Electrocatalytic reduction of carbon dioxide to carbon monoxide and methane at an immobilized cobalt protoporphyrin

Enhancing CO2 Electrocatalysis on 2D Porphyrin-Based Metal-Organic Framework Nanosheets Coupled with Visible-Light

2D catalysts combined with single atom sites are promising candidates to promote CO₂ reduction performance, but the ability to target stable materials with distinct structure still remains challenging. Herein, a series of single metal atoms anchored 2D metal-organic framework nanosheets (MOF-NS-M) with visualized and well-ordered mesoporous structures are fabricated and exhibit enhanced CO₂ reduction activity and selectivity with the assistance of visible-light. Encouragingly, the CO Faradaic efficiency of MOF-NS-Co exceeds 90% in a wide potential window of -0.5 to -1.0 V versus RHE and reaches 98.7% with 100 mV positive shift compared with the result measured under dark. The catalytic kinetics studies show a fast initial electron transfer to CO₂ to form *COO^- , thanks to the sufficient exposed active sites resulting from the nanosheet nature and adjusted electron transfer pathway caused by the porphyrin photoswitch.

Recent Developments in Metalloporphyrin Electrocatalysts for Reduction of Small Molecules: Strategies for Managing Electron and Proton Transfer Reactions

Porphyrins are archetypal ligands in inorganic chemistry. The last 10 years have seen important new advances in the use of metalloporphyrins as catalysts in the activation and reduction of small molecules, in particular O₂ and CO₂ . Recent developments of new molecular designs, scaling relationships, and theoretical modeling of mechanisms have rapidly advanced the utility of porphyrins as electrocatalysts. This Minireview focuses on the summary and evaluation of recent developments of metalloporphyrin O₂ and CO₂ reduction electrocatalysts, with an emphasis on contrasting homogeneous and heterogeneous electrocatalysis. Comparisons for proposed reaction mechanisms are provided for both CO₂ and O₂ reduction, and ideas are proposed about how lessons from the last decade of research can lead to the development of practical, applied porphyrin-derived catalysts.

Electropolymerized metal-protoporphyrin electrodes for selective electrochemical reduction of CO2

Developing catalysts that exhibit high efficiencies for the electrochemical CO₂ reduction reaction (CO₂RR) in aqueous media is vital both for a healthier environment and practical implementation to produce value-added fuels from energy waste.

Suppression of Hydrogen Evolution in Acidic Electrolytes by Electrochemical CO2 Reduction

In this article we investigate the electrochemical reduction of CO₂ at gold electrodes under mildly acidic conditions. Differential electrochemical mass spectroscopy (DEMS) is used to quantify the amounts of formed hydrogen and carbon monoxide as well as the consumed amount of CO₂. We investigate how the Faradaic efficiency of CO formation is affected by the CO₂ partial pressure (0.1-0.5 bar) and the proton concentration (1-0.25 mM). Increasing the former enhances the rate of CO₂ reduction and suppresses hydrogen evolution from proton reduction, leading to Faradaic efficiencies close to 100%. Hydrogen evolution is suppressed by CO₂ reduction as all protons at the electrode surfaces are used to support the formation of water (CO₂ + 2H⁺ + 2e^- → CO + H₂O). Under conditions of slow mass transport, this leaves no protons to support hydrogen evolution. On the basis of our results, we derive a general design principle for acid CO₂ electrolyzers to suppress hydrogen evolution from proton reduction: the rate of CO/OH^- formation must be high enough to match/compensate the mass transfer of protons to the electrode surface.

DFT and Empirical Considerations on Electrocatalytic Water/Carbon Dioxide Reduction by CoTMPyP in Neutral Aqueous Solutions*

A combined experimental and density functional theory (DFT) investigation was employed in order to examine the mechanism of electrochemical CO₂ reduction and H₂ formation from water reduction in neutral aqueous solutions. A water soluble cobalt porphyrin, cobalt [5,10,15,20-(tetra-N-methyl-4-pyridyl)porphyrin], (CoTMPyP), was used as catalyst. The possible attachment of different axial ligands as well as their effect on the electrocatalytic cycles were examined. A cobalt porphyrin hydride is a key intermediate which is generated after the initial reduction of the catalyst. The hydride is involved in the formation of H₂ and formate and acts as an indirect proton source for the formation of CO in these H⁺ -starving conditions. The experimental results are in agreement with the computations and give new insights into electrocatalytic mechanisms involving water soluble metalloporphyrins. We conclude that in addition to the porphyrin's structure and metal ion center, the electrolyte surroundings play a key role in dictating the products of CO₂ /H₂ O reduction.

Nanostructured Cobalt-Based Electrocatalysts for CO2 Reduction: Recent Progress, Challenges, and Perspectives

CO₂ reduction reaction (CO₂ RR) provides a promising strategy for sustainable carbon fixation by converting CO₂ into value-added fuels and chemicals. In recent years, considerable efforts are focused on the development of transition-metal (TM)-based catalysts for the selectively electrochemical CO₂ reduction reaction (ECO₂ RR). Co-based catalysts emerge as one of the most promising electrocatalysts with high Faradaic efficiency, current density, and low overpotential, exhibiting excellent catalytic performance toward ECO₂ RR for CO and HCOOH productions that are economically viable. The intrinsic contribution of Co and the synergistic effects in Co-hybrid catalysts play essential roles for future commercial productions by ECO₂ RR. This review summarizes the rational design of Co-based catalysts for ECO₂ RR, including molecular, single-metal-site, and oxide-derived catalysts, along with the nanostructure engineering techniques to highlight the distribution of the ECO₂ RR products by Co-based catalysts. The density functional theory (DFT) simulations and advanced in situ characterizations contribute to interpreting the synergies between Co and other materials for the enhanced product selectivity and catalytic activity. Challenges and outlook concerning the catalyst design and reaction mechanism, including the upgrading of reaction systems of Co-based catalysts for ECO₂ RR, are also discussed.

Vitamin B12-Immobilized Graphene Oxide for Efficient Electrocatalytic Carbon Dioxide Reduction Reaction

A naturally occurring water-soluble cobalt-complex cyanocobalamin (Vitamin B12) has been identified as a new and efficient electrocatalyst for the CO₂ -to-CO reduction reaction in aqueous solution. Heterogeneous B12-electrocatalysts prepared by a simple electrochemical immobilization technique on graphene-oxide (GO)-modified glassy carbon and carbon paper (CP) electrodes, without any non-degradable polymer-binders, showed a highly stable and well-defined surface-confined redox peak at E'=-0.138 V vs. RHE with a surface-excess value, Γ_B12 =4.28 nmol cm^-2 . This new electrocatalyst exhibits 93 % Faradaic efficiency for CO₂ -to-CO conversion at an electrolysis potential, -0.882 V vs. RHE (an optimal condition) with a high current density, 29.4 mA cm^-2 and turn-over-frequency value, 5.2 s^-1 , without any surface-fouling problem, in 0.5 m KHCO₃ . In further, it follows an eco-friendly, sustainable and water-based approach with the involvement of biodegradable and non-toxic chemicals/materials like B12, GO and CP.

Efficient Carbon Dioxide Electroreduction over Ultrathin Covalent Organic Framework Nanolayers with Isolated Cobalt Porphyrin Units

Electrochemical CO₂ reduction represents a sustainable approach for the conversion of CO₂ into valuable fuels and chemicals. Here, we fabricated a series of composite nanomaterials through template-oriented polymerization of covalent organic frameworks (COFs) with isolated cobalt porphyrin units on amino-functionalized carbon nanotubes for efficient electrocatalytic CO₂ reduction reaction (CO₂RR). Compared with pure COFs, the hybrid form of ultrathin COF nanolayers wrapped on the conductive scaffold leads to distended current density and stable Faradaic efficiency for CO₂-to-CO conversion over a wide potential range. Specifically, the catalytic performances of the system can be finely optimized by the modification of the reticular structure with different functional groups. Our work gives a new strategy for the preparation of highly active and selective electrocatalysts for CO₂RR.

Electrochemical Conversion of CO2 to CO by a Competent FeI Intermediate Bearing a Schiff Base Ligand

Iron complexes with a N₂ O₂ -type N,N'-bis(salicylaldehyde)-1,2-phenylenediamine salophen ligand catalyze the electrochemical reduction of CO₂ to CO in acetonitrile with phenol as the proton donor, giving rise to 90-99 % selectivity, faradaic efficiency up to 58 %, and turnover frequency up to 10³  s^-1 at an overpotential of 0.65 V. This novel class of molecular catalyst for CO₂ reduction operate through a mononuclear Fe^I intermediate, with phenol being involved in the process with first-order kinetics. The molecular nature of the catalyst and the low cost, easy synthesis and functionalization of the salophen ligand paves the way for catalyst engineering and optimization. Competitive electrodeposition of the coordination complex at the electrode surface results in the formation of iron-based nanoparticles, which are active towards heterogeneous electrocatalytic processes mainly leading to proton reduction to hydrogen (faradaic efficiency up to 80 %) but also to the direct reduction of CO₂ to methane with a faradaic efficiency of 1-2 %.

Molecular catalysis of CO2 reduction: recent advances and perspectives in electrochemical and light-driven processes with selected Fe, Ni and Co aza macrocyclic and polypyridine complexes

Earth-abundant Fe, Ni, and Co aza macrocyclic and polypyridine complexes have been thoroughly investigated for CO2 electrochemical and visible-light-driven reduction. Since the first reports in the 1970s, an enormous body of work has been accumulated regarding the two-electron two-proton reduction of the gas, along with mechanistic and spectroscopic efforts to rationalize the reactivity and establish guidelines for structure-reactivity relationships. The ability to fine tune the ligand structure and the almost unlimited possibilities of designing new complexes have led to highly selective and efficient catalysts. Recent efforts toward developing hybrid systems upon combining molecular catalysts with conductive or semi-conductive materials have converged to high catalytic performances in water solutions, to the inclusion of these catalysts into CO2 electrolyzers and photo-electrochemical devices, and to the discovery of catalytic pathways beyond two electrons. Combined with the continuous mechanistic efforts and new developments for in situ and in operando spectroscopic studies, molecular catalysis of CO2 reduction remains a highly creative approach.

Selective single-atom electrocatalysts: a review with a focus on metal-doped covalent triazine frameworks

Single-atom electrocatalysts (SACs), which comprise singly isolated metal sites supported on heterogeneous substrates, have attracted considerable recent attention as next-generation electrocatalysts for various key reactions from the viewpoint of the environment and energy. Not only electrocatalytic activity but also selectivity can be precisely tuned via the construction of SACs with a defined coordination structure, such as homogeneous organometallics. Covalent organic frameworks (COFs) are promising supports for single-atom sites with designed coordination environments due to their unique physicochemical properties, which include porous structures, robustness, a wide range of possible designs, and abundant heteroatoms to coordinate single-metal sites. The rigid frameworks of COFs can hold unstable single-metal atoms, such as coordinatively unsaturated sites or easily aggregated Pt-group metals, which exhibit unique electrocatalytic selectivity. This minireview summarizes recent advances in the selective reactions catalysed by SACs, mainly those supported on triazine-based COFs.

Single-atom electrocatalysts (SACs) have attracted considerable attention as selective electrocatalysts. Metal-doped covalent triazine frameworks will be a novel platform for selective SACs to solve energy and environmental issues.

In Situ Scanning Tunneling Microscopy of Cobalt-Phthalocyanine-Catalyzed CO2 Reduction Reaction

We report a molecular investigation of a cobalt phthalocyanine (CoPc)-catalyzed CO₂ reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO₂ -purged electrolyte environment. The ECSTM experiments indicate the proportion of high-contrast species correlated with the reduction of Co^II Pc (-0.2 V vs. saturated calomel electrode (SCE)). The high-contrast species is ascribed to the CoPc-CO₂ complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc-CO₂ to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO₂ , and the latter is the rate-limiting step. The rate constant of the formation and dissociation of CoPc-CO₂ is estimated on the basis of the in situ ECSTM experiment.

Organic-Inorganic Hybrid Nanomaterials for Electrocatalytic CO2 Reduction

Electrochemical CO₂ reduction (ECR) to value-added chemicals and fuels is regarded as an effective strategy to mitigate climate change caused by CO₂ from excess consumption of fossil fuels. To achieve CO₂ conversion with high faradaic efficiency, low overpotential, and excellent product selectivity, rational design and synthesis of efficient electrocatalysts is of significant importance, which dominates the development of ECR field. Individual organic molecules or inorganic catalysts have encountered a bottleneck in performance improvement owing to their intrinsic shortcomings. Very recently, organic-inorganic hybrid nanomaterials as electrocatalysts have exhibited high performance and interesting reaction processes for ECR due to the integration of the advantages of both heterogeneous and homogeneous catalytic processes, attracting widespread interest. In this work, the recent advances in designing various organic-inorganic hybrid nanomaterials at the atomic and molecular level for ECR are systematically summarized. Particularly, the reaction mechanism and structure-performance relationship of organic-inorganic hybrid nanomaterials toward ECR are discussed in detail. Finally, the challenges and opportunities toward controlled synthesis of advanced electrocatalysts are proposed for paving the development of the ECR field.

Electrocatalytic Reduction of CO2 to Ethylene by Molecular Cu-Complex Immobilized on Graphitized Mesoporous Carbon

The electrochemical reduction of carbon dioxide (CO₂ ) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO₂ to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO₂ to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO₂ in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.

Electroreduction of CO2 in Ionic Liquid-Based Electrolytes

Electroreduction of carbon dioxide (CO₂) to value-added chemicals and fuels is a promising approach for sustainable energy conversion and storage. Many electrocatalysts have been designed for this purpose and studied extensively. The role of the electrolyte is particularly interesting and is pivotal for designing electrochemical devices by taking advantage of the synergy between electrolyte and catalyst. Recently, ionic liquids as electrolytes have received much attention due to their high CO₂ adsorption capacity, high selectivity, and low energy consumption. In this review, we present a comprehensive overview of the recent progress in CO₂ electroreduction in ionic liquid-based electrolytes, especially in the performance of different catalysts, the electrolyte effect, as well as mechanism studies to understand the reaction pathway. Perspectives on this interesting area are also discussed for the construction of novel electrochemical systems.

Selective electrochemical reduction of carbon dioxide to ethanol via a relay catalytic platform

Efficient electroreduction of carbon dioxide (CO2) to ethanol is of great importance, but remains a challenge because it involves the transfer of multiple proton-electron pairs and carbon-carbon coupling. Herein, we report a CoO-anchored N-doped carbon material composed of mesoporous carbon (MC) and carbon nanotubes (CNT) as a catalyst for CO2 electroreduction. The faradaic efficiencies of ethanol and current density reached 60.1% and 5.1 mA cm-2, respectively. Moreover, the selectivity for ethanol products was extremely high among the products produced from CO2. A proposed mechanism is discussed in which the MC-CNT/Co catalyst provides a relay catalytic platform, where CoO catalyzes the formation of CO* intermediates which spill over to MC-CNT for carbon-carbon coupling to form ethanol. The high selectivity for ethanol is attributed mainly to the highly selective carbon-carbon coupling active sites on MC-CNT.

Manifesto for the routine use of NMR for the liquid product analysis of aqueous CO2 reduction: from comprehensive chemical shift data to formaldehyde quantification in water

CO2 reduction research is at a critical turnaround since it has the potential to partially or even substantially fulfil future clean energy needs. CO2-to-CO electrochemical conversion is getting closer from industrial implementation requirements. Efforts are now more and more directed to obtain highly reduced products such as methanol, methane, ethylene, ethanol, etc., most of them being liquids. Gas-phase products (e.g., CO, CH4) are typically detected and quantified by well-defined gas chromatography (GC and GC/MS) protocols. On the other hand, NMR, GC-MS, HPLC have been used for the liquid phase characterization, but no routine technique has yet been established, mainly due to lack of versatility of a single technique. Additionally, except NMR and GC-MS, classical techniques cannot distinguish 13C from 12C products, although it is a mandatory step to assess products origin. Herein, we show the efficiency and applicability of 1H NMR as routine technique for liquid phase products analysis and we address two previous shortcomings. We first established a comprehensive 1H and 13C NMR chemical shifts list for all 12CO2 and 13CO2 reduction products in water ranging from C1 to C3. Then we overcame the difficulty of identifying aqueous formaldehyde intermediate by 1H NMR through an efficient chemical trapping step, along with isotopic signature study. Formaldehyde can be reliably quantified in water with a concentration as low as 50 μM.

Analysis of Research Status of CO2 Conversion Technology Based on Bibliometrics

The concentration of carbon dioxide in the air has risen sharply due to the use of fossil fuels, causing environmental problems such as the greenhouse effect, which seriously threatens humans’ living environment. Reducing carbon dioxide emissions while addressing energy shortages requires the conversion of CO2 into high added-value products. In this paper, the status of CO2 conversion research in the past ten years is analyzed using the bibliometric method; the influence of countries and institutions, journal article statistics and other aspects are statistically analyzed, and the research status of carbon dioxide catalytic conversion is briefly introduced. Finally, according to the analysis results and the existing problems of CO2 catalytic conversion research, the future development direction of CO2 catalytic conversion research is prospected.

Synthesis of Crystalline Silica-Carbonate Biomorphs of Ba(II) under the Presence of RNA and Positively and Negatively Charged ITO Electrodes: Obtainment of Graphite via Bioreduction of CO2 and Its Implications to the Chemical Origin of Life on Primitive Earth

Since Earth was formed, in the Precambrian era up until our present days, electric current has participated in the morphology and chemical composition of organic and inorganic structures. Attempting to elucidate the mechanism by which electric current participated in the creation of the first cell in the Precambrian era is an intriguing and of a permanent subject of interest to be studied. One way of emulating the formation of structures similar to those that might have existed in the Precambrian era in the presence of a biomolecule and an electric current source is to use as a model, the silica-carbonate of alkaline earth metal compounds known as biomorphs. The objective of this work was to assess the influence exerted by an electric current (negatively or positively charged indium tin oxide electrodes) on the formation of biomorphs in the presence of RNA. The compounds obtained under both electric charges were visualized through scanning electron microscopy (SEM), and their chemical composition was analyzed through Raman spectroscopy. The biomorphs obtained under a positive electric current correspond to aragonite-type BaCO₃(I) and calcite-type BaCO₃(II). Whereas, under a negative current, carbon graphite and aragonite-type BaCO₃(I) were obtained. To the best of our knowledge, this is the first evidence showing that the presence of RNA and the electric current is fundamental in the rearrangement of atoms, suggesting that organic and inorganic compounds have coexisted since the primitive era.

Recent advances in metalloporphyrin-based catalyst design towards carbon dioxide reduction: from bio-inspired second coordination sphere modifications to hierarchical architectures

Research in the development of new molecular catalysts for the selective transformation of CO2 to reduced forms of carbon is attracting enormous interest from chemists. Molecular catalyst design hinges on the elaboration of ligand scaffolds to manipulate the electronic and structural properties for the fine tuning of the reactivity pattern. A cornucopia of ligand sets have been designed along this line and more and more are being reported. In this quest, the porphyrin molecular platform has been under intensive focus due to the unmatched catalytic properties of metalloporphyrins. There have been rapid advances in this particular field during the last few years wherein both electronic and structural aspects in the second coordination spheres have been addressed to shift the overpotential and improve the catalytic rates and product selectivity. Metalloporphyrins have also attracted much attention in terms of the elaboration of hybrid materials for heterogeneous catalysis. Here too, some promising activities have made metalloporphyrin derivatives serious candidates for technological implementation. This review collects the recent advances centred around the chemistry of metalloporphyrins for the reduction of CO2.

Two-dimensional metal-organic frameworks and their derivatives for electrochemical energy storage and electrocatalysis

Two-dimensional (2D) metal-organic frameworks (MOFs) and their derivatives with excellent dimension-related properties, e.g. high surface areas, abundantly accessible metal nodes, and tailorable structures, have attracted intensive attention as energy storage materials and electrocatalysts. A major challenge on the road toward the commercialization of 2D MOFs and their derivatives is to achieve the facile and controllable synthesis of 2D MOFs with high quality and at low cost. Significant developments have been made in the synthesis and applications of 2D MOFs and their derivatives in recent years. In this review, we first discuss the state-of-the-art synthetic strategies (including both top-down and bottom-up approaches) for 2D MOFs. Subsequently, we review the most recent application progress of 2D MOFs and their derivatives in the fields of electrochemical energy storage (e.g., batteries and supercapacitors) and electrocatalysis (of classical reactions such as the HER, OER, ORR, and CO2RR). Finally, the challenges and promising strategies for the synthesis and applications of 2D MOFs and their derivatives are addressed for future development.

Electrochemical CO2 Reduction to CO Catalyzed by 2D Nanostructures

Electrochemical CO2 reduction towards value-added chemical feedstocks has been extensively studied in recent years to resolve the energy and environmental problems. The practical application of electrochemical CO2 reduction technology requires a cost-effective, highly efficient, and robust catalyst. To date, vigorous research have been carried out to increase the proficiency of electrocatalysts. In recent years, two-dimensional (2D) graphene and transition metal chalcogenides (TMCs) have displayed excellent activity towards CO2 reduction. This review focuses on the recent progress of 2D graphene and TMCs for selective electrochemical CO2 reduction into CO.

Carbon-Nanotube-Supported Copper Polyphthalocyanine for Efficient and Selective Electrocatalytic CO2 Reduction to CO

Electroreduction of CO₂ to CO is one of the simplest ways to valorise CO₂ as a source of carbon. Herein, a cheap, robust, Cu-based hybrid catalyst consisting of a polymer of Cu phthalocyanine coated on carbon nanotubes, which proved to be selective for CO production (80 % faradaic yield) at relatively low overpotentials, was developed. Polymerisation of Cu phthalocyanine was shown to have a drastic effect on the selectivity of the reaction because molecular Cu phthalocyanine was instead selective for proton reduction under the same conditions. Although the material only showed isolated Cu sites in phthalocyanine-like CuN₄ coordination, in situ and operando X-ray absorption spectroscopy showed that, under operating conditions, the Cu atoms were fully converted to Cu nanoparticles, which were likely the catalytically active species. Interestingly, this restructuring of the metal sites was reversible.

Covalently anchoring cobalt phthalocyanine on zeolitic imidazolate frameworks for efficient carbon dioxide electroreduction

Transformation of CO₂ into fuels has drawn great attention due to increasing carbon emission in recent years.

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst

Selective photocatalytic reduction of CO₂ has been regarded as one of the most amazing ways for re-using CO₂. However, its application is still limited by the low CO₂ conversion efficiency. This work developed a novel Pt/In₂O₃/g-C₃N₄ multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO₂ reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In₂O₃ and g-C₃N₄ acted as visible photocatalysts, in which porous g-C₃N₄ facilitated H₂ production from water splitting while the In₂O₃ nanosheets embedded in g-C₃N₄ pores favored CO₂ fixation and H adsorption onto the Lewis acid sites. Besides, the In₂O₃/g-C₃N₄ heterojunctions could efficiently inhibit the photoelectron–hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H₂ production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron–hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO₂ molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO₂ conversion was 63.1 μmol g⁻¹ h⁻¹ and could reach up to 736.3 μmol g⁻¹ h⁻¹ at 40 atm.

A multifunctional Pt/In₂O₃/g-C₃N₄ catalyst exhibited high activity and selectivity to HCOOH during CO₂ reduction owing to the synergy between visible-light harvesting, CO₂ activation, HER, and photoelectron–hole separation via heterojunctions.

Transition metal-based catalysts for the electrochemical CO2 reduction: from atoms and molecules to nanostructured materials

An overview of the main strategies for the rational design of transition metal-based catalysts for the electrochemical conversion of CO₂, ranging from molecular systems to single-atom and nanostructured catalysts.