CO2 Reduction Pathway Research Articles

Dissimilatory manganese reduction facilitates synergistic cooperation of hydrolysis, acidogenesis, acetogenesis and methanogenesis via promoting microbial interaction during anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) of waste activated sludge (WAS) is commonly limited to poor synergistic cooperation of four stages including hydrolysis, acidogenesis, acetogenesis and methanogenesis. Dissimilatory metal reduction that induced by metal-based conductive materials is promising strategy to regulate anaerobic metabolism with the higher metabolic driving force. In this study, MnO2 as inducer of dissimilatory manganese reduction (DMnR) was added into WAS-feeding AD system for mediating complicated anaerobic metabolism. The results demonstrated that main operational performances including volatile solid (VS) degradation efficiency and cumulative CH4 production with MnO2 dosage of 60 mg/g·VS reached up to maximum 53.6 ± 3.4% and 248.2 ± 10.1 mL/g·VS while the lowest operational performances in control group (38.5 ± 2.8% and 183.5 ± 8.5 mL/g·VS) was originated from abnormal operation of four stages. Furthermore, high-throughput 16 S rRNA pyrosequencing revealed that enrichment of dissimilatory manganese-reducing contributors and methanogens such as Thermovirga, Christensenellaceae_R_7_group and Methanosaeta performed the crucial role in short-chain fatty acids (SCFAs) oxidation and final methanogenesis, which greatly optimized operational environment of hydrolysis, acidogenesis and acetogenesis. More importantly, analysis of functional genes expression proved that abundances of genes encoding enzymes participated in acetate oxidation, direct interspecies electron transfer (DIET) and CO2 reduction pathway were simultaneously up-regulated with the optimum MnO2 dosage, suggesting that DMnR with SCFAs oxidation as electron sink could benefit stable operation of four stages via triggering effective DIET-based microbial interaction mode.

DFT approach to the stability, the structural, electronic and photocatalytic properties of the ZnV2O6(001) surface terminations

The ZnV2O6 of (001) different surface terminations and the CO2 reduction process were examined using the first principles. We explored the several (001) surface terminations of ZnV2O6 and discovered that the surface terminated in O is the most stable. Although the light absorption coefficient of the surface terminated in Zn is significantly higher in the visible region than that of the surface terminated in O, and the work function is lower, the surface terminated in O has a preferable band gap (2.113 eV) for the photocatalytic reaction and the most stable surface energy. The adsorption and reduction mechanisms of CO2 on a ZnV2O6(001) terminated in O surface were examined, and the species tends to bind to O sites on the surface and form C–O or O–H bonds. CO2→COOH*→HCOOH*→HCO*→H2CO→CH2OH*→CH3OH is the best reaction pathway for CO2 reduction on surfaces terminated in O, and the hydrogenation of COOH* to HCOOH is the rate-determining step with a maximum ΔG and a 4.16 eV energy barrier. ZnV2O6(001) could be a decent candidate for a CO2 to methanol catalyst. As a conclusion, ZnV2O6(001) can be employed as a potential catalyst for converting carbon dioxide to methanol, and theoretical part of the ZnV2O6(001) interaction system has been expanded.

Multichannel electron transmission and multiple light scattering in CoCo PBA/CoSn(OH)6/Pt photocatalyst for effective conversion of simulated flue gas

Converting industrial waste gas into high-value chemicals is crucial to sustainable economic development. Herein, through a coordination strategy of facet-selective etching and in-situ growth, the CoCo Prussian blue analogue (PBA)/CoSn(OH)6/Pt heterojunction was designed and prepared with multiple interfaces and dual interconnection networks, which is suitable for photocatalytic conversion of simulated flue gas. This unique structure is conducive to multi-channel electron transmission and multiple light scattering, promoting the separation and migration of photogenerated carriers. This photocatalyst can synergistically regulate charge potential and kinetics, and enhance CO2 activation. Therefore, the CO generation rate (11.7 µmol·g−1·h−1) and selectivity (91.8 %) of the CoCo PBA/CoSn(OH)6/Pt heterojunction were significantly improved without using additional photosensitizer or sacrificial agent. The mechanism and reaction pathway of photocatalytic CO2 reduction were further studied by in-situ technology and density functional theory (DFT) calculation. This study offers knowledge about the preparation of high-efficiency photocatalysts for flue gas conversion and structure-modulated photocatalytic reaction.

Host‐guest tuning of the CO2 reduction activity of an iron porphyrin cage

AbstractEfficient electrocatalytic CO2 reduction requires developing catalysts with high selectivities and high activities, which is simultaneously difficult to achieve. Here, we present a new approach to tune the CO2 reduction activity based on host‐guest chemistry enabled by an iron porphyrin cage catalyst. The cage design allows the hosting of alkali metals in the side walls causing a change in the electrostatic potential inside the cage cavity. Density functional theory calculations show that the guest potassium ions assist the reduction of CO2 by inverting the two‐electron transfer from iron(0) to CO2 from endothermic to exothermic. Accordingly, electrochemical experiments with the cage catalyst show that in the presence of the potassium ions, the overpotential for the CO2 reduction decreases, and the catalytic activity increases while the high selectivity of the cage is retained. A novel coupling between the electrochemical cell and a mass spectrometer allowed the trapping of the key intermediates. Cryogenic ion spectroscopy characterization of the intermediates showed the details of the potassium ions hosting in the reduced cage and of the stabilization of the Fe‐COOH intermediates by the interaction with the potassium ions at the single‐molecule level.Key points Host‐guest chemistry of iron porphyrin‐cage catalysts in electrocatalytic CO2 reduction results in an increase in the activity and the selectivity of the catalysis. Electrochemistry—mass spectrometry coupling allowed studying of the reaction intermediates in CO2 reduction by mass spectrometry and by helium tagging infrared photodissociation spectroscopy. DFT calculations showed the details of the CO2 reduction pathway inside of the cage cavity and the working principles of the reactivity enhancement by the host‐guest chemistry.

Proton-Coupled, Low-Energy Pathway for Electrocatalytic CO2 Reduction at Re(Diimine) Complexes with a Conjugated Pyrazinyl Moiety.

Large conjugated carbon framework has been incorporated as the diimine ligand for Re(α-diimine)(CO)3Cl complexes with a pyrazinyl linkage, either to increase energy efficiency or to turn them into heterogeneous catalysts for selective electrocatalytic CO2 reduction. However, there exists a nonmonotonic dependence of CO2 reduction overpotential on the conjugation size of the ligands. Understanding its origin could facilitate heterogenization of molecular catalysts with improved energy efficiency. Here, we show that the conjugated pyrazinyl moiety plays a crucial role in catalysis by enabling a proton-coupled, lower-energy pathway for CO2 reduction. With ligands of moderate size, the pathway leads to previously unknown intermediates and decreases CO2 reduction overpotential. Because the pathway hinges on the basicity of the pyrazinyl nitrogen, we propose that it imposes a limit on the conjugation size of the ligand for the pathway to be effective.

Cu doping and Ti3C2OH quantum dots co-modifications of Zn3In2S6 boosted photocatalytic reduction of CO2 to CO via accelerating carriers transfer and enhancing CO2 adsorption and activation

In this study, the Zn3In2S6 was modified by Cu doping and loading of Ti3C2OH quantum dots (QDs) by hydrothermal method for efficient and highly selective photoreduction of CO2. Various characterizations and tests demonstrated that the Cu0.05Zn2.95In2S6@Ti3C2OH QDs exhibited desired morphology, superior light utilization ability, and the most efficient carriers’ separation and transfer. This optimized material exhibited a CO yield of 51.848 μmol g-1 h-1, with selectivity up to 99%. This high CO yield was 22.3 and 3.48 times of those of the Zn3In2S6 and Cu0.05Zn2.95In2S6, respectively; demonstrating that synergistic effect of Cu-doping and Ti3C2OH QDs modification existed for enhancing CO2 reduction to CO. Results of CO2-TPD and in-situ FTIR showed that the Cu0.05Zn2.95In2S6@Ti3C2OH QDs possessed the greatest CO2 adsorption and activation ability. DFT (density functional theory) calculation revealed that greatest CO2 adsorption energy, CO desorption energy and charge density distribution were key factors for the Cu0.05Zn2.95In2S6@Ti3C2OH QDs to achieve efficient reduction of CO2. Possible CO2 reduction pathways and mechanism were proposed. This study could advance the development of photocatalysts for highly selective CO2 reduction to CO and enrich related mechanism insights.

Boosting Electrocatalytic Reduction of CO2 to HCOOH on Ni Single Atom Anchored WTe2 Monolayer.

Achieving efficient conversion of carbon dioxide (CO2 ) to formic acid (HCOOH) at mild conditions is a promising means to reduce greenhouse gas emission and mitigate the energy crisis. Herein, spin-polarized density functional theory calculations with van der Waals corrections (DFT+D3) are performed to analyze the catalytic activity of seven metals (Ti, Fe, Ni, Cu, Zn, In, and Sn) anchored on a tungsten ditelluride monolayer (M@WTe2 ) and screen favorable CO2 reduction pathways. These results demonstrate that Ni single atoms strongly bind to the WTe2 monolayer and exist in isolated form due to the high diffusion barriers. Also, Ni-anchored WTe2 monolayer (Ni@WTe2 ) possesses a considerably low limiting-potential (-0.11V vs reversible hydrogen electrode) to convert CO2 to HCOOH due to moderate OCHO adsorption energy and a suppressed competing hydrogen evolution reaction (HER). Therefore, Ni@WTe2 monolayer is a promising electrocatalytic material for the CO2 reduction reaction (CO2 RR). This study sheds light on strategies of designing single metal atom anchored WTe2 catalysts for improved CO2 RR performances.

Flower-like microspheres Z-scheme Bi2Sn2O7/NiAl-LDH heterojunction for boosting photocatalytic CO2 reduction under visible light

Fabrication of efficient photocatalysts with great visible light utilization ability, rapid carriers’ separation, and suitable redox potential is essential for improving photocatalytic CO2 reduction. Herein, flower-like microspheres Bi2Sn2O7/NiAl-layered double hydroxide (BSO/LDH) heterojunctions were prepared by hydrothermal process for CO2 reduction. The Bi2Sn2O7 nanoparticles were dispersed on NiAl-LDH nanosheets, with tight contact interface, which facilitated charges transfer and exposing more catalytic active sites. Results of photochemical deposition of metal/metal oxide demonstrated that interfacial charges transfer of the BSO/LDH followed Z-scheme mechanism, endowing more desired redox potential and more efficient carriers separation. The 30%-BSO/LDH showed the highest CO and CH4 yields of 37.91 and 1.18 μmol g−1 h−1 under visible light irradiation, 3.4 and 2.0 times higher than those from the NiAl-LDH, respectively. The main intermediates during CO2 reduction were carboxylate (COOH*) and aldehyde group (CHO*), and CO2 reduction pathways and mechanism were proposed accordingly. This study provided referential strategy for designing efficient heterojunction photocatalysts for CO2 conversion.

Scenario of carbon dioxide (CO2) emission peaking and reduction path implication in five northwestern provinces of China by the low emissions analysis platform (LEAP) model

Achieving global peaking of carbon dioxide (CO2) emissions as early as possible is a common goal for all countries. However, CO2 emissions in the northwest China still show a rapid growth trend. Thus, we used the Low Emissions Analysis Platform (LEAP) model to build three scenarios to investigate the peak of CO2 emissions and reduction pathways in five northwestern provinces of China. The results show that: 1) the CO2 emissions of five northwestern provinces under the baseline, the policy, and the green scenarios will peak in 2035 (1663.46 × 106 tonnes), 2031 (1405.00 × 106 tonnes), and 2027 (1273.96 × 106 tonnes), respectively. 2) The CO2 emissions of all provinces, except Qinghai, will not peak before 2030 in the baseline scenario. Under the policy and green scenarios, each province will achieve the peak of CO2 emissions by 2030. 3) The CO2 emissions from agriculture, transportation, and other sectors will peak before 2030 under the baseline scenario. The CO2 emissions from construction will peak before 2030 in policy scenario. The industry and commerce will peak before 2030 in green scenario. 4) The emission reduction effect indicates that CO2 emissions from 2020 to 2040 will be reduced by 4137.70 × 106 tonnes in the policy scenario and 7201.46 × 106 tonnes in the green scenario. The industrial coal and thermal power are the sectors with the greatest potential to reduce CO2 emissions. Accelerating the restructuring of industries and energy structures and improving technologies to reduce energy intensity can promote the achievement of the peak in CO2 emissions by 2030.

Electrocatalytic CO2 reduction to alcohols by modulating the molecular geometry and Cu coordination in bicentric copper complexes

Electrocatalytic reduction of CO2 into alcohols of high economic value offers a promising route to realize resourceful CO2 utilization. In this study, we choose three model bicentric copper complexes based on the expanded and fluorinated porphyrin structure, but different spatial and coordination geometry, to unravel their structure-property-performance correlation in catalyzing electrochemical CO2 reduction reactions. We show that the complexes with higher intramolecular tension and coordination asymmetry manifests a lower electrochemical stability and thus more active Cu centers, which can be reduced during electrolysis to form Cu clusters accompanied by partially-reduced or fragmented ligands. We demonstrate the hybrid structure of Cu cluster and partially reduced O-containing hexaphyrin ligand is highly potent in converting CO2 into alcohols, up to 32.5% ethanol and 18.3% n-propanol in Faradaic efficiencies that have been rarely reported. More importantly, we uncover an interplay between the inorganic and organic phases to synergistically produce alcohols, of which the intermediates are stabilized by a confined space to afford extra O-Cu bonding. This study underlines the exploitation of structure-dependent electrochemical property to steer the CO2 reduction pathway, as well as a potential generic tactic to target alcohol synthesis by constructing organic/inorganic Cu hybrids.

Z-scheme CoAl-layered double hydroxide/indium vanadate heterojunction for enhanced and highly selective photocatalytic reduction of carbon dioxide to carbon monoxide

Development of efficient photocatalysts is essential for carbon dioxide (CO2) photocatalytic reduction. In this study, Z-scheme CoAl-layered double hydroxide (LDH)/indium vanadate (InVO4) heterojunction photocatalysts were synthesized using hydrothermal method, and their performance toward CO2 reduction and mechanism were determined. Results of characterizations showed that the CoAl-LDH/InVO4-30 exhibited desired morphology, the most efficient photogenerated carriers separation and charge transfer, and the highest photocurrent response. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) manifested that charge transfer of the CoAl-LDH/InVO4 conformed to Z-scheme mechanism. The CoAl-LDH/InVO4-30 exhibited the highest carbon monoxide (CO) yield of 174.4 μmol g−1 within 2 h of reaction, which was 2.46 and 9.79 times of pure CoAl-LDH and InVO4, respectively. The CO selectivity was up to nearly 100%. Moreover, in-situ fourier transform infrared spectroscopy (ISFT-IR) demonstrated that bicarbonate (HCO3*) and carboxylate (COOH*) were the main intermediates during the CO2 reduction process, and possible CO2 reduction pathways were proposed. This work provides a reference for construction of Z-scheme LDH-based heterojunctions for efficient CO2 photoreduction.

Unravelling the CO2 methanation mechanisms on a Ni-BaTiO3 catalyst: A theoretical investigation

Solar-induced photothermal catalysis of CO2 reduction is an effective method for chemical CO2 conversion with great potential. Understanding its reaction mechanism is crucial for the development of new catalysts. In this work, the mechanism of CO2 reduction on a BaTiO3 supported Ni catalyst was studied using density functional theory (DFT). The presence of the BaTiO3 base was found to have great significance in the adsorption and activation of CO2. The dominant reaction pathway of CO2 reduction on the BaTiO3 supported Ni catalyst is calculated as CO2(g)→CO2→CO→COH→HCOH→CH→CH2→CH3→CH4→CH4(g) and is rate-limited by the reduction of CO, with a corresponding energy barrier of 0.94 eV, which is nearly 1.00 eV lower than that on the pure Ni surface. The BaTiO3 base not only induces wrinkling distortion of the Ni surface, which facilitates the step of CO hydrogenation, but also results in an upshift of the d-band centre and Fermi level of the catalyst, which enhances the binding strength of the catalyst with the reaction intermediates. Based on the projected density of states (PDOS) analysis, the BaTiO3 base strongly promotes the σ-bonding interaction between the Ni surface and CO. The stronger adsorption of CO on the surface of the BaTiO3 supported Ni catalyst results in the reduction reaction selectively generating CH4 but not CO.

Selective photothermal CO2 reduction to CO, CH4, alkanes, alkenes over bimetallic alloy catalysts derived from layered double hydroxide nanosheets

Photothermal catalytic reduction of CO2 with H2 as the reducing agent holds great promise for the conversion of combustion-derived CO2 into hydrocarbon fuels and other valuable commodity chemicals. Whilst a number of promising photothermal catalysts have been developed for CO2 reduction, reaction mechanisms remain elusive, and the factors controlling product selectivity are unclear. In this work, three distinct transition metal alloy nanoparticle catalysts, each supported by amorphous alumina, were fabricated by hydrogen reduction of CoFeAl-layered double hydroxide (CoFeAl-LDH), NiFeAl-LDH and NiCoAl-LDH nanosheet precursors at 650 °C. By using the different alloy nanoparticles (CoFe, NiFe or NiCo) and tuning the reaction parameters including temperature and gas flow rate during photothermal CO2 reduction with H2, different product distributions (CH4, CO, light olefins, paraffins) were obtained, with the distribution depending strongly on the alloy catalyst composition. A reaction pathway for CO2 reduction consisting of multiple steps was discovered and confirmed by in-situ diffuse reflectance infrared Fourier transform spectroscopy studies and a series of control catalytic experiments. Findings provide valuable new insights about the reaction mechanism of photothermal catalytic CO2 reduction to hydrocarbon products over metal catalysts and the factors regulating product selectivity.

A Nonaqueous Mg‐CO2 Battery with Low Overpotential

AbstractMg‐CO2 batteries, which exploit the greenhouse gas CO2 as cathode active species, are an appealing next‐generation battery candidate due to their high efficiency energy storage and value‐added CO2 utilization. However, compared with other metal‐CO2 systems, few aprotic Mg‐CO2 batteries have been reported so far as a result of several crucial problems including the comparatively slow redox reaction kinetics, a large decomposition energy barrier of the reduction products, and poor reversibility in their multi‐electron three‐phase cathodic reactions in nonaqueous environments. Herein, a rechargeable Mg‐CO2 battery is developed by using a Mo2C‐CNTs catalytic cathode, a nonaqueous electrolyte, and a magnesium metal anode. The Mo2C‐CNTs catalytic cathode can greatly reduce the charge overpotential of the Mg‐CO2 battery through tuning the CO2 reduction pathways. The results of a variety of ex situ and in situ experiments as well as theoretical calculations show the Mo2C catalyst not only induces surface molecular adsorption for faster reaction kinetics but also improves the selectivity toward MgC2O4 in the CO2 reduction process for a higher Faraday efficiency. An exceptional low voltage hysteresis is achieved for the Mg‐CO2 battery. This work demonstrates a promising strategic option for rechargeable nonaqueous Mg‐CO2 batteries for simultaneously addressing energy and environmental issues.

(Keynote) Insights into the CO2 Reduction Pathway through the Electrolysis of Aldehydes

Investigating the electrochemical reduction of aldehydes to alcohols provides insights into the mechanistic pathways of converting CO2 to alcohols electrochemically. Both acetaldehyde and propionaldehyde were electrochemically reduced on a polycrystalline Cu catalyst to illustrate that it is a viable pathway to ethanol and 1-propanol, respectively, supporting the mechanistic route previously proposed in the literature. 13C and 1H NMR analysis on isotopically labeled acetaldehyde was utilized to trace the reduction process. In an aqueous solution, acetaldehyde is at equilibrium with ethanediol, and propionaldehyde with propanediol. The dissociation of adsorbed ethanediol to acetaldehyde and water was also found to be favorable on both Cu and Au surfaces. Experimental observations were also supported with DFT calculations, indicating a higher-energy reaction intermediate on Au (111) over Cu (100). In summary, the results from this study support previously proposed mechanisms and provide a framework for testing other stable CO2 reaction intermediates to gain insights into the overall CO2 reaction pathway. Figure 1

Fabrication of hetero-metal oxide NiCo2V2O8 hollow nanospheres for efficient visible light-driven CO2 photoreduction

Design of highly efficient photocatalysts for CO2 reduction to renewable fuels has gained significant attention for energy sustainability and carbon neutralization. Here, we report the fabrication of hetero-metal oxide NiCo2V2O8 hollow nanospheres through self-templating strategy and anion-exchange reaction. The as-prepared NiCo2V2O8 hollow nanospheres exhibit remarkable CO2 photoreduction, achieving a CO generation rate of 198.65 μmol g−1 h−1 (9.64 times higher than the undoped Co3V2O8) with 98.8% selectivity under visible light irradiation. Results of experiments and density functional theory (DFT) calculations show that addition of Ni in the hetero-metal oxide and their electronic interaction among d states decrease the bandgap to extend the light absorption, promote CO2 adsorption, and favor the separation of photogenerated charges with inhibited recombination. The in situ FT-IR and Raman spectral results identify the CO2 reduction pathway through COOH* intermediate. This work sheds light on production of solar fuels via an efficient hetero-metal oxide strategy.

A New Pathway for CO2 Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode.

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•–) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•– is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.

Charge transfer and orbital reconstruction of non-noble transition metal single-atoms anchored on Ti2CTx-MXenes for highly selective CO2 electrochemical reduction

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti2C-based single-atom electrocatalysts ([email protected]2CTx, TM = V, Cr, Mn, Fe, Co, and Ni) with two different functional groups (T = –O and –S) was designed. The CO2RR catalytic performance was studied using well-defined ab initio calculations. Our results show that the CO2 molecule can be more readily activated on TM @Ti2CO2 than the [email protected]2CS2 surface. Bader charge analysis reveals that the Ti2CO2 substrate is involved in the adsorption reaction, and enough electrons are injected into the 2π*u orbital of CO2, leading to a V-shaped CO2 molecular configuration and partial negative charge distribution. The V-shaped CO2 further reduces the difficulty of the first hydrogenation reaction step. The calculated ΔG of the first hydrogenation reaction on [email protected]2CO2 was significantly lower than that of the [email protected]2CS2 counterpart. However, the subsequent CO2 reduction pathways show that the UL of the potential determining step on [email protected]2CS2 is smaller than that of [email protected]2CO2. Combining the advantages of both [email protected]2CS2 and [email protected]2CO2, we designed a mixed functional group surface with –O and –S to anchor TM atoms. The results show that Cr atoms anchored on the surface of mixed functional groups exhibit high catalytic activity for the selective production of CH4. This study opens an exciting new avenue for the rational design of highly selective MXene-based single-atom CO2RR electrocatalysts.

Enhanced CO2-to-methane photoconversion over carbon nitride via interfacial charge kinetics steering

Serious carrier recombination and limited active sites are the main restrictions on the efficiency of CO2 photoconversion over g-C3N4-based photocatalysts. Herein, a unique tubular C3N4-carbon heterostructure was constructed via thermal polycondensation process, where the inherent open porous C3N4 microstructure was rationally exploited as scaffolds to co-assemble with pyridinic N moieties into composites. Beyond the critical role of serving as a carbon source, the EDTA-2Na additive provides a fairly straightforward pathway for the production of surface cyano groups, which presumably results from the dehydration process of amide bonds. The interfacial cyano groups and work function difference induce strong built-in electric field effects, boosting spatial carrier transfer kinetics. Meanwhile, the incorporated reactive N species endow high affinity for CO2 and thereby remarkable enhancement of uptake capacity. The developed hybrid system modulates the CO2 reduction pathway with favoured 8e− selectivity (56%) toward CH4 products, with an evolution rate up to 2.54 μmol·g-1 h−1, compared with trace of the bare C3N4 counterpart. This work constitutes a prospective target for surface and interface design and paves the way for developing high-performance photocatalysts for multi-electron CO2 reduction.

Sulfur-modified copper synergy with nitrogen-defect sites for the electroreduction of CO2 to formate at low overpotentials

Reducing carbon dioxide to formate is one of the most promising methods to achieve peak carbon dioxide emissions. Nevertheless, the low overpotential in energy conversion remains a major challenge. Herein, a new composite catalyst consisting of cuprous sulfide and graphite-phase carbon nitride with nitrogen defects (Cu2S/NDg-C3N4) is synthesized, which simultaneously achieves a high Faradaic efficiency of 82.3% to formate at a low overpotential of 57 mV. Our studies suggest that electron-rich N defects serve as Lewis basic sites to activate CO2 and increase the local CO2 concentration of active sites, which improves the catalytic activity. The catalyst can spontaneously form a heterojunction by in situ Raman spectroscopy detected during the CO2 reduction process, which improves the electrolysis durability. The *OCHO* species detected by in situ ATR-IR spectroscopy verified the O-end adsorption pathway of CO2 reduction to formate on Cu2S/NDg-C3N4. DFT calculations show that sulfur promotes the activation of interface water, forming hydrogen species that can promote intermediate hydrogenation to *OCHO*, which reduces the overpotential. This work shows lower overpotentials than other reported copper-based catalysts and provides a new strategy for designing a simple and energy-saving CO2 reduction catalyst.