Selective CO2 Reduction Research Articles

Structurally Asymmetric Ni−O−Mn Node in Metal–Organic Layers on Carbon Nitride Support for CO2 Photoreduction

AbstractThe Jahn–Teller (J–T) effect‐induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J–T distortion control over catalytic sites to enhance CO2 adsorption/activation and target‐product desorption remains a formidable challenge. In this work, we successfully induced J–T lattice distortion in neighboring Ni sites by exchanging high‐spin Mn2+ into Ni−O−Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni−O−Mn nodes induced structural contraction (shortened Ni−O bonds) in the adjacent Ni−O lattice. The magnetic hysteresis loop (M−H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni−O−Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d‐p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice‐mismatched Ni−O−Mn nodes exhibited an 8.79‐fold enhancement in CO production rate compared to the Ni−O−Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Regulating metal cation Cu vacancies on ZnIn2S4/Cu1.81S to achieve high selectivity for the photocatalytic reduction of CO2 to CH4

Photocatalytic reduction of CO2 is an effective pathway to achieve carbon neutrality. Herein, ZnIn2S4/Cu2-xS catalysts with S-type heterojunction was synthesized via hydrothermal method. By varying the ratio of the co-catalyst ZnIn2S4, the effects of the co-catalyst and Cu vacancies on the photocatalytic activity for CO2 and the selectivity for CH4 were investigated. The ZnIn2S4/Cu1.81S heterojunction catalyst with Cu vacancies exhibited optimal CH4 yield of 23.4 μmol·g-1·h-1 with selectivity of 98.11%. The cation Cu vacancies induce electron delocalization, modulating the electronic density of surrounding atoms to promote electron transfer efficiency, thereby accelerating the protonation of CO2 and improving both the yield and selectivity of CH4. This study integrates heterojunctions and defect engineering, providing a novel approach for the design of photocatalysts for CO2 reduction.

Recent Advances in Covalent Organic Framework (COF) for Selective Photocatalytic Reduction of CO2

Recent Advances in Covalent Organic Framework (COF) for Selective Photocatalytic Reduction of CO2

Two-dimensional QDs-Co-CuS1-x/Ti3C2/TiO2 heterojunction with synergistic unsaturated bimetal sites and sulfur vacancies for highly selective photocatalytic CO2 reduction

The primary factors that determine the efficiency and selectivity of multi-electron photoreduction of CO2 include the chemical properties of the active sites, as well as the kinetics of charge separation and transfer. Herein, a novel two-dimensional QDs-Co-CuS1-x/Ti3C2/TiO2 heterojunction is developed, with Co-CuS1-x quantum dots serving as cocatalysts and Ti3C2 MXene as an effective electron transfer channel. The anchoring effect of Ti3C2 facilitates the formation of robust TiS bonds with Co-CuS1-x, thereby promoting efficient separation and transfer of photoelectrons to the Co-Cu bimetallic active sites. This process enhances the local electron density at these sites and accelerates the kinetics of electron transfer to absorbed CO2. The recyclability of the Co-Cu sites is also significantly enhanced by continuous photoelectron injection. Importantly, DFT calculations indicate that the synergistic dual sites involving highly exposed Co-Cu and S vacancies promote rate-determining step from COO* to COOH*, which may account for the highly selective photoreduction of CO2-to-CO. Benefitting from the synergic effects of the active sites and efficient separation of carriers, the optimized Co-CuS1-x/Ti3C2/TiO2 exhibits a satisfactory CO photoreduction rate of 30.8 µmol∙g−1∙h−1, with an excellent selectivity of 87.9 % and apparent quantum yield of 0.61 % in the absence of any sacrificial reagents, which is 6.5 times higher than Co-CuS1-x, 54.0 times than Ti3C2Tx/TiO2.

Manipulating C-C coupling pathway in electrochemical CO2 reduction for selective ethylene and ethanol production over single-atom alloy catalyst.

Manipulation C-C coupling pathway is of great importance for selective CO2 electroreduction but remain challenging. Herein, two model Cu-based catalysts, by modifying Cu nanowires with Ag nanoparticles (AgCu NW) and Ag single atoms (Ag1Cu NW), respectively, are rationally designed for exploring the C-C coupling mechanisms in electrochemical CO2 reduction reaction (CO2RR). Compared to AgCu NW, the Ag1Cu NW exhibits a more than 10-fold increase of C2 selectivity in CO2 reduction to ethanol, with ethanol-to-ethylene ratio increased from 0.41 over AgCu NW to 4.26 over Ag1Cu NW. Via a variety of operando/in-situ techniques and theoretical calculation, the enhanced ethanol selectivity over Ag1Cu NW is attributed to the promoted H2O dissociation over the atomically dispersed Ag sites, which effectively accelerated *CO hydrogenation to form *CHO intermediate and facilitated asymmetric *CO-*CHO coupling over paired Cu atoms adjacent to single Ag atoms. Results of this work provide deep insight into the C-C coupling pathways towards target C2+ product and shed light on the rational design of efficient CO2RR catalysts with paired active sites.

Controlling Hydrogen Evolution and CO2 Reduction at Transition Metal Hydrides.

ConspectusFuel-forming reactions such as the hydrogen evolution reaction (HER) and CO2 reduction (CO2R) are vital to transitioning to a carbon-neutral economy. The equivalent oxidation reactions are also important for efficient utilization in fuel cells. Metal hydride intermediates are common in these catalytic and electrocatalytic processes. Guiding metal hydride reactivity is important for achieving selective, kinetically fast, and low overpotential redox reactions. Our work has focused on understanding kinetic and thermodynamic aspects for controlling these reactive hydride species in an effort to design more selective electrocatalysts that operate at low overpotentials. Key to our research approach is understanding the free energy changes and rate of discrete steps of catalysis through the synthesis of proposed intermediates to independently investigate catalytic steps. Hydricity, the free energy of hydride dissociation, and how these values change with metal and ligand environment have informed catalyst design in the past few decades. We describe here how we have advanced upon these earlier studies.In our early studies we sought to understand solvent-dependent changes in hydricity for transition metal hydrides and how they impact the free energy for reduction of CO2 to formate (HCO2-). Additionally, we described how hydricity values can be applied to optimize HER and CO2R catalysis. This framework provides general guidelines for achieving selective CO2 reduction to formate without concomitant generation of H2. Kinetic information on steps in the proposed catalytic cycle of HER and CO2R catalysts were evaluated to identify potential rate-determining steps. As a second approach to achieve selective reduction for CO2, we explored two catalyst design strategies to kinetically inhibit HER using electrostatic (charged) and steric interactions. Hydricity values and other considerations for minimizing the free energy of proposed catalytic steps were also used to design an electrocatalyst for the interconversion between CO2 and HCO2- at low overpotentials. Further, we discuss our efforts to translate the CO2 hydrogenation activity of homogeneous catalysts to electrocatalysis.All of these catalytic systems operate with classical metal hydrides, where the electrons and proton are colocated on the metal center. However, classical metal hydrides all require very reducing potentials to generate sufficiently strong hydride donors for CO2 reduction. An analysis of metal hydride hydricity and reduction potentials shows that the strong correlation between reduction potential and hydricity is a general trend because the former is also highly correlated to pKa. However, formate dehydrogenase (FDH) generates a competent hydride donor at more mild potentials through bidirectional hydride transfer, where the proton and electrons of the hydride are not colocated. This bioinspired approach points to a promising new strategy for generating strong hydride donors at milder potentials and will surely open new avenues for using hydricity as a guide for addressing new and existing problems in catalysis.

High-Entropy Metal Sulfide Promises High-Performance Carbon Dioxide Reduction.

The efficient conversion of carbon dioxide (CO2) requires the development of stable catalysts with high selectivity and reactivity within a wide potential range. Here, the high-entropy metal sulfide CuAgZnSnS4 is designed for CO2 reduction with excellent performance (FEcarbonproducts ≥ 90%) in whole test potential windows (600 mV) based on the synergistic effect of the high-entropy metal sulfide. In particular, CuAgZnSnS4 exhibits better single-product selectivity with the highest FEHCOOH/FECO value (29.03) at -1.28 versus reversible hydrogen electrode (RHE). In combination with in situ measurements and theoretical calculations, it is further revealed that the synergistic effect of CuAgZnSnS4 realizes the controllable regulation of the surface electronic structure at Sn active sites, strengthening orbital interactions between *OCHO and Sn active sites. As a result, the effective adsorption and activation of *OCHO instead of *H are obtained, improving the single-product selectivity of electrocatalytic CO2 reduction and inhibiting the competitive hydrogen evolution reaction significantly. Our findings may complete the understanding of the synergistic effect for high-entropy materials in catalysis and offer new insight into the design of efficient electrocatalysts with high catalytic activity.

Highly Selective Electroreduction of Carbon Dioxide Using Defect-Driven Catalysis.

The production of methanol from the electrochemical reduction of CO2 is a promising method of mitigating climate change while simultaneously producing a useful liquid fuel. In this study, we design self-assembled monolayers (SAMs) of thiols on metal and metal oxide electrodes that operate via cooperative catalysis between the thiolated surface sites and exposed electrode defect sites. This defect-driven mechanism enables the fabrication of SAM-modified ZnO electrodes that yield methanol with an extraordinarily high Faradaic efficiency of up to 92%. To understand the origin of this high selectivity, we study the effect of the chain length of the alkanethiols, different tail functional groups, and applied voltages on catalyst performance. These results combined with density functional theory calculations give a detailed atomic-level understanding of catalyst operation. Furthermore, the SAM linkage tolerates CO2 reduction conditions, and the catalyst's excellent selectivity for methanol remains high after 10 h of continuous conversion. Taken together, these findings with SAM-based electrodes convey a new and facile design strategy for the creation of highly selective CO2 reduction electrocatalysts.

Single-Atom-Layer Metallization of Plasmonic Semiconductor Surface for Selectively Enhancing IR-Driven Photocatalytic Reduction of CO2 into CH4.

Efficient harvesting and utilization of abundant infrared (IR) photons from sunlight is crucial for the industrial application of photocatalytic CO2 reduction. Plasmonic semiconductors have significant potential in absorbing low-energy IR photons to generate energetic hot electrons. However, modulating these hot electrons to selectively enhance the activity of CO2 reduction into CH4 remains a challenge. Herein, the study proposes a single-atom-layer (SAL) metallization strategy to enhance the generation of IR-driven hot electrons and facilitate their transfer from plasmonic semiconductors to CO2 for producing CH4. This strategy is demonstrated using a paradigmatic W18O49@W-Sn nanowire array (NWA), where Sn2+ ions are grafted onto exposed O atoms on the surface of plasmonic W18O49 to form a surface W-Sn SAL. The incorporation of Sn single atoms enhances plasmonic absorption in IR light for W18O49 NWA. The W-Sn SAL not only promotes CO2 adsorption and reduces its reaction activation energy barrier but also shifts the endoergic CO-protonation process toward an exoergic reaction pathway. Thus, the W18O49@W-Sn NWA exhibits >98% selectivity for IR-driven CO2 reduction to CH4 with an activity over 9.0 times higher than that of bare W18O49 NWA. This SAL metallization strategy can also be applied to other plasmonic semiconductors for selectively enhancing CO2-to-CH4 reduction reactions.

Manipulating adsorbed hydrogen on lanthanum-modified CuOx: Industrial-current-density CO2 electroreduction to C2+ products or CH4

The selective electrochemical CO2 reduction reaction (CO2RR) yields valuable C2+ and C1 products, yet the influence of adsorbed hydrogen (*H) on product distribution remains inadequately understood. This study explores this effect by developing bimetallic copper-based electrocatalysts with varied lanthanum (La) doping ratios. The oxide-derived (OD)-La0.10-CuOx catalyst exhibits a Faradaic efficiency (FE) over 80% for C2+ products at 300 mA cm−2, whereas OD-La0.40-CuOx achieves a 61.4% FECH4 at 400 mA cm−2. Kinetic isotope experiments reveal distinct dependencies of the rate-determining steps on *H transfer for CO2RR in OD-La0.10-CuOx and OD-La0.40-CuOx. In situ ATR-SEIRAS and DFT calculations demonstrate that the moderate H2O dissociation capability of OD-La0.10-CuOx lowers the energy barrier for *CHO → *OCCHO conversion, thus increasing the FEC2+. Conversely, OD-La0.40-CuOx, with its strong H2O dissociation capability, favors *CHO → *CH2O, thereby promoting CO2RR-to-CH4. These findings advance the understanding of the role of *H in CO2 electroreduction at industrial current densities and present avenues for tailored CO2RR products via doping engineering.

Construction of a sunflower-like S-scheme WO3/ZnIn2S4 heterojunction with spatial charge transfer for enhanced photocatalytic CO2 reduction

The construction of step-scheme (S-scheme) heterojunction has become an effective strategy for enhancing photocatalytic CO2 reduction. In this study, a sunflower-like S-scheme WO3/ZnIn2S4 heterostructure is fabricated through the in-situ growth of ZnIn2S4 nanosheets on WO3 hollow sphere, aimed at improving selective CO2 reduction. The constructed embedding configuration, featuring a WO3 hollow sphere core and an outer layer of ZnIn2S4 nanosheet, increases the contact interface and establishes a significant built-in electric field, thereby promoting the migration and separation of photogenerated carriers. The confined internal cavity of the three-dimensional (3D) sunflower-like architecture aids in limiting the free diffusion of CO2, and enriching CO2 molecules at the surface of the photocatalyst, consequently enhancing reaction kinetics.Moreover, S vacancies on ZnIn2S4 nanosheets promote the chemisorption and activation of CO2. As a result, the optimized evolution rates for CH4 and CO of 58.7μmol g–1h−1 and 51.3μmol g–1h−1, respectively, are achieved for WO3/ZnIn2S4 heterojunction. The corresponding electron selectivity for CH4 reaches 82.1 %, which is 13 and 1.5 times higher than those of bare WO3 and ZnIn2S4, respectively. This provides valuable insights into the design of muti-functionalized S-scheme heterojunction photocatalysts.

Specific Adsorption of Alkaline Cations Enhances CO-CO Coupling in CO2 Electroreduction.

Electrolyte alkaline cations can significantly modulate the reaction selectivity of electrochemical CO2 reduction (eCO2R), enhancing the yield of the valuable multicarbon (C2+) chemical feedstocks. However, the mechanism underlying this cation effect on the C-C coupling remains unclear. Herein, by performing constant-potential AIMD simulations, we studied the dynamic behavior of interfacial K+ ions over Cu surfaces during C-C coupling and the origin of the cation effect. We showed that the specific adsorption of K+ readily occurs at the surface sites adjacent to the *CO intermediates on the Cu surfaces. Furthermore, this specific adsorption of K+ during *CO-*CO coupling is more important than quasi-specific adsorption for enhancing coupling kinetics, reducing the coupling barriers by approximately 0.20 eV. Electronic structure analysis revealed that charge redistribution occurs between the specifically adsorbed K+, *CO, and Cu sites, and this can account for the reduced barriers. In addition, we identified excellent *CO-*CO coupling selectivity on Cu(100) with K+ ions. Experimental results show that suppressing surface K+-specific adsorption using the surfactant cetyltrimethylammonium bromide (CTAB) significantly decreases the Faradaic efficiency for C2 products from 41.1% to 4.3%, consistent with our computational findings. This study provides crucial insights for improving the selectivity toward C2+ products by rationally tuning interfacial cation adsorption during eCO2R. Specifically, C-C coupling can be enhanced by promoting K+-specific adsorption, for example, by confining K+ within a coated layer or using pulsed negative potentials.

Controlling the Phase Composition of Pre-Catalysts to Obtain Abundant Cu(111)/Cu(200) Grain Boundaries for Enhancing Electrocatalytic CO2 Reduction Selectivity to Ethylene.

The preparation of ethylene (C2H4) by electrochemical CO2 reduction (ECO2R) has dramatically progressed in recent years. However, the slow kinetics of carbon-carbon (C-C) coupling remains a significant challenge. A generalized facet reconstruction strategy is reported to prepare a 3-phase mixed pre-catalyst (Cu3N-300) of Cu3N, Cu2O, and CuO by controlling the calcination temperature and to obtain the derived Cu catalyst (A-Cu3N-300-0.5) enriched with Cu(111)/Cu(200) grain boundaries (GBs) by subsequent constant potential reduction. Its Faraday efficiency (FE) toward C2H4 at a low reaction potential of -1.07V (vs reversible hydrogen electrode (RHE)) is 46.03%, which is much higher than the other 3 derived Cu catalysts containing single Cu(111) facets (24.89% and 24.52%) and Cu(111)/Cu(111) GBs (28.66%). Combining in situ experimental and theoretical computational studies, abundant Cu(111)/Cu(200) GBs is found to enhance CO2 activation and significantly promote the formation and adsorption of *CO intermediates, thereby lowering the activation energy barrier of C-C coupling and increasing the FE of C2H4.

Synergistic effect between amino functional group and graphene oxide in selective photocatalytic CO2 reduction to formic acid

Carbon dioxide (CO2) reduction to useful possible chemicals is of great significance to energy supply, while formic acid is one of the most desirable product among the many other chemicals. In this study, a novel reduced graphene oxide (rGO) coupled doped TiO2 with NH2-MIL-125(Ti)(TiM) composite photocatalysts TiO2@rGO@TiM was designed by using a solvent-thermal method to facilitate the photocatalytic CO2 reduction to formic acid under the visible light. Benefiting from the special structure of TiO2@rGO@TiM, up to a rate of 113 µmol•g−1•h−1 of formic acid was produced in a photochemical process, which is four times greater than that of pure TiO2 and TiM without any sacrificial agent. The results of structure and photoelectrochemical characterization demonstrated that the enhanced production of formic acid was attributable to the synergistic effect generated by the incorporation of the amino functional group and reduced graphene oxide, resulting in the effective photo-induced carrier spatial segregation and transfer and improving the catalytic activity.

Second sphere control of CO2 reduction selectivity by iron porphyrins: The role of spin state

Iron porphyrins are reported to reduce CO2 selectively to CO. Hydrogen bonding interactions are reported to facilitate this 2e−/2H+ reduction process. A series of iron porphyrins are reported here where hydrogen bonding distal super structure is introduced systematically. The results show that the selectivity for 2e−/2H+ CO2 reduction changes dramatically from CO to HCOOH as hydrogen bonding interactions are introduced. The resonance Raman data of the Fe(II)-COOH intermediate, trapped at −80oC, show that the spin state of this species changes from low spin to high spin as hydrogen bonding is introduced. The spin state of the Fe(II)-COOH intermediate seems to determine the selectivity of 2e−/2H+ CO2 reduction in iron porphyrins.

Water-Induced Switching in Selectivity and Steric Control of Activity in Photochemical CO2 Reduction Catalyzed by RhCp*(bpy) Derivatives.

Photocatalytic reduction of CO2 to formic acid (HCOOH) was investigated in either organic or aqueous/organic media by employing three water-soluble [RhIIICp*(LH2)Cl]+ (LH2 = n,n'-dihydroxy-2,2'-bipyridine; n = 4, 5, or 6) in the presence of [Ru(bpy)3]2+, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) and triethanolamine (TEOA). Through studying the electron-donating effects of two hydroxyl groups introduced into the bipyridyl ligand, we found that the substituent positions greatly affect both the catalytic efficiency and selectivity in CO2 reduction. More importantly, the HCOOH selectivity shows a dramatic increase from 14 to 83% upon switching the solvent media from pure organic to an aqueous/organic mixture, where the H2 selectivity shows a reverse phenomenon. The enhanced HCOOH selectivity and the drastic decrease in the H2 yield are well rationalized by the fact that the catalytic CO2 hydrogenation is not only driven photochemically via the attack of RhIII(H)Cp*(LH2-·) on CO2 but also partly bypassed by a dark H2 addition reaction yielding [RhIII(H)Cp*(L)]- from [RhIIICp*(L)Cl]+, which was also separately investigated under dark conditions. A combination of experimental and theoretical approaches was made to clarify the pKa values of catalyst intermediates together with the abundant species responsible for the major catalytic processes. Our DFT studies unveil that the exceptionally large structural strain given by the steric contacts between the 6,6'-dihydroxyl groups and the Cp* moiety plays a significant role in bringing about an outstanding catalytic performance of the 6,6'-substituted derivative. The intrinsic reaction coordinate calculations were carried out to clarify the mechanism of hydride transfer steps leading to generating formate together with the heterolytic H2 cleavage steps leading to afford the key hydridorhodium intermediates. This study represents the first report on the water-induced high selectivity in CO2-to-HCOOH conversion, shedding new light on the strategy to control the efficiency and selectivity in the catalysis of CO2 reduction.

Molecular catalyst coordinatively bonded to organic semiconductors for selective light-driven CO2 reduction in water

The selective photoreduction of CO2 in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO2 photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber. This generates a molecular hybrid material that efficiently and selectively achieves the photoreduction of CO2 to CO in KHCO3 aqueous buffer, giving high yields in the range of 22 mmol g−1 (458 μmol g−1 h−1) and turnover numbers above 550 in 48 h, with no deactivation and no detectable H2. The electron transfer mechanism for the activation of the catalyst is proposed based on the combined results from time-resolved fluorescence spectroscopy, in situ spectroscopies and quantum chemical calculations.

Physicochemical Analysis of Cu(II)-Driven Electrochemical CO2 Reduction and its Competition with Proton Reduction.

The reduction of CO2 has become a key role in reducing greenhouse gas emissions in efforts to search for long-term responses to climate change. We report a a couple of CO2-reducing molecular catalysts based on earth-abundant copper complexes. These are [Cu(DPA)(PyNAP)] (1) and [Cu(DPA)(PyQl)] (2) (where, DPA = pyridine-2,6-dicarboxylic acid, PyNAP = 2-(pyridin-2-yl)-1,8-naphthyridine, and PyQl = 2-(pyridin-2-yl)quinoline). The copper metal-catalysed 2-electron reduction of CO2 to CO in the presence of 2-protons is challenging. These catalysts exhibit the production of CO gas in DMF/water mixtures, achieving an impressive faradaic efficiency of 84% and 72% for complex 1 and 2 at -1.7 V vs. SCE, respectively, for selective CO2 reduction. The production of H2 due to 2H+ + 2e- was also observed as a byproduct through the competitive proton reduction reaction. This was cross-verified by online gas and mass analysis.Our investigations confirmed the stability of the electrocatalysts under the electrocatalytic conditions. The mechanistic pathways were proposed to work with the EECC and ECEC (E: electrochemical and C: chemical) mechanisms. A CO2 insertion into an in-situ generated hydride from the Cu-center generates CO through the favourable path.

Unveiling the Structural Effects in Hybrid Copper Phosphonate Frameworks for Selective Electrocatalytic CO2 Reduction Reaction.

Electrochemical CO2 reduction holds tremendous promise for transforming carbon dioxide into several value-added energy feedstocks and utilizing renewable energy sources. Herein, we have developed two novel copper-based organophosphonates for selective electrocatalytic conversion of CO2 to CH3OH conversion. The two-dimensional layer structure of Cu3[(Hhedp)2(C4H4N2)].2H2O (I) and the three-dimensional Cu3[(H3hedp)2(C4H4N2)4(SO4)].2H2O (II) have been isolated as single crystals via a hydrothermal strategy. Compound I consists of Cu2+ oxidation states exclusively, while compound II has Cu1+ oxidation states in a network wherein a Cu2+-phosphonate template is embedded inside the framework. Depending on mixed valent oxidation states, compound II exhibits high selectivity compared to compound I for the electrocatalytic reduction of CO2 to CH3OH (C1) as the primary product and CH3COOH (C2) as the secondary product. Notably, product selectivity is enhanced as the Faradaic efficiency (FE) of the competing hydrogen evolution reaction (HER) is significantly reduced in compound II relative to that of I, particularly at higher applied reduction potentials. The optimal ratio of Cu1+ active sites in compound II plays a pivotal role in enhancing methanol selectivity, stabilizing critical intermediates, and maintaining ideal reduction potentials as a noble-metal free electrocatalyst. Moreover, the optical band gap and the Mott-Schottky measurements further suggest the title Cu-phosphonate materials could be promising and effective photocatalysts.

Revisiting the origin of enhanced C2+ selectivity on oxide-derived copper toward CO2 electroreduction

Oxide-derived copper (OD-Cu) exhibits remarkable efficiency toward selective electrochemical reduction of CO2 to high-energy-density multicarbon (C2+) products. The big challenge, however, lies in accurately discerning the actual chemical state of copper in OD-Cu that enhances C2+ selectivity, which are largely dictated by the intricating dynamic structural evolution of copper under operating conditions. Herein, we report the construction of a core-shell structured Cu wire model catalyst with a pristine metallic Cu core and an OD-Cu shell using a flame-quenching approach. The cross-section of this model catalyst, merging the surfaces of both pristine Cu and OD-Cu, serves as an ideal platform for probing the structural evolution and discerning the distinct roles of metallic and oxidative Cu in CO2 electroreduction. Through a combination of in situ and ex situ techniques, we unambiguously identify the presence of Cu+ and Cu0 within OD-Cu under electrochemical operating conditions. Furthermore, the cross-examination of theoretical and experimental infrared spectroscopic data unravels that the enhanced C2+ selectivity over the OD-Cu shell primarily stemmed from the tandem coupling of Cu0 with Cu+, which improves the kinetics of C-C coupling. These findings not only offer refreshing perspective on the chemical state of OD-Cu but also provide new guidelines for designing and constructing new high-performance electrocatalysts for CO2 reduction.