Activity For CO2 Reduction Research Articles

TM@MoSSe (TM = Ni, Fe) as novel electrocatalysts for reduction of CO2 to CO: A DFT study

It is crucial to develop highly efficient, selective and low-overpotential electrocatalysts for CO2 reduction. This paper proposes an efficient iron and nickel single-atom catalyst using Janus MoSSe as the substrate to reduce CO2 to CO by using DFT calculations. The adsorption of a single TM atom like Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt on Janus MoSSe monolayer results in a decrease in band gap, which may accelerate the catalytic CO2 reduction. The excellent catalytic activity of Fe@MoSSe and Ni@MoSSe is owing to the high d-band center and hence the strong TM-CO2 bonding. The asymmetric structure of Janus MoSSe creates the local built-in electric field, which further increases by about 8% or 0.8% after the adsorption of single Ni or Fe atom so as to afford the better electrocatalytic performances for reduction of CO2 to CO in both TM modified systems. So, this work proposes the catalysts Fe@MoSSe and Ni@MoSSe with good selectivity and activity for CO2 reduction by revealing their underlying mechanisms, and Janus MoSSe may be used as a potential substrate material for CO2 reduction catalysts.

CO2 Reduction by Transition‐Metal Complex Systems: Effect of Hydrogen Bonding on the Second Coordination Sphere

AbstractHomogeneous electrocatalysts typified by transition‐metal complex show transcendent potency in efficient energy catalysis through molecular design. For example, metal complexes with elaborate design performed wonderful activity and selectivity for electrocatalytic CO2 reduction. Primary coordination sphere of metal complexes plays a key role in regulating its intrinsic redox properties and catalytic activity. However, the overall reduction efficiency of CO2 is also bound up with the substrate activation process. Transition‐metal complexes are hoped to exhibit reasonable redox potential, reactive activity, and stability, while binding and activating CO2 molecules to achieve efficient CO2 reduction. Construction of second coordination sphere, especially hydrogen‐bonding network of transition‐metal complexes, is reported to be the “kill two birds with one stone” strategy to realize efficient CO2 reduction catalysis via systematic catalyst properties modulation and substrate activation. Herein, we present recent progress on the construction of hydrogen‐bonding network in the second coordination sphere of metal complexes by ligand modification or the introduction of exogenous organic ligand, and the resulted productive enhancement of the catalytic performance of metal complexes by the improvement of adsorption capacity and activation of CO2, proton transfer rate, and stability of reaction intermediates, and so forth.

Hydrogen- assisted synthesis of defective triazine/heptazine homostructured nanosheets for efficient CO2photoreduction.

Homostructure construction has been demonstrated to be an effective way for boosting the photocatalytic activity of polymeric carbon nitride. However, the contribution of the intrinsic activity of molecular fragments in the catalytic performance of homostructured carbon nitride is yet to be explored. In this paper, a facile hydrogen-assisted strategy was used to synthesize triazine/heptazine intermolecular homojunctions (g-C3N4(MU-H)) with an ultrathin and defective structure, via the co-pyrolysis of melamine and urea precursors. Experimental characterizations and theoretical calculations revealed the copolymerization of triazine- and heptazine-based carbon nitride generated a homostructured interface with a large build-in electric field for efficient separation of photogenerated carriers. Due to the synergestic effect between the homostructured interface and nitrogen vacancies, as-synethesized g-C3N4(MU-H) exhibited an outstanding activity for photocatalytic CO2 reduction, with a CO yield rate of 14.45 μmol h-1, which was 23.5 and 3.64 times higher than those of bulk g-C3N4 and g-C3N4(M-H) synthesized from a single precursor, respectively. This study provides a new avenue for optimizing the charge separation efficiency of CO2 photoreduction catalysts by constructing intramolecular homojunction.

In-situ imaging and time-resolved investigation of local pH in electrocatalytic CO2 reduction

Local pH near the catalyst surface exerts a substantial influence on both catalytic selectivity and activity in electrocatalytic CO2 reduction (CO2RR). While the investigation of local pH remains challenging in the aspect of in-situ imaging and monitoring. In this study, a novel lateral-type surface-enhanced Raman spectroscopy (L-SERS) system with a wide pH testing range from acidic to alkaline, is developed for the in-situ observation of local pH distributions with high spatial and temporal resolution during CO2RR. Excellent in-situ imaging of local pH near the catalyst surface is obtained, showing good consistency with simulation results. Besides, the gradual pH elevation and stabilization can be monitored via this time-resolved local pH investigation. This study presents a direct visualization of local pH distribution and variation at the Nernst layer during CO2RR, providing direct evidence in local pH for the feasibility of acidic electrolyte and offering theoretical guidance for optimizing CO2RR conditions.

Pb-N Chemically Anchors CsPbBr3 on 1D Porous Tubular g-C3N4 for Enhanced Photocatalytic CO2 Reduction.

Halide perovskite CsPbBr3 (CPB) quantum dots (QDs) are considered as a promising candidate for solar-driven CO2 conversion for their unique optoelectronic properties and suitable band structure. However, the CO2 conversion efficiency of pristine CsPbBr3 quantum dots is severely limited due to their rapid electron-hole pair recombination and insufficient active sites. In this study, by immobilizing CPB QDs onto one-dimensional (1D) porous tubular g-C3N4 (TCN), an effective 0D/1D CPB@TCN heterojunction photocatalyst for CO2 reduction is fabricated. Density functional theory (DFT) calculations combined with experimental studies demonstrate that CPB QDs are uniformly anchored on the surface of TCN through Pb-N chemical bonding, resulting in efficient separation and transfer of photogenerated carriers in CPB@TCN photocatalysts. The resultant CPB@TCN photocatalysts exhibit significantly enhanced photocatalytic activity for CO2 reduction with the highest conversion rate of 22.62 μmol·g-1·h-1, which is 5.33-times higher than that of pristine CPB QDs. This work unveils the interfacial bonding mechanism of CPB@TCN heterojunction through Pb-N chemical bond, which provides new insights for the development perovskite-based heterojunction photocatalysts.

Tannic Acid Selective Modulation Defects to Enhance the Photocatalytic CO2 Reduction Activity of Layered Double Hydroxides.

Recently, layered double hydroxides (LDH) have shown great potential in photoreduction of CO2 owing to its flexible structural adjustability. In this study, the mild acidic property of tannic acid (TA) is exploited to etch the bimetal LDH to create abundant vacancies to gain the coordination unsaturated active centers. Based on the different chelating abilities of TA to various metal ions, the active metals are remained by selective chelation while the inert metals are removed during the etching process of bimetal LDH. Furthermore, selective chelating with metal ions not only increases the percentage of highly active metals but also compensates for the structural damage caused by the etch, which achieves a scalpel-like selective construction of vacancies. The NiAl-LDH etched and functionalized by TA for 3h exhibits superior photo-reduction of CO2 performance without co-catalysts and photo-sensitizers, which is 14 times that of the pristine NiAl-LDH. The fact that many bimetal LDHs can be functionalized by TA and exhibit significantly improved photocatalytic efficiency is confirmed, suggesting this strategy is generalized to functionalize double- or multi-metal LDH. The method provided in this work opens the door for polyphenol-functionalized LDHs to enhance their ability for light-driven chemical transformations.

Enhanced Ferroelectric Polarization in Au@BaTiO3 Yolk-in-Shell Nanostructure for Synergistic Boosting Visible-Light- Piezocatalytic CO2 Reduction.

Developing efficient photo-piezocatalytic systems to achieve the conversion of renewable energy to chemical energy emerges enormous potential. However, poor catalytic efficiency remains a significant obstacle to future practical applications. Herein, a series of unique Au@BaTiO3 (Au@BT) yolk-shell nanostructure photo-piezocatalyst is constructed with single Au nanoparticle (Au NP) embedded in different positions within ferroelectric BaTiO3 hollow nanosphere (BT-HNS). This special structure showcases excellent mechanical force sensitivity and provides ample plasmon-induced interfacial charge-transfer pathways. In addition, the powerful piezoelectric polarization electric field induced by the enhanced ferroelectric polarization electric field via corona poling treatment in BT-HNS further promotes charge separation, CO2 adsorption and key intermediate conversion. Notably, BT with single Au NP encapsulated into hollow nanosphere shell with reinforced polarization (Au@BT-1-P) shows synergistically improved photo-piezocatalytic CO2 reduction activity for producing CO with a high production rate of 31.29 µmol g-1 h-1 under visible light irradiation and ultrasonic vibration. This work highlights a generic tactic for optimized design of high-performance and multifunctional nanostructured photo-piezocatalyst. Meanwhile, these yolk-in-shell nanostructures with single Au nanoparticle as an ideal model may hold great promise to inspire in-depth exploration of carrier dynamics and mechanistic understanding of the catalytic reaction.

Enhanced photoelectrochemical CO2 reduction activity towards selective generation of alcohols over CuxO/SrTiO3 heterojunction photocathodes

Photoelectrochemical reduction (PECR) of CO2 to value-added chemicals and fuels will reduce the dependency on fossil fuels, also it will solve environmental issues that arise due to greenhouse gases. A heterojunction of CuxO/SrTiO3 with varying post-annealing temperature ranges from 300 to 600 °C (CS300-600) was synthesized by overlying the spin-coated SrTiO3 on electrodeposited Cu2O over the FTO glass substrate. The synthesized photoelectrode's crystallinity and phase formation significantly varied by varying the post-annealing temperature, which was characterized via XRD and Raman spectroscopy. Optical, morphological, type of heterojunction formation and elemental surface oxidation states of photoelectrodes were studied through UV–visible DRS spectrum, FE-SEM, and XPS analysis respectively. Electrocatalytic analysis such as Linear Sweep Voltammetry (LSV), and Electrochemical Impedance Spectrometry (EIS) was employed, thus it conforms to the highest photocurrent density (−1.38 mA/cm2 at −0.6V vs. Ag/AgCl), and low charge transfer resistance (RCT=0.412 kΩ) at the electrode-electrolyte interfaces for CS500 photoelectrode as compared to others photoelectrodes. PECR of CO2 to liquid product formation was evaluated by applying different potential ranges (0 to −0.6 V vs. Ag/AgCl). Highest methanol formation of 48.69 μmol.cm−2hr−1, which is approximately 9 times enhanced as compared to the pure Cu2O (5.62 μmol.cm−2hr−1) photoelectrode at 0 V vs Ag/AgCl for CS500 heterojunction. Optimization of overlaying SrTiO3 synthesis temperature for crystallization formation on Cu2O and applied photoelectrode potential findings could pave the way for designing other new heterojunction types for selective liquid alcohol production.

CO2 photoreduction using encapsulated potassium bismuth iodide (K3Bi2I9) perovskite in porous supports

Lead-free halide perovskites (LFHP) are one of the most promising materials for CO2 photoreduction; however, their stability is an issue that must be solved to scale up the manufacturing. To overcome this limitation, this work proposes the encapsulation of LFHP of K3Bi2I9 in three inorganic supports based on aluminosilicates such as (i) geopolymer, (ii) tobermorite, and other based on (iii) magnesium oxychloride. These supports provide a porous structure and active sites to host the perovskite particles, which favor enhanced light absorption, stability, and their activity for CO2 reduction under visible light. The encapsulated perovskites exhibited activity to photoconvert CO2 into formic acid (HCOOH) with efficiencies up to 2500 μmol h−1 using the K3Bi2I9 host in geopolymer. This support provides stable polysialate-diloxo chains to encapsulate the perovskite, delayed the degradation in aqueous medium, and its activity was demonstrated during 16 h of continuous visible light irradiation. The good stability and efficiency for CO2 reduction was associated to the formation of K3Bi2I9/BiOI heterojunction that prevent the degradation of the structure and enhance the charge transfer between both semiconductors.

Effect of Cu/Bi ratio on the photoelectrochemical performance of CuBi2O4/CuO nanocomposite films for CO2 reduction

Abstract Solar energy is free, clean, and virtually limitless; however, its conversion into a storable form presents technological challenges. One avenue towards solar energy utilization is the photoelectrochemical (PEC) reduction of CO2 to one- or two-carbon fuels, employing a semiconductor configured as an electrode. A potential material for this application is the p-type copper bismuth oxide (CuBi2O4) with a band gap capable of visible light absorption and a conduction band edge position suitable for CO2 reduction. In this study, CuBi2O4 nanocomposite films of varying Cu/Bi ratios (0.25, 0.51, 0.68, 0.94, 2.04) were prepared via an electrodeposition-spray deposition-annealing route. Where the Cu/Bi ratio exceeded the stoichiometric value of 0.5, a bilayered film composed of a copper (II) oxide (CuO) phase on top of CuBi2O4 was formed, creating a planar heterojunction between the two oxide layers. With increasing Cu/Bi ratio, the light absorption range of the films broadened due to the CuO phase. Analysis of the photocurrent-potential behavior of the films under visible-light illumination showed a 4–7-fold increase in the photocurrent from an inert electrolyte to a CO2-saturated electrolyte, confirming potential activity for CO2 reduction of the CuBi2O4/CuO films. A higher Cu/Bi ratio resulted to an improved charge separation efficiency, enhancing the photocurrent generation. However, the transient photocurrent response of the films showed a 70-80% decrease in the photocurrent after only 15 mins of testing. When tested in an electrolyte with an electron scavenger, the percent decrease was lowered to <10%, indicating that the instability of the films resulted from poor interfacial kinetics. While the CuBi2O4/CuO nanocomposite films can accomplish CO2 reduction, further strategies to improve their efficiency and stability are needed to realize practical application.

Studying bimetals copper-indium for enhancing PCN photocatalytic CO2 reduction activity and selectivity mechanism

In this work, a bimetallic indium-copper-doped atomically dispersed Cu-In-PCN photocatalyst was prepared by thermal polymerization, and it exhibits remarkable photocatalytic CO2 reduction activity with CO yield of 113.56 µmol g−1 and a selectivity nearly 96 %. Additionally, experimental investigations and DFT calculations reveal the mechanisms underpinning the high performance of Cu-In-PCN catalyst, that Cu 3d and In 5p orbitals contribute to the band composition of Cu-In-PCN and reduced the bandgap, the electrons from PCN transfer to copper active sites and increasing the electron density for CO2 reduction. Furthermore, the Cu-In bimetallic lowered the free energy of COOH* intermediate, which more easily conversion to CO via dehydroxylation than PCN, Cu-PCN, and In-PCN. In situ FTIR show that the COOH* is the key intermediate in the photocatalytic reduction of CO2 to CO. This work makes up for the current shortcomings of using bimetallic-doped PCN for photocatalytic CO2 with low selectivity and unclear mechanism.

Z-scheme ZnIn2S4/CuxO heterostructure on flexible substrate for efficient photothermal catalytic CO2 reduction

The ZnIn2S4 nanosheets were successfully synthesized on the surface of compacted stainless steel mesh using a simple solvothermal method, and further modified with CuxO nanoparticles to form ZnIn2S4/CuxO heterojunction photocatalyst via a wet chemistry approach. These photocatalysts were then utilized for photothermal catalytic CO2 reduction under full spectrum solar light. The experimental results demonstrated that the deposition of the photocatalyst on the flexible substrate effectively prevented the aggregation of ZnIn2S4 nanosheets. The incorporation of CuxO nanoparticles enhanced the specific surface area of the photocatalyst, and created a Z-scheme heterojunction with ZnIn2S4 to improve the utilization efficiency of photogenerated electrons. It was noteworthy that the dark red CuxO exhibited a full spectrum response and excellent photothermal effect, thereby facilitating carrier migration and reducing CO2 catalytic reaction barriers. Consequently, the optimized ZnIn2S4/CuxO exhibited significantly enhanced CO2 to CO yield of 1515.8 μmol m-2h−1 and CH4 yield of 1579.4 μmol m-2h−1, which was about 7.5 and 7.6 times higher than those achieved by pure ZnIn2S4, respectively. Furthermore, this study provided detailed insights into the mechanism of photocatalytic CO2 reduction over composite material as well as valuable guidance for designing immobilized photocatalysts with high activity for CO2 reduction.

Efficient photocatalytic CO2 and Cr(VI) reduction on carbon spheres/g-C3N4 composites with enriched nitrogen vacancies

In this study, carbon spheres (CS)/g-C3N4 composite materials were fabricated by a hydrothermal method, and the characterizations have confirmed the successful anchoring of CS onto the surface of g-C3N4, constructing enriched nitrogen vacancies during the synthesis process. The photocatalytic CO2 reduction activity of g-C3N4 is enhanced by all of these advantageous factors. The significant enhancement can be attributed to the tight interfacial interaction between CS and g-C3N4, which endows with the photocatalyst a larger specific surface area, higher light utilization efficiency and stronger capability for photoinduced charges separation. Furthermore, the presence of nitrogen vacancies further accelerates the separation and migration efficiency of photogenerated charges, provides additional active sites to promote the adsorption and activation of CO2 molecules, thereby effectively boosting the photocatalytic activity for CO2 reduction. The CO2 conversion rate on CS/g-C3N4 composite materials is higher than that on the reference g-C3N4. The apparent quantum yield (AQY) is also superior to that of the reference g-C3N4 under three different monochromatic light irradiations. The stability of the catalyst was verified through cycling experiments, indicating promising potential practical industrial application. The CO2 reduction mechanism and transformation pathways were elucidated using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The photocatalytic reduction rate constant of Cr(VI) by 50CS/CN is 2.9 times higher than that by CN. This study introduces a facile approach for synthesizing g-C3N4-based photocatalytic materials, providing an interesting strategy to boost photocatalytic activity of g-C3N4 for photocatalytic CO2 and Cr(VI) reduction.

Atmosphere engineering of metal-free Te/C3N4 p-n heterojunction for nearly 100% photocatalytic converting CO2 to CO

Carbon nitride (CN)-based heterojunction photocatalysts hold promise for efficient carbon dioxide (CO2) reduction. However, suboptimal production yields and limited selectivity in CO2 conversion pose significant barriers to achieving efficient CO2 conversion. Here, we present the construction of a p-n heterojunction between ultrasmall Te NPs and CN nanosheet using a novel tandem hydrothermal-calcination synthesis strategy. Through ammonia-assisted calcination, ultrasmall Te NPs are grown in-situ on the CN nanosheets’ surface, resulting in the generation of a robust p-n heterojunction. The synthesized heterojunction exhibits increased specific surface area, reinforced visible light absorption, intensive CO2 adsorption capacity, and efficient charge transfer. The optimum Te/CN-NH3 demonstrates superior photocatalytic CO2 reduction activity and durability, with nearly 100 ​% selectivity for CO and a yield as high as 92.0 ​μmol ​g−1 ​h−1, a fourfold increase compared to pure CN. Experimental and theoretical calculations unravel that the strong built-in electric field of the Te/CN-NH3 p-n heterojunction accelerates the migration of photogenerated electrons from Te NPs to the N site on CN nanosheets, thereby promoting CO2 reduction. This study provides a promising material design approach for the construction of high-performance p-n heterojunction photocatalysts.

Thiacalix[4]arene-Stabilized Sb/Ag Bimetallic Nanoclusters: Elucidating the Effects of Sb Doping on Electrocatalytic CO2 Reduction in Ag Clusters.

Accurately identifying the metal doping effects within heterogeneous catalysts presents a formidable challenge due to the complex nature of controlling the interfacial chemistry at the molecular level. Herein, we use two sets of atomically precise nanoclusters to demonstrate the impact of Sb doping on the electrocatalytic CO2 reduction activity in Ag nanoclusters. Leveraging the unique properties of the thiacalix[4]arene, we have pioneered a methodology for incorporating catalytic Ag1+ and Sb3+ sites, culminating in the synthesis of the pioneering Sb-Ag bimetallic cluster, Sb2Ag11. We refined this structure by replacing the two Sb3+ sites with Na+ sites, resulting in a Na2Ag10 cluster. Broadening our investigative scope, we isolated the core components from both Sb2Ag11 and Na2Ag10 and obtained two clusters: Sb2Ag4 and Ag4. The subtle compositional variations between two pairs of structurally analogous clusters, Sb2Ag11 and Na2Ag10, as well as Sb2Ag4 and Ag4, create opportunities to investigate how the Sb doping impacts the catalytic activity of Ag clusters. Clearly, compared to the undoped clusters, those doped with Sb exhibit higher catalytic current densities and enhanced CO selectivity. The theoretical calculations suggest that Sb doping can enhance the adsorption barrier of *H, thereby inhibiting hydrogen evolution activity and conversely promoting eCO2RR to CO activity.

Tuning the Inter‐Metal Interaction between Ni and Fe Atoms in Dual‐Atom Catalysts to Boost CO2 Electroreduction

AbstractDual‐atom catalysts (DACs) are promising for applications in electrochemical CO2 reduction due to the enhanced flexibility of the catalytic sites and the synergistic effect between dual atoms. However, precisely controlling the atomic distance and identifying the dual‐atom configuration of DACs to optimize the catalytic performance remains a challenge. Here, the Ni and Fe atomic pairs were constructed on nitrogen‐doped carbon support in three different configurations: NiFe‐isolate, NiFe‐N bridge, and NiFe‐bonding. It was found that the NiFe‐N bridge catalyst with NiN4 and FeN4 sharing two N atoms exhibited superior CO2 reduction activity and promising stability when compared to the NiFe‐isolate and NiFe‐bonding catalysts. A series of characterizations and density functional theory calculations suggested that the N‐bridged NiFe sites with an appropriate distance between Ni and Fe atoms can exert a more pronounced synergy. It not only regulated the suitable adsorption strength for the *COOH intermediate but also promoted the desorption of *CO, thus accelerating the CO2 electroreduction to CO. This work provides an important implication for the enhancement of catalysis by the tailoring of the coordination structure of DACs, with the identification of distance effect between neighboring dual atoms.

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Photoelectrocatalytic CO2 Reduction to Formate Using a BiVO4/ZIF‐8 Heterojunction

Converting CO2 into high‐value chemical fuels through green photoelectrocatalytic reaction path is considered as a potential strategy to solve energy and environmental problems. In this work, BiVO4/ZIF‐8 heterojunctions are prepared by in‐situ synthesis of ZIF‐8 nanocrystals with unique pore structure on the surface of BiVO4. The experimental results show that the silkworm pupa‐like BiVO4 is successfully combined with porous ZIF‐8, and the introduction of ZIF‐8 can provide more sites for CO2 capture. The optimal composite ratio of 4:1‐BiVO4/ZIF‐8 showed excellent CO2 reduction activity and the lowest electrochemical transport resistance. In the electrocatalytic system, 4:1‐BiVO4/ZIF‐8 exhibits formate Faraday efficiency of 82.60% at −1.0 V vs. RHE. Furthermore, the Faraday efficiency increases to 91.24% at − 0.9 V vs. RHE in the photoelectrocatalytic system, which is 10.8 times that of pristine BiVO4. The results show that photoelectric synergism can not only reduce energy consumption, but also improve the Faraday efficiency of formate. In addition, the current density did not decrease during 34 h electrolysis, showing long‐term stability. This work highlights the importance of the construction of heterojunction to improve the performance of photoelectrocatalytic CO2 reduction.

Constructing functionalized carbon quantum dots on amino-rich graphitic carbon nitride to enhance CO2 photocatalytic reduction: Critical role of functional group modulation

Carbon quantum dots (CQDs) decoration have been widely acknowledged as promising strategy in photocatalysis, yet in-depth understanding of the effect of different functionalized CQDs on CO2 photocatalytic reduction is still lacked. Herein, three kinds of functionalized CQDs, i.e. carboxylic CQDs (CCQDs), amino CQDs (NCQDs) and sulfonated CQDs (SCQDs), were homogeneously anchored on amino-rich g-C3N4 (U1W1-CN) to investigate their CO2 reduction behaviors under simulated solar-light illumination. Structural analysis demonstrated that potential amide covalent bonds formed between U1W1-CN and CCQDs, and noncovalent conjugations might exist between U1W1-CN and SCQDs, while strong electrostatic attraction between U1W1-CN and NCQDs. Performance tests showed CQDs decoration greatly enhanced the CO2 reduction activity, with 7%CCQDs/U1W1-CN exhibiting the optimal CO and CH4 productions of 40.94 μmol g−1 and 2.2 μmol g−1 under 4 h light irradiation, markedly higher than those of 7%SCQDs/U1W1-CN and 7%NCQDs/U1W1-CN. After comprehensive analysis, it was found that CCQDs decoration endowed U1W1-CN with better CO2 adsorption and activation. And due to the potential amide covalent bonds formed between CCQDs and U1W1-CN, 7%CCQDs/U1W1-CN delivered the largest electron density and most abundant COOH– intermediates, contributing much to its superior CO2 reduction activity over 7%NCQDs/U1W1-CN and 7%SCQDs/U1W1-CN. It is expected that the critical role of functional group modulation on CQDs in enhancing CO2 photocatalytic reduction revealed in this work can provide valuable insights into the rational design of more advanced photocatalysts for targeted reactions.

Rigidly Axial O Coordination-Induced Spin Polarization on Single Ni-N4-C Site by MXene Coupling for Boosting Electrochemical CO2 Reduction to CO.

Regulating the spin states in transition-metal (TM)-based single-atom catalysts (SACs), such as the TM-Nx-C configurations, is crucial for improving the catalytic activity. However, the role of spin in single Ni atoms facilitating the electrochemical CO2 reduction reaction (CO2RR) has been largely overlooked. Using first-principles simulations, we investigated the electrocatalytic performance of Ni-N4-C SACs vertically stacked on the O-terminated MXene nanosheets for the CO2RR. The terminated O atoms on MXene axially interact with the Ni atom due to significant charge transfer between them. Unlike the pure Ni-N4 site, which lacks spin polarization, the newly formed Ni-N4O configuration breaks the spin degeneracy of Ni d orbitals, dramatically lifting the energy level of spin-down d orbitals relative to that of spin-up d orbitals. As a result, the d electrons of Ni in the two spin channels are rearranged, leading to large net spin moments of 1.4 μB. Compared to the Ni-N4 site, the partially filled minority-spin dz2 orbitals of Ni on Ni-N4O weaken the occupied d-π* orbitals between Ni and *COOH, significantly stabilizing the key intermediate. The detailed reaction mechanisms and energetics show that four MXenes, namely, Hf3C2, Zr3C2, Hf2C, and Zr2C, can induce a large spin on the Ni site, thereby improving catalytic activity for CO2 reduction to CO, with a lower onset potential of about -0.75 V vs SHE compared to pure Ni SACs (-1.17 V) according to the potential-constant model with an explicit solvent environment.