Activity For CO2 Reduction Research Articles

Nonmetallic catalysts with high activity and selectivity for the electrocatalytic reduction of CO2 to CO

The escalating reliance on fossil fuels has intensified CO2 emissions, presenting significant environmental challenges. Electrocatalytic CO2 reduction offers a dual solution by converting CO2 into valuable chemicals, but complex mechanisms limit selectivity and efficiency. This study introduces a nitrogen-doped carbon catalyst, JGNC, synthesized via pyrolysis with predominantly pyrrolic N (8.18% N content). The JGNC catalysts achieved a current density of −770 mA·cm−2 at −1.2 V (V as. RHE) and CO selectivity of 96.55% at −1.1 V (V vs. RHE), surpassing most catalysts. In situ characterizations and theoretical analyses reveal that pyrrolic N lowers the energy barrier for CO2 reduction more effectively than pyridinic and graphitic forms, stabilizing the CO intermediate. These results highlight the potential of pyrrolic N in advancing CO2 reduction technologies, offering promising pathways for developing highly active and selective catalysts.

Highthroughput Screening of CuBi Bimetallic Catalyst Array for Electrocatalytic CO2 Reduction Reaction by Scanning Electrochemical Microscope.

The testing and evaluation of catalysts in CO2 electroreduction is a very tedious process. To study the catalytic system of CO2 reduction more quickly and efficiently, it is necessary to establish a method that can detect multiple catalysts at the same time. Herein, a series of CuBi bimetallic catalysts have been successfully prepared on a single glass carbon electrode by a scanning micropieptte contact method. The application of scanning electrochemical microscopy (SECM) enabled the visualization of the CO2 reduction activity in diverse catalyst micro-points. The SECM imaging with Substrate generation/tip collection (SG/TC) mode was conducted on CuBi bimetallic micro-points, revealing that HER reaction emerged as the prevailing reaction when a low overpotential was employed. While the applied potential was lower than -1.5 V vs. Ag/AgCl, the reduction of CO2 to formic acid became dominant. Increasing the bismuth proportion in the bimetallic catalyst can inhibit the hydrogen evolution reaction at low potential and enhances the selectivity of the CO product at high cathode overpotential. This research offers a novel approach to examining arrays of catalysts for CO2 reduction.

The Positional Effect of an Immobilized Re Tricarbonyl Catalyst for CO2 Reduction.

The storage of renewable energy through the conversion of CO2 to CO provides a viable solution for the intermittent nature of these energy sources. The immobilization of rhenium(I) tricarbonyl molecular complexes is presented through the reductive coupling of bis(diazonium) aryl substituents. The heterogenized complex was characterized through ultra-visible, attenuated total reflectance, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy to probe the electronic structure of the immobilized complex. In addition, studies of cyclic voltammetry, controlled potential electrolysis, and electrochemical impedance spectroscopy were conducted to examine the CO2 reduction activity. The structure and CO2 reduction performance were compared with a previously reported immobilized rhenium(I) tricarbonyl molecular complex to probe the effect of varying the tethering of the aryl substituent from the 5,5'-position to the 4,4'-position of the 2,2'-bipyridine backbone. The immobilized complex on carbon cloth at the 4,4'-position provided excellent selectivity (FECO > 99%) and maximum TONCO and TOFCO values of 3359 and 0.9 s-1, respectively, without the addition of a Bro̷nsted acid source. A nonaqueous flow cell demonstrated the stability of this complex during a 5 h electrolysis. Tethering at the 4,4'-position, compared to the 5,5'-position, yielded lower overall activity for CO2 reduction and was attributed to the difference in growth morphology and formation of aggregations, due to Re-Re dimer formation and π-π stacking interactions within the metallopolymer matrix. For carbon cloth substrates, an optimized catalyst loading was determined to be 44.6 ± 11 nmol/cm2.

Electronic interaction and band alignment between Cu sub-nanometric clusters and ZnIn2S4 nanosheets towards selective photoreduction of CO2 to CO

Engineering the electronic properties of heterogeneous photocatalysts with charge transfer regulated is an effective strategy to boost their CO2 reduction activity. Here, we drew inspiration from the strong metal-support interaction effect, and fabricated ZnIn2S4 supported-Cu sub-nanometric clusters photocatalyst. Within this catalyst, the formed CuS bond would redistribute interfacial charge, resulting in diverse chemical states of Cu atoms and the establishment of Ohmic contact between ZIS and Cu. The built-in electric field of such Ohmic contact benefited the migration of photoexcited electrons from ZIS to Cu. Further mechanistic studies unveiled the crucial role of positively charged Cu atom near the interface in facilitating H2O dissociation, and its adjacent Cu atom at the top-surface adopting a distinct chemical state could activate linear CO2 molecule into a bent configuration. These features substantially lowered energy barriers for CO2 adsorption and subsequent *COOH formation, and Cu-ZIS, accordingly, exhibited a remarkable CO production rate of 60.2 μmol g-1h−1, approximately 20.8-fold enhancement compared to ZIS counterpart.

Synergistic effect between sulfur vacancies and S-scheme heterojunctions in WO3/VS-Zn3In2S6 for enhanced photocatalytic CO2 reduction in H2O vapor

Converting CO2 into CO, CH4, and other hydrocarbons using solar energy presents a viable approach for addressing energy shortages. In this study, photocatalysts with S-deficient WO3/Zn3In2S6 (WO3/VS-ZIS) S-scheme heterojunctions have been successfully synthesized. Under UV–vis light irradiation, 20 %WO3/VS-ZIS demonstrated significantly improved CO2 reduction activity and CH4 selectivity. Detailed characterization and density functional theory (DFT) calculations reveal that the enhanced performance is due to the synergistic optimization of the S-scheme heterojunction and sulfur vacancies (VS) for CO2 reduction. The presence of VS aids in the adsorption and activation of CO2 and enhances the separation of charge carriers. The 2D/2D S-scheme heterostructure assembled with WO3 nanosheets not only accelerates the migration and separation of photoexcited charge carriers but also improves the adsorption of H2O and the formation of VS, thereby increasing the adsorption and activation of CO2 and facilitating the protonation of CO* to produce CH4. This study clarifies the synergistic effect of VS and S-scheme heterostructures in improving photocatalytic performance, offering valuable insights into the photoactivation process of CO2 at VS in S-scheme heterojunctions.

Revealing Real Active Sites in Intricate Grain Boundaries Assemblies on Electroreduction of CO2 to C2+ Products

AbstractAlthough intricate structural assemblies contribute to enhancing the activity of electrocatalytic CO2 reduction (ECR) to C2+ products, blindly coupling multiple design strategies may not yield the expected results, and even inhibit the activity of intrinsic catalytic sites. Therefore, elucidating the promoting or inhibitory effects of each design strategy on the CO2‐to‐C2+ conversion to clarify the real active sites and dynamic oxidation processes is of paramount importance. Here, commonly used grain boundaries (GBs), oxidation states, and alloying strategies are focused on, constructing four different types of catalysts structures: original Cu GBs, oxygen‐enriched grain boundary oxidation (GBO), Ag‐enriched GBO, and Cu/Ag GBs. Multiple operando characterizations reveal that GBs and GBO strengthen the resistance of the oxidative Cu species to the electrochemical reduction. The in situ generated strongly oxidative hydroxyl radicals alter the local reaction environment on the catalyst surface, inducing and stabilizing oxidative Cuδ+ species. Catalytic activity comparisons indicate that the oxidation state of Cu plays a decisive role in the CO2‐to‐C2+ conversion, and the nanoalloy effect tends to favor the CH4 production in intricate GBs assemblies. Theoretical calculations suggest that weak CO adsorption on GBO structures facilitates hydrogenation, promoting C–C coupling toward C2+ products.

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.

Synergistic Effects of the Electric Field Induced by Imidazolium Rotation and Hydrogen Bonding in Electrocatalysis of CO2.

The roles of the ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and water in controlling the mechanism, energetics, and electrocatalytic activity of CO2 reduction to CO on silver in nonaqueous electrolytes were investigated. The first electron transfer occurs to CO2 at reduced overpotentials when it is trapped between the planes of the [EMIM]+ ring and the electrode surface due to cation reorientation as determined from voltammetry, in situ surface-enhanced Raman spectroscopy, and density functional theory calculations. Within this interface, water up to 0.5 M does not induce significant Faradaic activity, opposing the notion of it being a free proton source. Instead, water acts as a hydrogen bond donor, and the proton is sourced from [EMIM]+. Furthermore, this study demonstrates that alcohols with varying acidities tune the hydrogen bonding network in the interfacial microenvironment to lower the energetics required for CO2 reduction. The hydrogen bonding suppresses the formation of inactive carboxylate species, thus preserving the catalytic activity of [EMIM]+. The ability to tune the hydrogen bonding network opens new avenues for advancing IL-mediated electrocatalytic reactions in nonaqueous electrolytes.

Hot Electrons Induced by Localized Surface Plasmon Resonance in Ag/g-C3N4 Schottky Junction for Photothermal Catalytic CO2 Reduction.

Converting carbon dioxide (CO2) into high-value-added chemicals using solar energy is a promising approach to reducing carbon dioxide emissions; however, single photocatalysts suffer from quick the recombination of photogenerated electron-hole pairs and poor photoredox ability. Herein, silver (Ag) nanoparticles featuring with localized surface plasmon resonance (LSPR) are combined with g-C3N4 to form a Schottky junction for photothermal catalytic CO2 reduction. The Ag/g-C3N4 exhibits higher photocatalytic CO2 reduction activity under UV-vis light; the CH4 and CO evolution rates are 10.44 and 88.79 µmol·h-1·g-1, respectively. Enhanced photocatalytic CO2 reduction performances are attributed to efficient hot electron transfer in the Ag/g-C3N4 Schottky junction. LSPR-induced hot electrons from Ag nanoparticles improve the local reaction temperature and promote the separation and transfer of photogenerated electron-hole pairs. The charge carrier transfer route was investigated by in situ irradiated X-ray photoelectron spectroscopy (XPS). The three-dimensional finite-difference time-domain (3D-FDTD) method verified the strong electromagnetic field at the interface between Ag and g-C3N4. The photothermal catalytic CO2 reduction pathway of Ag/g-C3N4 was investigated using in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS). This study examines hot electron transfer in the Ag/g-C3N4 Schottky junction and provides a feasible way to design a plasmonic metal/polymer semiconductor Schottky junction for photothermal catalytic CO2 reduction.

PAN-assisted preparation of Bi2MoO6 with enhanced photocatalytic CO2 reduction performance

In this study, to improve photocatalytic CO2 reduction efficiency of Bi2MoO6-based photocatalysts, Bi2MoO6 (BMO) was synthesized via a solvothermal method with the assistance of polyacrylonitrile (PAN). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were utilized to evaluate the microstructures, phases, and elemental compositions of the samples. Additionally, the separation and migration efficiency of photogenerated charge pairs during the photocatalytic process were analyzed in detail using surface photovoltage spectroscopy (SPS), photoluminescence spectrum (PL), transient photocurrent density (TPR), and electrochemical impedance spectroscopy (EIS). In comparison with the reference sample, the specific surface area of 2 % BMO (mass ratios of PAN/Bi(NO3)3·5H2O is 2 %) has been increased to 39.6 m2/g, which increases by 0.9 times compared to the reference sample. The successful introduction of oxygen vacancies (OVs) in Bi2MoO6 was confirmed by low-temperature electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), and suitable OVs is favorable for separation and migration of the photogenerated carriers. The experimental results indicate that the separation efficiency of photogenerated carriers in the PAN-BMO photocatalyst is significantly boosted in contrast to the reference sample. Furthermore, all photocatalysts exhibit higher photocatalytic CO2 reduction activity than the reference sample. It is noteworthy that the 2 % BMO sample shows the highest photocatalytic CO2 reduction activity, and the average photocatalytic CO2 reduction yield over the 2 % BMO reaches 2.16 μmol g−1 h−1, which is 2.25 times higher than that on the reference sample (0.96 μmol g−1 h−1). In view of the findings, photocatalytic CO2 reduction mechanism for BMO with OVs was rationally proposed.

The cooperative p-n heterojunction and Schottky junction in Au-decorated hierarchical CuS@SnS2 hollow cubes for boosted charge transport and CO2 photoreduction

During the photocatalytic CO2 reduction process, fast charge transport, abundant active sites, and high visible light utilization in photocatalysts are key to achieving excellent CO2 conversion efficiency. In this work, we have designed and prepared hierarchical CuS@SnS2p-n heterostructure hollow cubes for photocatalytic CO2 reduction. First, a monolayer of CuS was in situ generated on the pre-prepared Cu2O cubes to construct core–shell Cu2O@CuS cubes by sulfidation of Cu2O cubes. The following etching process led to the formation of CuS hollow cubes. Finally, the hierarchical CuS@SnS2p-n heterostructure hollow cubes were obtained by growing SnS2 nanosheets on the CuS hollow cubes. The prepared CuS@SnS2p-n heterostructure hollow cubes showed an improved photocatalytic CO2 reduction activity compared with the bare CuS and SnS2 control samples. The p-n heterojunction formed between SnS2 and CuS as well as its hollow structure enhanced the charge carrier separation efficiency and the light absorption capacity of the hybrid catalyst. Furthermore, after the decoration of Au nanoparticles, the formed Schottky junction further discouraged the charge carrier recombination. Thus, the cooperative p-n heterojunction and Schottky junction greatly facilitated photocatalytic CO2 reduction, and exhibiting the maximum CO and CH4 yields of 140.1 and 77.5 μmol g−1 h−1, respectively. This work presents an efficient design of high-performance catalysts for photocatalytic CO2 reduction.

(Invited) Elucidating the Cation Effect in CO2 Electroreduction Using Non-Metal Cations

Electrochemical reduction of CO2 may enable a promising route for the recycling of CO2 and the sustainable production of chemicals and fuels. Due to the complex electrochemical environment, a deeper understanding of the reaction mechanism, particularly the role of cations in the process, is still needed. It was recently demonstrated that metal cations are essential for the CO2 reduction to CO, by stabilizing the CO2 – intermediate via electrostatic interaction. Here we investigate the cation effect in CO2 reduction using non-metal cations, particularly quaternary ammonium cations, whose size and shape symmetry can be tuned. We select CO2 reduction on Bi catalyst that produces both CO and formate, thus to reveal and compare the effect of cations on the two reaction pathways. Interestingly, the Faradaic efficiency for CO production increased apparently for the electrolyte with larger cations, while the formate Faradaic efficiency showed a weak dependence on the cation size, indicating a reaction-pathway-dependent effect of the cations. We further compared cations with different symmetries and observed a more profound effect of substituted ammonium cations on the CO2 reduction activity and selectivity, which was attributed to the charge distribution and weak hydration shells of the cations that help stabilize reaction intermediates. Our work elucidates the critical role of cations in the CO2 electroreduction catalysis and suggests a method to improve the electrocatalysis with optimized electrolytes.

Aggregation of Homogeneous Porphyrin Catalysts in Organic Electrolyte Broadly Inhibits Electrochemical CO2 Reduction Performance

Metalloporphyrins are widely used as homogeneous electrocatalysts for the production of renewable fuels from abundant feedstocks and sustainable energy. The modularity of porphyrin catalysts has led to the establishment of structure‐function correlations that aid in predicting and optimizing catalytic activity. Although metalloporphyrins are widely known to aggregate due to their planar structure that promotes π–π stacking, it is surprising that the influence of metalloporphyrin aggregation on electrocatalytic performance has not been previously investigated. Herein, we will document the relative aggregation and electrocatalytic activity for CO2 reduction to CO with three structurally related iron meso-phenylporphyrins in commonly used N,N-dimethylformamide (DMF) electrolyte. An inverse dependence of kinetics on catalyst concentration is observed for all three porphyrins based on cyclic voltammetry data. Furthermore, this inhibition extends to bulk electrolysis performance, where up to 75% of the catalyst in a 1 mM solution is inactive compared to in a 0.25 mM solution. This talk will additionally discuss how aggregation is influenced by organic additives, axial ligands, redox state, metal identity, and porphyrin substituents. Overall, this work emphasizes that metalloporphyrins can aggregate severely (even in well-solubilizing organic electrolytes) and that aggregation effects must be considered for optimization of performance and for meaningful catalytic activity comparisons.

Atomic Layer Deposition of Cu Catalysts on Gas Diffusion Electrodes for Electrochemical CO2 Reduction

Electrochemical CO2 conversion is gaining attention as an important process for carbon fixation through the use of renewable electricity to address the climate change crisis. Copper is a unique single-element catalyst that can induce C-C coupling reactions to generate high-value-added compounds. The triple phase boundary has been successfully controlled at the catalyst interface using gas diffusion electrodes (GDEs) over the past few years, resulting in high C-C coupling performance. Therefore, methods to engineer the catalyst interface on the 3D structure of GDE are of significant importance. Generally, the catalyst on the GDE is introduced through physical vaper deposition (PVD) using sputtering or E-beam evaporation, or through solution methods such as spray coating and drop-casting of nano-particles. However, the porous and tortuous 3D structure of the GDE often result in limited conformality and difficulty in obtaining a uniform and controlled infiltration of the catalyst into the support structure.In this study, we synthesized Cu catalysts directly onto GDE surfaces using plasma-enhanced atomic layer deposition (PE-ALD), which allowed for precise tuning of the catalyst size and loading at the nanoscale [1]. The synthesized catalysts were confirmed to be polycrystalline Cu nanoparticles using grazing incidence X-ray diffraction. To demonstrate the advantages of the conformal and tunable control of PE-ALD deposition, we deposited the same areal mass loading of Cu catalyst onto the GDE substrates using PVD, and compared the CO2 reduction activity in an H-cell environment. The PE-ALD Cu catalyst showed more than 3 times higher current density than the PVD catalyst at the same electrode potential, a low (~10%) Faradaic efficiency (FE) for the hydrogen evolution reaction (HER), and greater than 75% FE for C-C coupling to form C2+ products including ethylene and ethanol, which is comparable to the highest performances reported to date for metallic Cu catalysts in a H-cell environment. Furthermore, stable operation was observed for a duration of 15 hours, with minimal changes in activity and selectivity. In conclusion, the introduction of catalysts using PE-ALD on GDE electrodes represents a powerful new synthesis method that can increase both C-C coupling performance and selectivity compared to PVD deposition, due to its adjustable Cu nanoparticle size and high conformality. Reference 1) J. D. Lenef, S.Y. Lee, K. M. Fuelling, K. E. Rivera Cruz, A. Prajapati, D. O. D. Cornejo, T. H. Cho, K. Sun, E. Alvarado, T. S. Arthur, C. A. Roberts, C. Hahn, C. C. L. McCrory, N. P. Dasgupta, Nano Lett. 23, 10779-10787 (2023)

Diiron Complexes with Rigid and Conjugated S-to-S Bridges for Electrocatalytic Reduction of CO2.

Electroreduction of CO2 to value-added low-carbon chemicals is a promising way for carbon neutrality and CO2 utilization. It was found that the diiron complex [(μ-bdt)Fe2(CO)6] (bdt = benzene-1,2-dithiolate) has high catalytic activity for electrocatalytic CO2 reduction. To further study the effect of the S-to-S bridge on the catalytic performances of diiron complexes for electrochemical CO2 reduction, four diiron complexes 1-4 with different rigid and conjugated S-to-S bridges were either selected or designed. The electrocatalytic studies showed that under optimal conditions, 2 with a 2,3-naphthalenedithiolato bridge exhibited the lowest catalytic onset potential (Eonset = -1.75 V vs Fc+/0), while 4 with a diphenyl-1,2-vinylidene bridge displayed the highest catalytic activity (TOFmax = 295 s-1), which is 1.5 times that of [(μ-bdt)Fe2(CO)6]. The controlled potential electrolysis experiments of 4 in 0.1 M MeOH/MeCN at -2.35 V vs Fc+/0 gave a total faradaic yield close to 100%, with selectivities of 77%, 9%, and 14% for HCOOH, CO, and H2, respectively. The mechanism for CO2 reduction was studied using density functional theory, IR spectroelectrochemistry, and electrochemical methods. The results indicate that modifying the structure of the S-to-S bridge is an effective strategy to improve the catalytic performance of diiron complexes for electrocatalytic CO2 reduction.

Control interfacial charge transfer behavior by creating surface defects on structure unit of heterojunction to drive carrier separation for enhancing photocatalytic CO2 reduction

Controlling interfacial charge transfer behavior of heterojunction is an arduous issue to efficiently drive separation of photogenerated carriers for improving the photocatalytic activity. Herein, the interface charge transfer behavior is effectively controlled by fabricating an unparalleled VO-NiWO4/PCN heterojunction that is prepared by encapsulating NiWO4 nanoparticles rich in surface oxygen vacancies (VO-NiWO4) in the mesoporous polymeric carbon nitride (PCN) nanosheets. Experimental and theoretical investigations show that, differing with the traditional p-n junction, the direction of built-in electric field between p-type NiWO4 and n-type PCN is reversed interestingly. The strongly codirectional built-in electric field is also produced between the surface defect region and inside of VO-NiWO4 besides in the space charge region, the dual drive effect of which forcefully propels interface charge transfer through triggering Z-Scheme mechanism, thus significantly improving the separation efficiency of photogenerated carriers. Moreover, the unique mesoporous encapsulation structure of VO-NiWO4/PCN heterostructure can not only afford the confinement effect to improve the reaction kinetics and specificity in the CO2 reduction to CO, but also significantly reduce mass transfer resistance of molecular diffusion towards the reaction sites. Therefore, the VO-NiWO4/PCN heterostructure demonstrates the preeminent activity, stability and reusability for photocatalytic CO2 reduction to CO reaction. The average evolution rate of CO over the optimal 10 %-VO-NiWO4/PCN composite reaches around 2.5 and 1.8 times higher than that of individual PCN and VO-NiWO4, respectively. This work contributes a fresh design approach of interface structure in the heterojunction to control charge transfer behaviors and thus improve the photocatalytic performance.

Amorphizing MnIn2S4 Atomic Layers Create an Asymmetrical InO1S5 Polarization Plane for Photocatalytic Ammonia Synthesis and CO2 Reduction.

Building a polarization center is an effective avenue to boost charge separation and molecular activation in photocatalysis. However, a limited number of polarization centers are usually created. Here, a polarization plane based on two-dimensional (2D) atomic layers is designed to maximize the surface polarization centers. The Mn in a 2D crystal lattice is etched from the MnIn2S4 atomic layers to build a consecutive symmetry-breaking structure of isolated InO1S5 sites. More charges aggregate around O, making the isolated InO1S5 sites highly polarized. Due to the formation of the InO1S5 polarization plane, an enormous polarized electric field is formed perpendicular to the 2D atomic layers and the carrier lifetime can be prolonged from 93.2 ps in MnIn2S4 to 1130 ps in amorphous MnxIn2Sy. Meantime, the formed large charge density gradient favors coupling and activation of small molecules. Benefiting from these features, a good NH3 photosynthesis performance (515.8 μmol g-1 h-1) can be realized over amorphous MnxIn2Sy, roughly 2.5 and 48.9 times higher than those of MnIn2S4 atomic layers and bulk MnIn2S4, respectively. The apparent quantum yields reach 5.4 and 3.3% at 380 and 400 nm, respectively. Meanwhile, a greatly improved CO2 reduction activity is also achieved over MnxIn2Sy. This strategy provides an accessible pathway for designing an asymmetrical polarization plane to motivate photocatalysis optimization.

Activity and Selectivity in the Electrochemical Reduction of CO2 at CuSnx Electrocatalysts Using a Zero-Gap Membrane Electrode Assembly

In this study Cu, Sn, and bimetallic CuSnx nanoparticles were synthesized and evaluated as electrocatalysts for CO2 reduction using zero gap membrane electrode assemblies. Results show bimetallic electrocatalysts with Sn contents above 10% yield formate as a primary product with Faradaic Efficiencies near 70% at 350 mA cm−2. Cu-Snx electrocatalysts with less than 10% Sn yield CO at current densities below 350 mA cm−2 and relatively lower cell potentials. When the low-Sn content bimetallic electrocatalysts were evaluated in alkaline anolytes at 350 mA cm−2, ethanol was recorded as the primary product (FE = 48.5% at Ecell ≥ 3.0 V). We propose enhanced C2 activity and selectivity originate from Cu dimers adjacent to Sn atoms for bimetallic electrocatalyst with low-Sn content. The C2 active sites are lost when the surface Sn content exceeds 25%–38%.

One-pot hydrothermal synthesis of transition metal sulfides-decorated CuS microflower-like structures for electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) to value-added products is regarded as a sustainable strategy to mitigate global warming and energy crisis, and designing highly efficient and robust catalysts is essential. In this work, transition metal sulfides (TMS)-decorated CuS microflower-like structures were prepared via the one-pot hydrothermal synthesis method for ECR to CO, and the influence of TMS doping on ECR performance was demonstrated. Characterization of the catalysts was performed using XRD, FESEM-EDS, N2 physisorption, and XPS, revealing the successful loading of TMS, the formation of microflower-like architectures and the generation of sulfur vacancies. Electrochemical tests demonstrated that doping ZnS, Bi2S3, CdS and MoS2 improved the intrinsic CO2 reduction activity of the CuS catalyst. Particularly, the MoS2-CuS composite catalyst with imperfect petal-like structure showed uniform distribution of edge Mo sites, which worked synergistically with the formed grain boundaries (GBs) and undercoordinated S vacancy sites in promoting CO2 activation, stabilizing *COOH adsorption, facilitating *CO desorption, and lowering the energy barrier of the potential-limiting step for improved CO selectivity. The MoS2-CuS catalyst achieved a maximum CO selectivity of 83.2% at –0.6 V versus the reversible hydrogen electrode (RHE) and a high CO cathodic energetic efficiency of 100%. At this potential, the catalyst maintained stable catalytic activity and CO selectivity during a 333-min electrolysis process. The findings will offer a promising avenue for the development of efficient and stable catalysts for CO production from ECR.

Impact of copper on activity, selectivity, and deactivation in the photocatalytic reduction of CO2 over TiO2

The photocatalytic reduction of CO2 to hydrocarbons may be a promising mechanistic route to reduce greenhouse gas CO2, convert it into useful products, and limit the direct emission of CO2. The photocatalytic reduction of CO2 is a reaction in which photons activate the photocatalyst by generating reduced and oxidized sites, that are re-oxidized and re-reduced by the reactants. The photocatalytic reduction of CO2 can produce various products, including CO, formic acid, formaldehyde, methanol, methane, etc.Here, the activity/selectivity of produced hydrocarbons in the presence of oxygen on various photocatalysts (TiO2, 5 wt%Cu-TiO2, 5 wt%Cu-C-TiO2) was determined.The reaction rate increased with increasing reaction time up to the first half an hour of the reaction but then started to decrease with photocatalysts, indicating photocatalyst deactivation, a rate-limiting step by hydroxyl radicals and adsorption of intermediates on TiO2. Carbon deposition as the origin of photocatalyst deactivation was confirmed using the TGA of the spent photocatalyst. Additionally, absorption of intermediates on spent catalysts were confirmed by FTIR. On the other hand, the conversion increased with time when copper was used as a promoter on a TiO2 compared with TiO2 due to its larger surface area and having more active sites.The photocatalysts were characterized using BET, ICP-OES, XRD, TGA, XPS, Fourier-Transform Infrared Spectroscopy (FTIR), and UV–Vis. The focus of this study was to determine the activity and efficacy of different photocatalysts (TiO2, 5 wt%Cu-TiO2, 5 wt%Cu-C-TiO2) by gas phase measurement, with a particular emphasis on obtaining reproducible data on conversion and selectivity as a function of irradiation time.The copper on TiO2 was found to be more selective towards sodium formate/formic acid with a maximum selectivity of ∼90 % in 4 h and had higher activity (74.3 µmol gcat-1 h-1). A maximum CO with a selectivity of 86 % was found when TiO2 was used in 4 h.Copper transfer electrons on the TiO2 surface enhance CO2 adsorption on the catalytic surface and is the reason for having higher valuable product on Cu-C-TiO2 and Cu-TiO2 compared with TiO2. Carbon in this experiment did not have a role and its effect was negligible.