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Electrocatalysis, as a typical heterogeneous catalysis, generally occurs in the di- or tri-phase interfaces. Wettability is an important property for describing the balance of a gas-liquid-solid system. Therefore, the wettability of reaction interface, especially hydrophilicity/hydrophobicity, plays an important role in the adsorption/desorption process of gas bubbles on the surface of the solid electrode. Herein, we present a comprehensive review of the wettability control of the electrode materials applied in electrocatalysis reactions, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR). Firstly, the basic theories of wettability as well as the impact on electrocatalysis were introduced in this review. Secondly, the overview of modifying methods of the wettability from electrocatalyst microstructure (structural modification, surface coating, introducing hydrophilic groups) and system design (electrode, device) were suggested. At last, the deficiencies and problems in the application of wettability control are discussed, and deeper and broader application prospects are proposed.

Carbon dioxide reduction (CRR) is an attractive strategy for alleviating global warming and producing valuable fuels. In this work, we study the catalytic conversion of CO2 to C1-C3 products on boron nanosheet in the presence of compressive strain by using density functional theory. Thermodynamic and microkinetic models are applied to demonstrate the favorable products, critical steps, and hydrogenation mechanisms. As demonstrated, the strain can turn metallic two-dimensional boron nanosheet to semiconductor, not only making boron sheets possess photo(electro)catalytic activity, but also improving energy efficiency and selectivity performance against hydrogen evolution reaction. By introducing the aqueous electrolytes, the hydrated alkali cations not only effect on the CO2 concentration, but also produce a bigger surface charge density and stronger interfacial electric filed. Especially, the selectivity of C2+ products is enhanced with the increase of alkali cations size by decreasing the kinetic barrier for CO dimerization and stabilizing the intermediates. The results highlight the significance of metal-free catalysts for CRR by the photoelectrochemical method and provide novel avenues for the development of new solar-energy utilization catalysts.

Electrochemical carbon dioxide reduction (CO2RR) plays an important role in solving the problem of high concentration of CO2 in the atmosphere and realizing carbon cycle. Core-shell structure has many unique features including tandem catalysis, lattice strain effect, defect engineering, which exhibit great potential in electrocatalysis. In this review, we focus on the advanced core-shell metal-based catalysts (CMCs) for electrochemical CO2RR. The recent progress of CMCs in electrocatalytic CO2RR is described as the following aspects: (1) The mechanism of electrochemical CO2RR and evaluation parameters of electrocatalyst performance, (2) preparation methods of core-shell metal catalysts and core-shell structural advantages and (3) advanced CMCs towards electrochemical CO2RR. Finally, we make a brief conclusion and propose the opportunities and challenges in the field of electrochemical CO2RR.

In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance. This aspect can be investigated by employing a model that depicts the local environment for the reduction reactions. Simultaneously, electrochemical impedance spectroscopy, despite being a versatile technique, has rarely been adopted for studying the mass transport features during the carbon dioxide (CO2) electroreduction. In this work, this aspect is deeply analyzed by correlating the results of impedance spectroscopy characterization with those obtained by a bubble-induced mass transport modeling under controlled diffusion conditions on a gold rotating disk electrode. The effects of potential and rotation rate on the local environment are also clarified. In particular, it has been found that CO2 depletion occurs at high kinetics when the rotation is absent, giving rise to an increment of the competing hydrogen evolution reaction. This feature reflects in an enlargement of the diffusion resistance, which overcomes the charge transport one.

Copper (Cu) provides a cost-effective means of producing value-added fuels through the electrochemical reduction of carbon dioxide (CO2RR). However, we observed the production of hydrocarbons via CO2RR on commercial Cu films is less efficient because of the surface impurities, i.e., Fe. Carbon monoxide (CO), a reaction intermediate of CO2RR to hydrocarbons, binds strongly to the Fe sites and interrupts the production of hydrocarbons, resulting in an active hydrogen evolution reaction (HER). Herein, we report a method of blocking the effect of Fe impurities on the Cu surface through the preferential growth of nano-sized metal-organic frameworks (MOFs) on Fe site. When zirconium (Zr)-based MOFs (UiO-66) forms a compensating layer on Cu film via the terephthalic acid (TPA)-Fe coordination bond, the UiO-66 coated Cu film (UiO-66@Cu) presents significantly improved hydrocarbon Faradaic efficiency (FE) of 37.59% compared to 14.68% FE on commercial Cu film (99.9% purity) by suppressing HER. According to X-ray photoelectron spectroscopy (XPS) analysis, the UiO-66 ligand binds to entire metallic Fe site on the Cu surface, while metallic Cu is retained. Thus, UiO-66@Cu provides active sites of Cu for CO2RR and leads to highly efficient and selective production of hydrocarbons.

The formation of interfacial chemical bonding in heterostructures plays an important role in the transport of carriers. Herein, we firstly prepared ultrathin InVO4 nanosheet (Ns) with a thickness of 1.5 nm. Diethylenetriamine-modified CdSe (CdSe-DETA) nanobelts are in-situ deposited on the surface of ultrathin InVO4 Ns to build a InVO4/CdSe-DETA step-scheme (S-scheme) heterojunction photocatalysts. The protonated DETA acts as an amine-bridge to promote the formation of a tight chemical bond at the interface of InVO4/CdSe-DETA, thereby promoting the transfer of carriers at the interface. For photocatalytic CO2 reduction, the rationally designed InVO4/CdSe-DETA S-scheme photocatalyst exhibits a remarkable CO generation rate of 27.9 µmol h−1 g−1 at 420 nm, which is 3.35 and 3.39 times higher than that of CdSe-DETA and InVO4 Ns, respectively. The new method by using interfacial chemical bonding to facilitate interfacial charge transportation provide a promising strategy for improve photocatalysis.

The electrosynthesis of valuable chemicals via carbon dioxide reduction reaction (CO2RR) has provided a promising way to address global energy and sustainability problems. However, the selectivity and activity of deep-reduction products (DRPs) still remain as big challenges. Here, a copper–carbon-based catalyst with a hydrophobic core–shell architecture has been constructed and was found to exhibit excellent DRPs of methane generation with a faradaic efficiency of 81 ± 3% in a neutral medium and a maximum partial current density of −434 mA cm−2 in a flow cell configuration, which is among the best of CO2-to-CH4 electrocatalysts. Density functional theory calculations suggest that the hydrophobic structure decreasing the water coverage on the catalyst surface can promote the protonation of the *CO intermediate and block CO production, further favoring the generation of methane. These results provide a new insight into the electrosynthesis of DRPs via constructing a hydrophobic core–shell architecture for tuning the surface water coverage.

Herein, we report the results from our study towards understanding the role of electrocatalyst surfaces and solvents (aqueous versus wet organic media) in C–C bond formation on microstructured spheres, polygons, aggregates and dendrites of copper, which is a crucial aspect for the selective and sustainable conversion of CO2 into high energy density hydrocarbons like ethylene. Our results establish that apart from morphology, the crystal orientations and characteristic electrode/electrolyte interfacial physico-chemical aspects significantly affect the electrochemical carbon dioxide reduction (ECR) reaction activity and selectivity of copper electrocatalysts. Moreover, we report that an appropriate combination of catalyst properties and solvent/electrode interface ensures selective electroreduction of CO2 into C1 and C2 hydrocarbons, especially ethylene, over dendritic copper electrocatalysts. We demonstrate that for a given solvent system, the morphology of the electrocatalyst is the sole determinant of its catalytic activity, with elaborate dendritic shape enhancing the ECR reaction irrespective of the solvent used. A detailed account of the electrocatalytic performance, product selectivity, and faradaic efficiency of Cu-electrodeposits for ECR in aqueous medium and wet-organic (DMSO) electrolyte is presented. In aqueous 0.2 M KHCO3 solution, the catalyst exhibits a faradaic efficiency of 43% for ethylene production at −1.0 V vs. RHE and a selectivity of 74% among all the hydrocarbon products. Importantly, the Cu-based electrocatalysts fabricated for the present study inhibit the parasitic hydrogen evolution reaction and production of parallel products, viz. CO, CH4, and C2H6, during the ECR. Our results further establish that C–C coupling for the formation of ethylene is affected by the nano-morphology of the electrocatalyst and the composition of the electrolyte system employed for the electroreduction.

Electrocatalytic carbon dioxide reduction (CO2R) presents a promising route to establish zero-emission carbon cycle and store intermittent renewable energy into chemical fuels for steady energy supply. Methanol is an ideal energy carrier as alternative fuels and one of the most important commodity chemicals. Nevertheless, methanol is currently mainly produced from fossil-based syngas, the production of which yields tremendous carbon emission globally. Direct CO2R towards methanol poses great potential to shift the paradigm of methanol production. In this perspective, we focus our discussions on producing methanol from electrochemical CO2R, using metallomacrocyclic molecules as the model catalysts. We discuss the motivation of having methanol as the sole CO2R product, the documented application of metallomacrocyclic catalysts for CO2R, and recent advance in catalyzing CO2 to methanol with cobalt phthalocyanine-based catalysts. We attempt to understand the key factors in determining the activity, selectivity, and stability of electrocatalytic CO2-to-methanol conversion, and to draw mechanistic insights from existing observations. Finally, we identify the challenges hindering methanol electrosynthesis directly from CO2 and some intriguing directions worthy of further investigation and exploration.

Summary The renewable-energy-driven conversion of CO2 is an important means of generating carbon-based fuels and chemicals to power a sustainable society. While most CO2 reduction (CO2R) is carried out in alkaline electrolyte, working in such conditions often leads to spontaneous carbonate formation and, consequently, a low energy balance and CO2 utilization rate. Alternatively, operating in acid alleviates these issues, but achieving selective CO2R in the presence of high proton concentrations has proven to be a challenge over the years. Recently, a host of works have emerged that have demonstrated both a proof of concept and initial design principles for CO2R in acid. As such, this perspective will cover the key initial findings that steer catalysis towards CO2R. After an overview of successful systems, we turn to the future in examining what key questions remain and steps can be taken in this emerging area to bring CO2R in acid toward practical feasibility.

Metal-N4 (M-N4) macrocyclic complexes are interesting electrocatalysts due to their well-defined structures and rich molecular tuning. Among them, metal phthalocyanines have been widely studied for the carbon dioxide reduction reaction (CO2RR) in heterogeneous systems and demonstrated good electrocatalytic performance. However, other complexes like metal corroles and metal porphyrins are much less explored, and often show inferior performances. In this study, three cobalt macrocyclic complexes, cobalt phthalocyanine, cobalt meso-tetraphenylporphyrin, and cobalt meso-triphenylcorrole (CoPc, CoTPP and CoTPC) are investigated in heterogeneous electrocatalysis of CO2RR. Although CoPc/carbon nanotube (CNT) hybrid exhibits high electrocatalytic activity, CNT hybridization does not work for CoTPC and CoTPP that hold weak interactions with CNTs. By the drop-dry method with a high molecular loading of 5.4 × 10–7 mol cm–2, CoTPC and CoTPP could deliver appreciable electrode activities. Poly(4-vinylpyridine) (PVP) introduction is further demonstrated as a facile method to afford enhanced activities for CoTPP at low molecular loadings through enhancing molecule-substrate interactions. The partial current density of carbon monoxide for CoTPP+CNT/PVP is around 8 times higher than the sample without PVP at –0.67 V versus reversible hydrogen electrode. This work provides solutions to enhance the electrode activities of molecular electrocatalysts with weak substrate interactions in heterogeneous systems.

With the rising global population, increasing energy demand and rapid climate change, great concerns have been raised for environment and energy security in future. Solar-driven CO2 reduction provides a promising way to deal with energy crisis and global warming, which has been widely concerned. Photoelectrocatalysis technology can effectively utilize solar energy and avoid to use high-temperature and high-voltage reduction environment by integrating the vantages of both photocatalysis and electrocatalysis, which exhibits a broad application prospect of CO2 reduction with a high efficiency and excellent selectivity. In this review, basic principles of CO2 reduction by photocatalysis, electrocatalysis and photoeletrocatalysis are briefly reviewed, also comparing the technical characteristics of the above technologies. Different photoelectrocatalytic systems for CO2 reduction are described and compared. The several key influencing factors of photoelectrocatalytic performance of CO2 reduction are discussed, including interaction between reaction molecules and catalysts, reaction conditions and influence of photoelectrode. Then, the advances on reaction mechanisms and strategies of performance enhancement by optimizing photoexcitation, charge separation efficiency and surface reaction were reviewed. Besides, the challenges and prospects of photoelectrocatalytic CO2 reduction will be also discussed.

The review summarizes the current knowledge about heterogeneous semiconductor photocatalysts that are active towards photocatalytic reduction of carbon dioxide and molecular nitrogen under visible and near-UV light. The main classes of these photocatalysts and characteristic features of their application in the target processes are considered. Primary attention is given to photocatalysts based on titanium dioxide, which have high activity and stability in the carbon dioxide reduction. For the first time, the photofixation of nitrogen under irradiation in the presence of various semiconductor materials is considered in detail.The bibliography includes 264 references.

Coordination engineering can enhance the activity and stability of the catalyst in heterogeneous catalysis. However, the axial coordination engineering between different groups on the carbon carrier and molecular catalysts in the electrocatalytic carbon dioxide reduction reaction (CO2RR) has been studied rarely. Through coordination engineering strategy, a series of amino (NH2), hydroxyl (OH), and carboxyl (COOH) groups functionalized carbon nanotubes (CNT) immobilized cobalt phthalocyanine (CoPc) catalysts are designed. Compared with no groups, OH groups and COOH groups, NH2 groups can effectively change the coordination environment of the central metal Co, thereby significantly increasing the turnover frequency (TOF) (31.4 s−1 at −0.6 V vs. RHE, CoPc/NH2-CNT > CoPc/OH-CNT > CoPc/COOH-CN > CoPc/CNT). In the flow cell, the CoPc/NH2-CNT catalyst has high carbon monoxide (CO) selectivity at high current density (∼ 100% at −225 mA·cm−2, ∼ 96% at −351 mA·cm−2). Importantly, the CoPc/NH2-CNT catalyst can operate stably for 100 h at 225 mA·cm−2. Theoretical calculations reveal that CoPc/NH2-CNT catalyst is beneficial to the formation of *COOH and desorption of *CO, thus promoting CO2RR. This work provides an excellent platform for understanding the effect of coordination engineering on electrocatalytic performance and promotes a way to explore efficient and stable catalysts in other applications.

ConspectusWhile developed in a number of directions, bioinspired catalysis has been explored only very recently for CO2 reduction, a challenging reaction of prime importance in the context of the energetic transition to be built up. This approach is particularly relevant because nature teaches us that CO2 reduction is possible, with low overpotentials, high rates, and large selectivity, and gives us unique clues to design and discover new interesting molecular catalysts. Indeed, on the basis of our relatively advanced understanding of the structures and mechanisms of the active sites of fascinating metalloenzymes such as formate dehydrogenases (FDHs) and CO dehydrogenases (CODHs), it is possible to design original, active, selective, and stable molecular catalysts using the bioinspired approach. These metalloenzymes use fascinating metal centers: in FDHs, a Mo(W) mononuclear ion is coordinated by four sulfur atoms provided by a specific organic ligand, molybdopterin (MPT), containing a pyranopterin heterocycle (composed of a pyran ring fused with a pterin unit) and two sulfhydryl groups for metal chelation; in CODHs, catalytic activity depends on either a unique nickel-iron-sulfur cluster or a dinuclear Mo-Cu complex in which the Mo ion is chelated by an MPT ligand. As a consequence, the novel class of catalysts, designed by bioinspiration, consists of mononuclear Mo, W, and Ni and as well as dinuclear Mo-Cu and Ni-Fe complexes in which the metal ions are coordinated by sulfur ligands, more specifically, dithiolene chelates mimicking the natural MPT cofactor. In general, their activity is evaluated in electrochemical systems (cyclic voltammetry and bulk electrolysis) or in photochemical systems (in the presence of a photosensitizer and a sacrificial electron donor) in solution. This research is multidisciplinary because it implies detailed biochemical, functional, and structural characterization of the inspiring enzymes together with synthetic organic and organometallic chemistry and molecular catalysis studies. The most important achievements in this direction, starting from the first report of a catalytically active biomimetic bis-dithiolene-Mo complex in 2015, are discussed in this Account, highlighting the challenging issues associated with synthesis of such sophisticated ligands and molecular catalysts as well as the complexity of reaction mechanisms. While the very first active biomimetic catalysts require further improvement, in terms of performance, they set the stage in which molecular chemistry and enzymology can synergistically cooperate for a better understanding of why nature has selected these sites and for developing highly active catalysts.

Electrocatalysis has become an attractive strategy for the artificial reduction of CO2 to high-value chemicals. However, the design and development of highly selective and stable non-noble metal electrocatalysts that convert CO2 to CO are still a challenge. As a new type of two-dimensional carbon material, graphdiyne(GDY), is rarely used to explore the application in carbon dioxide reduction reaction(CO2RR). Therefore, we tried to use GDY as a substrate to stabilize the copper-nickel alloy nanoparticles(NPs) to synthesize Cu/Ni@GDY. Cu/Ni@GDY requires an overpotential (−0.61 V) to 10 mA/cm2 for the formation of CO, and it shows better activity than Au and Ag, achieving a higher Faraday efficiency of about 95.2% and high stability of about 26 h at an overpotential (−0.70 V). The electronic interaction between GDY substrate and Cu/Ni alloy NPs and the large specific surface area of GDY is responsible for the high performance.

A bis(pyridyl)amine-bipyridine-iron(II) framework (Fe(BPAbipy)) of complexes 1-3 is reported to shed light on the multistep nature of CO2 reduction. Herein, photocatalytic conversion of CO2 to CO even at low CO2 concentration (1 %), together with detailed mechanistic study and DFT calculations, reveal that 1 first undergoes two sequential one-electron transfer affording an intermediate with electron density on both Fe and ligand for CO2 binding over proton. The following 2 H+ -assisted Fe-CO formation is rate-determining for selective CO2 -to-CO reduction. A pendant, proton-shuttling α-OH group (2) initiates PCET for predominant H2 evolution, while an α-OMe group (3) cancels the selectivity control for either CO or H2 . The near-unity selectivity of 1 and 2 enables self-sorting syngas production at flexible CO/H2 ratios. The unprecedented results from one kind of molecular catalyst skeleton encourage insight into the beauty of advanced multi-electron and multi-proton transfer processes for robust CO2 RR by photocatalysis.

In photocatalysis, the most efficient way to separate photogenerated electron-hole pairs has been extensively studied. However, the methods to increase the quantities of free electrons are neglected. Herein, we used a self-assembly method to fabricate MTCPP/TiO2 composite materials with a series of metalloporphyrins (MTCPPs, M = Fe, Co, Zn) as sensitizers to modify TiO2 nanosheets. First, abundant carboxyl and hydroxyl on porphyrin were adsorbed by metal ions. Then, the remaining carboxyl and hydroxyl on porphyrin were anchored on the surface of TiO2 nanosheets. Finally, MTCPP/TiO2 was obtained by a layer-by-layer self-assembly process. MTCPP broadens the light response of TiO2 from ultraviolet light to visible light and enhances the CO2 adsorption ability. Moreover, metal ions coordinating with porphyrin regulate the electron density of the porphyrin ring and provide a stronger π feedback bond, which promote charge separation. Consequently, by optimizing the type of metal ion, the yield of ZnTCPP/TiO2 composites reached 109.33 μmol/(g h) of CO and 9.94 μmol/(g h) of CH4, which was more than 50 times that of pure TiO2. This study proposes a possible visible-light-induced CO2 reduction mechanism of metal-ion-based photocatalysis, which provides great insights into optimizing the designation of efficient photocatalysis.

Current major electrocatalytic reactions, such as hydrogen evolution reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction, focus on single-target chemical production, which suffers from strong competitive reactions at the same electrodes and/or high energy barrier reactions at the counterpart electrodes. The co-electrolysis of more than one kind, typically two kinds, of chemical precursors in one electrolytic system is therefore a highly attractive strategy for both energy input reduction and concurrent production of double value-added chemicals. Exciting progress has been achieved in this area recently, and a timely review on this specific topic will be highly desired. In this review, the reported co-electrolysis systems are classified into four categories: (1) agent sacrificing at one electrode promoting electrochemical precursor conversion at the other; (2) parallel electrochemical precursor conversions, i.e., electrosyntheses, simultaneously at both sides; (3) electrochemical conversions of two precursors at both sides into one/the same product; (4) double/multiple electrochemical conversions at one side. The current challenges and future opportunities of co-electrolysis toward high value-added products are discussed at the end.

The electrocatalytic CO2 reduction reaction (CO2RR) decreases the amount of greenhouse gas in the atmosphere while enabling a closed carbon cycle. Herein, iron oleate was used as a precursor to produce oleic acid-coated triiron tetraoxide nanoparticles (Fe3O4@OA NPs) by pyrolysis, which was then assembled with reduced graphene oxide (rGO) and doped with dicyandiamide as a nitrogen source to obtain nitrogen-doped iron carbide nanoparticles assembled on rGO (N-Fe3C/rGO NPs). The catalyst prepared by nitrogen doping at 800 °C with an Fe3O4@OA NPs to rGO weight ratio of 20:1 showed good activity and stability for the CO2RR. At −0.3 to −0.4 V, the H2/CO ratio of the product from the catalyzed CO2RR was close to 2; thus, the product can be used for Fischer-Tropsch synthesis. The results of a series of experiments and X-ray photoelectron spectroscopy analysis showed that the synergy between the C N and Fe N groups in the catalyst can promote the reduction of CO2 to CO. This work demonstrates a facile method for improving the catalytic reduction of CO2.

The conversion of CO2 electrocatalytic hydrogenation into energy-rich fuel is considered to be the most effective way to carbon recycle. Nitrogen-doping carbonized ZIF-8 is proposed as carrier of the earth-rich Sn catalyst to overcome the limit of electron transfer and CO2 adsorption capacity of Sn. Hierarchically porous structure of Sn doped carbonized ZIF-8 is controlled by hydrothermal and carbonization conditions, which induces much higher specific surface area than that of the commercial Sn nanoparticle (1003.174 vs. 7.410 m2·g-1). The shift of nitrogen peaks in X-ray Photoelectron Spectroscopy spectra indicates interaction between ZIF-8 and Sn, which induces the shift of electron cloud from Sn to the chemical nitrogen to enhance conductivity and regulate electron transfer from catalyst to CO2. Lower mass transfer resistance and Warburg resistance are investigated through EIS, which significantly improves the catalytic activity for CO2 reduction reaction (CO2RR). Onset potential of the reaction is reduced from -0.74 V to less than -0.54 V vs. RHE. The total Faraday efficiency of HCOOH and CO reaches 68.9 % at -1.14 V vs. RHE, which is much higher than that of the commercial Sn (45.0 %) and some other Sn-based catalyst reported in the literature.

Design of efficient catalysts for electrochemical reduction of carbon dioxide (CO2) with high selectivity and activity is of great challenge, but significant for managing the global carbon balance. Herein, a series of three-dimensional (3D) single-atom metals anchored on graphene networks (3D SAM-G) with open-pore structure were successfully mass-produced via a facile in-situ calcination technique assisted by NaCl template. As-obtained 3D SANi-G electrode delivers excellent CO Faradaic efficiency (FE) of >96% in the potential range of −0.6 to −0.9 V versus reversible hydrogen electrode (RHE) and a high current density of 66.27 mA cm−2 at −1.0 V versus RHE, outperforming most of the previously reported catalysts tested in H-type cells. Simulations indicate that enhanced mass transport within the 3D open-pore structure effectively increases the catalytically active sites, which in turn leads to simultaneous enhancement on selectivity and activity of 3D SANi-G toward CO2 electroreduction. The cost-effective synthesis approach together with the microstructure design concept inspires new insights for the development of efficient electrocatalysts.

Electrochemical carbon dioxide reduction (CO2R) provides a promising pathway for sustainable generation of fuels and chemicals. Copper (Cu) electrocatalysts catalyse CO2R to valuable multicarbon (C2+) products, but their selectivity depends on the local microenvironment near the catalyst surface. Here we systematically explore and optimize this microenvironment using bilayer cation- and anion-conducting ionomer coatings to control the local pH (via Donnan exclusion) and CO2/H2O ratio (via ionomer properties), respectively. When this tailored microenvironment is coupled with pulsed electrolysis, further enhancements in the local ratio of CO2/H2O and pH are achieved, leading to selective C2+ production, which increases by 250% (with 90% Faradaic efficiency and only 4% H2) compared with static electrolysis over bare Cu. These results underscore the importance of tailoring the catalyst microenvironment as a means of improving overall performance in electrochemical syntheses. Copper catalyses electrochemical reduction of CO2 to valuable multicarbon products, but its selectivity depends on the local microenvironment near the catalyst surface. Here, the authors explore and optimize this environment to improve performance using bilayer ionomer coatings to control the local pH and CO2/H2O ratio.

In the face of the increasingly serious greenhouse effect and climate warming, carbon dioxide reduction (CO2RR) technology, which can produce valuable chemicals and fuels while consuming CO2, has b...

The reaction chemistry of both silanes and hydrogen at para-terphenyl diphosphine-supported molybdenum complexes was explored within the context of carbon dioxide (CO₂) reduction. CO₂ hydrosilylation commonly affords reduction products via silyl acetals. However, while silyl hydride complexes were characterized in the present system, synthetic, spectroscopic, and kinetic studies suggest C–O cleavage of CO₂ occurs independently of silanes. In their presence, a putative molybdenum oxo intermediate is hypothesized to undergo O-atom transfer, yielding silanol. In contrast, hydrogenation chemistry does occur through an intermediate molybdenum dihydride capable of inserting CO₂ to yield a formate hydride complex. This process is reversible; slow deinsertion under dinitrogen affords a mixture of molybdenum dihydride, η²-CO₂, and N₂ complexes. The molybdenum hydride formate species is a competent precatalyst for both CO₂ hydrogenation to formate (in the presence of lithium cations and base) and formic acid dehydrogenation to CO₂ and hydrogen (in the presence of base). Mechanistic studies of both catalytic processes are presented.

Electrochemical reduction of carbon dioxide (CO 2 ) into chemicals and fuels has recently attracted much interest, but normally suffers from a high overpotential and low selectivity. In this work, single P atoms were introduced into a N-doped carbon supported single Fe atom catalyst (Fe- SAC /NPC) mainly in the form of P-C bonds for CO 2 electroreduction to CO in an aqueous solution. This catalyst exhibited a CO Faradaic efficiency of ~97% at a low overpotential of 320 mV, and a Tafel slope of only 59 mV dec -1 , comparable to state-of-the-art gold catalysts. Experimental analysis combined with DFT calculations suggested that single P atom in high coordination shells (n ≥ 3), in particular the third coordination shell of Fe center enhanced the electronic localization of Fe, which improved the stabilization of the key *COOH intermediate on Fe, leading to superior CO 2 electrochemical reduction performance at low overpotentials.

Summary Electrochemical reduction of carbon dioxide (CO2RR) converts intermittent renewable energy into high energy density fuels, such as ethanol. Membrane electrode assembly (MEA) electrolyzers are particularly well-suited for CO2-to-ethanol conversion in view of their low ohmic resistance and high stability. However, over 75% of the ethanol produced at the cathode migrates through the membrane where it is diluted by the anolyte and may be oxidized. The ethanol concentration that results is two orders of magnitude below the 10 wt % standard set by the incumbent industrial process, fermentation. Here, we reverse the direction of ion and electroosmotic transport by means of a porous proton exchange layer, thereby blocking both the convective and diffusive routes of ethanol loss. With this strategy, we eliminate ethanol crossover to the anode (

Metal-carbon matrix catalyst has attracted a great deal of interest in electrochemical carbon dioxide reduction reaction (CO2RR) due to its excellent electrocatalytic performance. However, the design of highly active metal–carbon matrix catalyst towards CO2RR using natural biomass and cheap chemical precursors is still under challenge. Herein, a self-assembly strategy, along with CO2 gas as acidifying agent, to fabricate silk fibroin (SF) derived carbon aerogels (CA) combining trace copper nanoparticles (SF-Cu/CA) is developed. Zinc nitrate was introduced as a pore-forming agent to further optimize the pore structure of the as-prepared catalysts to form SF-Cu/CA-1. The rich mesoporous structure and unique constitute of SF-Cu/CA-1 is conducive to exposed numerous active sites, fast electron transfer rate, and the desorption of *CO intermediate, thus leading to the electrocatalytic CO2RR of SF-Cu/CA-1 catalyst with an excellent current density of 29.4 mA cm−2, Faraday efficiency of 83.06% towards carbon monoxide (CO), high the ratio value of CO/H2 (19.58), and a long-term stability over a 10-hour period. This performance is superior to that of SF-Cu/CA catalyst (13.0 mA cm−2, FE CO =58.43%, CO/H2 = 2.16). This work not only offers a novel strategy using natural biomass and cheap chemicals to build metal–carbon matrix catalyst for electrocatalytic CO2-to-CO conversion, but also is expected to promote the industrial-scale implementations of CO2 electroreduction.

The local pH near the surface of a CO₂ reduction electrocatalyst strongly impacts catalytic selectivity and activity. Here, confocal fluorescence microscopy was used to map the electrolyte pH near a copper gas diffusion electrode during CO₂ reduction with micron spatial resolution in three dimensions. We observed that the local pH increased from pH 6.8 to greater than pH 10 as the current density was increased from 0 to 28 mA/cm² in a 100 mM KHCO₃ electrolyte. Variations in the pH across the surface indicate areas of locally increased activity. Within deep trenches of the active layer, the local pH increases as trench width decreases. Computational models confirm these experimental results and also showed that the catalyst found within narrow trenches is more active than that found at the surface of the electrode. This study suggests that the overpotential required to perform selective CO₂ reduction can be reduced by increasing the density of narrow trench regions in the microporous layer.

An effective Ru/CNT electrocatalyst plays a crucial role in solid-state lithium-carbon dioxide batteries. In the present article, ruthenium metal decorated on a multi-walled carbon nanotubes (CNTs) is introduced as a cathode for the lithium-carbon dioxide batteries with Li1.5Al0.5Ge1.5(PO4)3 solid-state electrolyte. The Ru/CNT cathode exhibits a large surface area, maximum discharge capacity, excellent reversibility, and long cycle life with low overpotential. The electrocatalyst achieves improved electrocatalytic performance for the carbon dioxide reduction reaction and carbon dioxide evolution reaction, which are related to the available active sites. Using the Ru/CNT cathode, the solid-state lithium-carbon dioxide battery exhibits a maximum discharge capacity of 4541 mA h g-1 and 45 cycles of battery life with a small voltage gap of 1.24 V compared to the CNT cathode (maximum discharge capacity of 1828 mA h g-1, 25 cycles, and 1.64 V as voltage gap) at a current supply of 100 mA g-1 with a cutoff capacity of 500 mA h g-1. Solid-state lithium-carbon dioxide batteries have shown promising potential applications for future energy storage.

Electrochemical carbon dioxide reduction reaction (CO2RR) has been investigated for decades. CO2RR to value-added products is an indispensable option to address climate change and energy storage needs. We believed that CO2RR performance can be influenced by the anode materials employed for the oxidation half-reaction. Although H2O oxidation near-neutral solution does not being received greater attention, there is also an idea that it plays an important role not only in completing CO2reduction cycle, but also to significantly influence the cathode during reduction. Therefore, the present study aimed to investigate the impact of three different anode materials (platinum, glassy carbon, and hematite) on the activity and selectivity of the gold cathode in an electrochemical CO2reduction reaction. Linear sweep voltammetry and electrochemical impedance spectroscopy have been used to study electrocatalytic properties. In the meantime, x-ray diffraction is used to investigate the crystal planes of the as-prepared electrodes, while the work function and morphology of Au films were measured by atomic force microscope. Similar activity and selectivity to CO formation were observed when platinum and hematite were used as counter electrodes, while the least CO formation was recorded on the glassy carbon counter electrode.Graphic abstractThe protons (H+) obtained from the oxidation of H2O onto these three different anodic materials (platinum, glassy carbon, hematite) are moving faster through the bulk of the solution to the working electrode. Consequently, the reaction occurred on the working electrode can be influenced by the number of protons coming from the anode.

Calcium and strontium tantalates with general formula A2Ta2O7 (A = Ca, Sr) were prepared by the solid-state synthesis and evaluated in the photocatalytic water splitting and CO2 reduction. A predominance in the water splitting processes is observed in both materials obtaining competitive yields for H2 and O2 compared to the results reported in the literature. A better performance was observed in the Sr2Ta2O7 sample associated with its crystalline structure and morphology (H2 = 807 μmol g−1, O2 = 296 μmol g−1, CO = 5 μmol g−1 for 6 h). Besides, both materials were decorated with Co3O4 and CuO particles acting as cocatalysts. The presence of these oxides enhanced the evolution of the products considerably due to the efficient charges transport avoiding their recombination, being the Co3O4 loaded sample the most efficient in both cases. The presence of CuO favored the formation of CO in both tantalate materials; however, their rates are not comparable with the obtained for H2 and O2, being the water-splitting process also predominant with the use of both cocatalysts.

The utilization of carbon dioxide as a resource through electrocatalysis is one of the ideal ways to alleviate or solve the current ecological crisis mankind facing. The development of inexpensive and efficient catalysts is the key to promoting the industrialization of electrocatalytic carbon dioxide reduction. CO is an important industrial raw material, as a result, CO2 reduction to CO has important research significance. However, high-active noble metal catalysts that can convert CO2 to CO are difficult to apply in large scale. Zn-based catalysts are potential substitutes. However, the reduction activity of Zn-based catalysts still can not meet the actual needs. In this paper, ZnOHF material is employed in the electrocatalytic CO2 reduction for the first time. ZnOHF nanorods of different sizes are prepared through a simple hydrothermal synthesis method and tested in a Flow-Cell. The large specific surface area of the nanorods and the existence of F atoms on the surface of the material lead to good catalytic activity. The Flow-Cell accelerates the reaction mass transfer process. At −1.28V (vs. RHE), the R2-ZnOHF nanorods have the highest CO Faraday efficiency of 76.4% with the CO current density of 57.53 mA/cm2.

Single-atom catalysts (SACs), as a novel emerging category in heterogeneous catalysis, have exhibited superb activity and selectivity within the scope of many catalytic reactions, originating from their nature of atomic dispersion. However, they are not appropriate for more complicated reactions that benefit from multi-metal promotion, such as the carbon dioxide reduction reaction (CO2 RR). Atomic pair catalysts can provide a synergistic effect to break the intrinsic activity limit. Herein, inspired by theoretical prediction, a hetero-paired atomic-site catalyst (Ni/Fe-N/O-C) was developed for CO2 RR. Typically, the trace-amount-loaded double-atom-site catalysts exhibited outstanding turnover frequencies (≈460 s-1 ) surpassing reported ones by far. Interestingly, the loaded metal contents of the three M-N/O-C samples were extremely low, and Ni/Fe-N/O-C exhibited greatly improved durability compared with pure Ni-N/O-C or Fe-N/O-C and excellent CO selectivity above 80 % within a broad potential window of -1.4 to -1.7 V (vs. saturated calomel electrode, 99.8 % at -1.5 V). The superb performance of diatomic-site catalysts was attributed to the adjusted local environment and electron structure of the active center, which could decrease the reaction barrier of *COOH formation. This work presents new insights into manipulating electrocatalytic performance for the development of more sophisticated active sites.

Electrocatalysis, as the nexus for energy storage and environmental remediation, requires developing low-cost and high-performing heterogeneous catalysts. Compared with the single atom catalysts (SACs), dual-atom catalysts (DACs) are attracting ever-increasing interest due to their higher metal loading, more versatile active sites and unique reactivity. However, controlled synthesis of DACs remains a great challenge, and their electrocatalytic applications are still in infancy. This review first discusses the synthesis of DACs by highlighting several synthetic strategies. Subsequently, we exemplify the unique reactivities of DACs in electrocatalytic applications including water splitting, oxygen reduction, carbon dioxide reduction and nitrogen reduction. The structure-activity relations of DACs are specifically discussed in comparison with that of SACs, on the basis of experimental and theoretical studies. Finally, the opportunities and challenges of DACs are summarized in terms of rational design, controlled synthesis, characterization, and applications.

Among the various types of metal organic frameworks (MOFs), the metal-oxide-based ones fulfill all the essential criteria such as strong bonding, organic linking units, and highly crystalline nature, properties required to be effective photocatalysts to serve environmental remediation. Moreover, the even spread of active sites and semiconductor properties make the MOFs ideal for absorbing irradiation from UV as well as visible light sources. Metal oxide composites with carbon based materials, especially, show high photocatalytic activity toward the degradation of organic dyes. Considering the relatively low cost of metal oxide semiconductors compared to pure metallic nanoparticles, metal oxide composites can provide a great alternative as photocatalysts especially considering the adjustable bandgaps and synergistic effects. Therefore, the metal oxide application as the photocatalysts in industry and technology in terms of techno-economic advantage is attracted. In this study, energy sustainability and solving carbon-related issues through metal oxide-based materials are discussed. This study aims to review metal oxide composites including metal oxide-MOFs and metal oxide-carbon material compositions as photocatalysts, application, merits in environmental and energy systems performances, and its contribution as an influential factor for sustainable development.

Carbon dioxide (CO2) is one of the main causes of global warming, with the burning of fossil fuels being the main source of anthropogenic CO2. For this reason, the capture and reduction of CO2 to v...

King Abdullah University of Science and Technology is gratefully acknowledged for financial support.

Electrochemical CO2 reduction provides a promising strategy to product value-added fuels and chemical feedstocks. However, it remains a grand challenge to further reduce the overpotentials and increase current density for large-scale applications. Here, spontaneously Sn doped Bi/BiOx nanowires (denoted as Bi/Bi(Sn)Ox NWs) with a core-shell structure were synthesized by an electrochemical dealloying strategy. The Bi/Bi(Sn)Ox NWs exhibit impressive formate selectivity over 92% from -0.5 to -0.9 V versus reversible hydrogen electrode (RHE) and achieve a current density of 301.4 mA cm-2 at -1.0 V vs RHE. In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiOx species can promote the stabilization of the *OCHO intermediate on the Bi(Sn)Ox surface and suppress the competitive H2/CO production. This work provides effective in situ construction of the metal/metal oxide hybrid composites with heteroatom doping and new insights in promoting electrochemical CO2 conversion into formate for practical applications.