanol free radicals Si-OIH. This interaction facilitated the dehydrogenation and coupling of two methane molecules on the catalyst surface, resulting in the generation of C2+ products, significantly enhancing the catalytic activity and selectivity of OCM.

Quantitative Analysis and Manipulation of Alkali Metal Cations at the Cathode Surface in Membrane Electrode Assembly Electrolyzers for CO2 Reduction Reactions.

The stable operation of the CO2 reduction reaction (CO2RR) in membrane electrode assembly (MEA) electrolyzers is known to be hindered by the accumulation of bicarbonate salt, which are derived from alkali metal cations in anolytes, on the cathode side. In this study, we conducted a quantitative evaluation of the correlation between the CO2RR activity and the transported alkali metal cations in MEA electrolyzers. As a result, although the presence of transported alkali metal cations on the cathode surface significantly contributes to the generation of C2+ compounds, the rate of K+ ion transport did not match the selectivity of C2+, suggesting that a continuous supply of high amount of K+ to the cathode surface is not required for C2+ formation. Based on these findings, we achieved a faradaic efficiency (FE) and a partial current density for C2+ of 77 % and 230 mA cm-2, respectively, even after switching the anode solution from 0.1 M KHCO3 to a dilute K+ solution (<7 mM). These values were almost identical to those when 0.1 M KHCO3 was continuously supplied. Based on this insight, we successfully improved the durability of the system against salt precipitation by intermittently supplying concentrated KHCO3, compared with the continuous supply.

Highly Selective Production of C2+ Oxygenates from CO2 in Strongly Acidic Condition by Rough Ag-Cu Electrocatalyst.

The acidic electrocatalytic conversion of CO2 to multi-carbon (C2+) oxygenates is of great importance in view of enhancing carbon utilization efficiency and generating products with high energy densities, but suffering from low selectivity and activity. Herein, we synthesized Ag-Cu alloy catalyst with highly rough surface, by which the selectivity to C2+ oxygenates can be greatly improved. In a strongly acidic condition (pH=0.75), the maximum C2+ products Faradaic efficiency (FE) and C2+ oxygenates FE reach 80.4 % and 56.5 % at -1.9 V versus reversible hydrogen electrode, respectively, with a ratio of FEC2+ oxygenates to FEethylene up to 2.36. At this condition, the C2+ oxygenates partial current density is as high as 480 mA cm-2. The in situ spectra, control experiments and theoretical calculations indicate that the high generation of C2+ oxygenates over the catalyst originates from its large surface roughness and Ag alloying.

Compressive strain in Cu catalysts: Enhancing generation of C2+ products in electrochemical CO2 reduction

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO2 reduction reaction (eCO2RR), particularly toward the formation of multicarbon (C2+) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to CuxO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm2 and Faradaic efficiency exceeding 80% were realized for the C2+ products. The selectivity ratio of C2+/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K+ ion-hydrated water (K·H2O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C–C coupling and enhancing the yield of C2+ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO2RR.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals.

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

Promoting CO Electroreduction to C2+ Oxygenates by Distribution of Water Dissociation Sites.

The electrocatalytic CO2 or CO reduction reaction is a complex proton-coupled electron transfer reaction, in which protons in the electrolyte have a critical effect on the surface adsorbed *H species and the multi-carbon oxygenate products such as ethanol. However, the coupling of *H and carbon-containing intermediates into C2+ oxygenates can be severely hampered by the inappropriate distributions of those species in the catalytic interfaces. In this work, the controlled distribution of highly dispersed CeOx nanoclusters is demonstrated on Cu nanosheets as an efficient CO electroreduction catalyst, with Faradaic efficiencies of ethanol and total oxygenates of 35% and 58%, respectively. The CeOx nanoclusters (2-5 nm) enabled efficient water dissociation and appropriate distribution of adsorbed *H species on the Cu surface with carbon-containing species, thus facilitating the generation of C2+ oxygenate products. In contrast, pristine Cu without CeOx tended to form ethylene, while the aggregated CeOx nanoparticles promoted the surface density of *H and subsequent H2 evolution.

Tailoring the catalytic microenvironment of CuO with hydrophobic CuSA2 for selective CO2 electroreduction to C2+ products

Advancing the Faraday efficiency (FE) and current density of Cu catalyzed electrochemical CO2 reduction (ECR) reaction to produce C2+ products is important for its practical applications. Constructing a hydrophobic interface to regulate the local reaction environment is an effective method to improve the selectivity of C2+ products, but it is limited by the low reaction current density. In this work, we fabricated a novel hydrophobic and ECR active copper stearate (CuSA2) decorated CuO nanoparticle catalyst (CuO/CuSA2) for ECR reaction toward C2+ products. As a result, the CuO/CuSA2 catalyst achieved an FE of 61.33 % and a partial current density of 429.33 mA cm−2 for C2+ products. The CuSA2 and CuO nanoparticle cooperate very well for the formation of C2+ products. The in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and electrochemical adsorption experiment indicated that the hydrophobic CuSA2 regulated the local ECR reaction environment. The local ∗CO2.- and *CO adsorption were strengthened by hydrophobic CuSA2 modification while the H2O adsorption was inhibited. CuO nanoparticle promotes *CO coupling reaction and enhances C2 intermediates (*OCCOH and *OC2H5) adsorption. Hydrophobic CuSA2 and CuO nanoparticle synergistically promote the generation of C2+ products. This work provides new insights into the design of hydrophobic CO2 reduction electrocatalysts for the preparation of C2+ products.

The Role of Phase Mixing Degree in Promoting C-C Coupling in Electrochemical CO2 Reduction Reaction on Cu-based Catalysts.

Cu-based catalysts have been identified as the most promising candidates for generation of C2+ products in electrochemical CO2 reduction reaction. Defect engineering in catalysts is a widely employed strategy for promoting C-C coupling on Cu. However, comprehensive understanding of defect structure-to-activity relationship has not been obtained. In this study, controllable defects generation is achieved, which leads to a series of Cu-based catalysts with various phase mixing degrees. It is observed that the Faradaic efficiency toward C2+ products increases with the phase mixing degree, reaching 81 % at maximum. In situ infrared absorption spectroscopy reveals that the catalysts with higher phase mixing degree tend to form *CO more easily and possess higher retention of *CO under high overpotential window, thereby promoting C-C coupling. This work sheds new light on the relationship between defects and C-C coupling, and the rational developed of more advanced Cu-base catalysts.

The Role of Phase Mixing Degree in Promoting C−C Coupling in Electrochemical CO2 Reduction Reaction on Cu‐based Catalysts

AbstractCu‐based catalysts have been identified as the most promising candidates for generation of C2+ products in electrochemical CO2 reduction reaction. Defect engineering in catalysts is a widely employed strategy for promoting C−C coupling on Cu. However, comprehensive understanding of defect structure‐to‐activity relationship has not been obtained. In this study, controllable defects generation is achieved, which leads to a series of Cu‐based catalysts with various phase mixing degrees. It is observed that the Faradaic efficiency toward C2+ products increases with the phase mixing degree, reaching 81 % at maximum. In situ infrared absorption spectroscopy reveals that the catalysts with higher phase mixing degree tend to form *CO more easily and possess higher retention of *CO under high overpotential window, thereby promoting C−C coupling. This work sheds new light on the relationship between defects and C−C coupling, and the rational developed of more advanced Cu‐base catalysts.

Coordination Environment Engineering of Metal Centers in Coordination Polymers for Selective Carbon Dioxide Electroreduction toward Multicarbon Products.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) toward value-added chemicals/fuels has offered a sustainable strategy to achieve a carbon-neutral energy cycle. However, it remains a great challenge to controllably and precisely regulate the coordination environment of active sites in catalysts for efficient generation of targeted products, especially the multicarbon (C2+) products. Herein we report the coordination environment engineering of metal centers in coordination polymers for efficient electroreduction of CO2 to C2+ products under neutral conditions. Significantly, the Cu coordination polymer with Cu-N2S2 coordination configuration (Cu-N-S) demonstrates superior Faradaic efficiencies of 61.2% and 82.2% for ethylene and C2+ products, respectively, compared to the selective formic acid generation on an analogous polymer with the Cu-I2S2 coordination mode (Cu-I-S). In situ studies reveal the balanced formation of atop and bridge *CO intermediates on Cu-N-S, promoting C-C coupling for C2+ production. Theoretical calculations suggest that coordination environment engineering can induce electronic modulations in Cu active sites, where the d-band center of Cu is upshifted in Cu-N-S with stronger selectivity to the C2+ products. Consequently, Cu-N-S displays a stronger reaction trend toward the generation of C2+ products, while Cu-I-S favors the formation of formic acid due to the suppression of C-C couplings for C2+ pathways with large energy barriers.

(Keynote) Metal Enhanced Cr2O3/Ga2O3 an Efficient and Selective Electrocatalyst for the Conversion of CO2 to C2+ Products

Binary intermetallic compounds composed of a first row transition metal and a post transition metal such as aluminum or gallium and oxides thereof provide a new source of heterogeneous electrocatalysts for the reduction of CO2. Unlike related single metal systems, which only generate formate and CO, the mixed metal systems form a variety of C2+ products. Most interestingly, we find that a nickel metal enhanced Cr2O3/Ga2O3 interface efficiently catalyzes the formation of 1-butanol.We have reported that Ni3Al reduces CO2 to a variety of C3 oxygenates,1-2 while Lewis et. al. has noted that various NixGay alloys generate C2 products from CO2.3 In both cases, the higher order products are observed in low yield. However, these examples are important since they demonstrate that metallic systems that do not contain copper can form carbon-carbon bonds from CO2. Recently, we discovered that mixed oxides of chromium-gallium containing a small concentration of nickel metal produce 1-butanol with greater than 40% faradaic yields in aqueous electrolytes.4 A variety of other C2, C3 and C4 products are also observed. These species can be selected for, by regulating the electrolyte pH, the electrode potential and the enhancing metal employed.Our new findings argue for a relatively unexplored mechanism for the formation of carbon-carbon bonds through a formate intermediate, circumventing the need to generate a CO. For all of the heterogeneous systems we have investigated, there appears to be strong correlation between the morphology of the electrocatalyst and the product distribution observed. It is also observed that the composition of the underlying electrode strongly influences the product composition. For example, while Ni3Al on glassy carbon produces a variety of C3 products, the same catalyst when placed on p-type CIGS photocathode primarily produces methanol with no indication of carbon-carbon coupling processes.5 A detailed mechanistic understanding of these systems is likely to offer new opportunities for the electrosynthesis of organic products from CO2 with high faradaic yield and modest overpotential.References Paris, A. R.; Bocarsly, A. B., Ni–Al Films on Glassy Carbon Electrodes Generate an Array of Oxygenated Organics from CO2. ACS Catalysis 2017, 7, 6815-6820. Paris, A. R.; Bocarsly, A. B., Mechanistic Insight into C2 and C3 Product Generation Using Ni3Al and Ni3Ga Electrocatalysts for CO2 Reduction. In Faraday Discussion on Artifical Photosynthesis, Royal Society of Chemistry: Cambridge University, GB, 2018. Torelli, D. A.; Francis, S. A.; Crompton, J. C.; Javier, A.; Thompson, J. R.; Brunschwig, B. S.; Soriaga, M. P.; Lewis, N. S., Nickel–Gallium-Catalyzed Electrochemical Reduction of CO2 to Highly Reduced Products at Low Overpotentials. ACS Catalysis 2016, 6 (3), 2100-2104. Cronin, S. P.; Dulovic, S.; Lawrence, J. A.; Filsinger, K. A.; Hernandez-Gonzalez, A. P.; Evans, R.; Stiles, J. W.; Morris, J.; Pelczer, I.; Bocarsly, A. B., Direct Synthesis of 1-butanol with High Faradaic Efficiency from CO2 Utilizing Cascade Catalysis at a Ni-Enhanced (Cr2O3)3Ga2O3 Electrocatalyst. J. Am. Chem. Soc. 2023, 6762–6772. Foster, B. M.; Paris, A. R.; Frick, J. J.; Blasini-Pérez, D. A.; Cava, R. J.; Bocarsly, A. B., Catalytic Mismatching of CuInSe2 and Ni3Al Demonstrates Selective Photoelectrochemical CO2 Reduction to Methanol. ACS Applied Energy Materials 2020, 3 (1), 109-113.

(Invited) Exploring Solar-Driven CO2 Reduction to C2+ Products

Use of solar irradiance to drive CO2 reduction (CO2R) holds great promise for the sustainable generation of energy-dense fuels and chemicals, especially as it relates well to carbon capture technology. Multicarbon (C2+) products (e.g., ethylene, ethanol, propanol) are particularly attractive because they have a large market size and can be further converted to higher molecular weight hydrocarbons fuels that have high volumetric and mass energy densities. Metallic copper (Cu) has the unique ability to catalyze CO2 to C2+ products with high faradaic efficiency; however, the product distribution of CO2R on Cu is potential and microenvironment dependent. In this talk, we will explore CO2R via different routes using both experiments and simulation. We will focus on obtaining C2+ products via tailoring the microenvironments including the use of ionomer films that are quite effective at the lower current densities that match against the solar irradiance. We will demonstrate how control of the local environment and dynamic operation provide metastable states of high pH and high CO2 concentration, thereby enabling high CO2R to C2+ production.In addition, for direct photoelectrochemical CO2R, there is an optimum cell design and operating photovoltage that is not at the maximum power point (unlike water splitting) due to the selectivity dependence on potential. Using a continuum model of PEC CO2R, we will explore the co-design of the photoelectrode bandgaps and device architecture for the generation of C2+ products. The simulation results demonstrate the critical importance of simultaneously engineering the photoelectrode and device design and operation in order to ensure the photovoltage and photocurrent from the photoelectrode enables operation at the optimum potential. Finally, for PEC CO2R, we will explore the use of metal-insulator-semiconductor (MIS) structures to obtain high rates of CO2R. This includes both theoretical and experimental investigations that elucidate the controlling phenomena and when coupled with the ionomer films provide high rates of direct PEC CO2R. Overall, the insights between the photoelectrode and device design is critical for the design of monolithic, unassisted PEC CO2R systems that yield high STC2+ efficiency.AcknowledgementsThis material is based partially on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266 and a University of California grant.

Comprehensive Insight into Construction of Active Sites toward Steering Photocatalytic CO2 Conversion

AbstractPhotoreduction of CO2 into hydrocarbon fuels is a promising avenue for achieving a sustainable alternative to the artificial carbon cycle. Photocatalytic CO2 conversion is the chemical transformation of photogenerated carriers and adsorbed CO2 at active sites of catalysts. Active sites can regulate the kinetic process of carriers, control the adsorption of CO2 and intermediates, lower activation barriers, and promote C‐C coupling. This review mainly concentrates on the efficiency and selectivity regulation of the target products through construction of active sites. First, the principles of CO2 photoreduction, such as the influencing factors and specific pathways for monocarbon and multicarbon (C2+) formation, are discussed. Then, leading works focusing on improving catalytic efficiency and regulating product selectivity through the introduction of active sites are highlighted, concerning the underlying mechanism of the performance, especially for C2+ generation. Subsequently, an overview of the currently available in situ techniques and theoretical calculation for identifying the active sites are provided. Finally, the challenges of emerging strategies to achieve carbon recycling from scientific, technical, and economic perspectives are considered. This review offers deep insight into the construction of active site with atomic precision to achieve efficient photocatalytic CO2 conversion and the generation of C2+ in high selectivity.

Tailoring the *CO and *H Coverage for Selective CO2 Electroreduction to CH4 or C2H4.

In the electrochemical CO2 reduction reaction (CO2RR), the coverages of *CO and *H intermediates on a catalyst surface are critical for the selective generation of C1 or C2 products. In this work, we havesynthesized several CuxZnyMnz ternary alloy electrocatalysts, including Cu8ZnMn, Cu8Zn6Mn, and Cu8ZnMn2, by varying the doping compositions of Zn and Mn, which are efficient in binding *CO and *H adsorbates in the CO2 electroreduction process, respectively. The increase of *H coverage allows to promotion of the CH4 and H2 formation, while the increase of the *CO coverage facilitates the production of C2H4 and CO. As a result, the Cu8ZnMn catalyst presented a high CO2-to-CH4 partial current density (-418±22mAcm-2) with a Faradaic efficiency of 55±2.8%, while the Cu8Zn6Mn catalyst exhibited a CO2-to-C2H4 partial current density (-440±41mAcm-2) with a Faradaic efficiency of 58±4.5%. The study suggests a useful strategy for rational design and fabrication of Cu electrocatalysts with different doping for tailoring the reduction products.

CO2 reduction employing MgH2 for CH4–H2 mixtures production through mechano-chemical processes

The CO2 methanation employing MgH2 as a source of hydrogen is investigated via mechano-chemical processes through ball milling at room temperature under different experimental conditions such as the presence/absence of catalyst, the milling duration, the molar ratio between the hydride and CO2 and the pre-milling of Ni–MgH2 mixture. The positive effect of Ni addition is demonstrated. After 5h of milling under CO2, the absence of catalyst causes the CH4 yield to drop from 70.0 to 59.0%, from 73.0 to 33.5% and from 54.0 to 40.1%, considering molar ratios of 4:1, 3:1 and 2:1, respectively. The pre-milling of nickel-catalyzed system or the addition of CNTs do not provide significant improvements. This investigation shows that similar methane yields to those obtained by thermo-chemical methods can be achieved, but involving shorter times (5 h versus 24 h) and lower temperatures (room temperature versus 400 °C). The ball collisions during milling allow overcoming passivation phenomena of MgH2 and Mg, promoting the methanation process but with lower selectivity as contamination with Fe from the milling jar provides a catalytic alternative route for the generation of C2–C3 hydrocarbons.