Indium Cyanamide for Industrial-Grade CO2 Electroreduction to Formic Acid

Ligand-Driven Annular-Epitaxial Growth of CuS-Au Heterostructures as Trinity Plasmonic Nanozyme for Multimode Diagnosis of Pathogenic Bacteria

This study presents a novel method to control the site-selective growth of Au nanostars on CuS nanodisc substrate, it indicates that the surfactant ligands play a key role in the architecture control, only CTAC and homologous series with appropriate affinity to CuS can direct the annular-epitaxial growth of Au nanoparticles on the CuS, which demonstrates superior peroxidase (POD)-mimic and SERS activity. Mechanistic studies indicate that plasmon-enhanced catalytic and SERS activity can be attributed to the spatially separated CuS-Au heterostructure, which supports the light-triggered hot electron-hole pairs production and localized surface plasmon resonance hotspots. For practical biosensing, the CuS-Au heterostructures assembled lateral flow assay (LFA) was used for SERS/catalytic colorimetric/photothermal three-mode detection of Streptococcus pneumoniae and Klebsiella pneumoniae, with visually colorimetric mode at 103 CFU/mL and quantitative SERS/photothermal modes at 2-102 CFU/mL within 15 min, 15 clinical samples were used to validate the assay, the result was 100% concordant to the results of quantitative real-time PCR. This study provides a unique avenue to controllably produce plasmon-enhanced nanozyme, which can provide multi-mode signals for LFA application and meet the requirements of different scenarios.

Cerium Dioxide-Induced Abundant Cu+/Cu0 Sites for Electrocatalytic Reduction of Carbon Dioxide to C2+ Products

In recent years, the electrochemical reduction of carbon dioxide (CO2RR) has made many advances in C2+ production. Cu+/Cu0 site is beneficial for C-C coupling process, but the oxidation state of copper cannot be well maintained during the reaction process, resulting in a decrease in catalyst activity. Based on this consideration, in this work, transition metal oxide CeO2 with a hollow cube structure and oxygen vacancies was introduced to stabilize and increase Cu+/Cu0 active sites (Ce1Cu2). The catalyst exhibits excellent CO2RR performance, with FEC2+ achieving 73.52 % and jC2+ >280 mA/cm2 at 1.26 V (vs. RHE). Ethanol is the main C2+ product and FEethanol reaches 39 % at 1.26 V. The experimental results indicate that the presence of CeO2 provides a large number of oxygen vacancies and forming Cu+-O2--Ce4+ structure by the strong interaction of CeO2 and Cu NPs. The structure of Cu+-O2--Ce4+ and abundant oxygen vacancies lay a good foundation for the CO2 adsorption. Moreover, it increases the content of Cu+/Cu0 sites, effectively inhibiting hydrogen evolution reaction, promoting the C-C coupling interaction, thereby facilitating the generation of C2+ products. The DFT theoretical calculation further demonstrates that Ce1Cu2 is more inclined towards the ethanol pathway, confirming its high selectivity for ethanol.

Stabilizing Lattice Oxygen of Bi2O3 by Interstitial Insertion of Indium for Efficient Formic Acid Electrosynthesis

Bismuth oxide (Bi2O3) emerges as a potent catalyst for converting CO2 to formic acid (HCOOH), leveraging its abundant lattice oxygen and the high activity of its Bi-O bonds. Yet, its durability is usually impeded by the loss of lattice oxygen causing structure alteration and destabilized active bonds. Herein, we report an innovative approach via the interstitial incorporation of indium (In) into the Bi2O3, significantly enhancing bond stability and preserving lattice oxygen. The optimized In-Bi2O3-100 catalyst achieves over 90 % Faradaic efficiency for HCOOH production across a wide potential range, in both H-cells and flow cells, maintaining robust stability after 100 hours of continuous operation. In situ surface-enhanced infrared absorption spectroscopy and theoretical calculations reveal that the interstitial In doping precisely tunes the adsorption of CO2* and OCHO* intermediate, facilitating rapid conversion. Further in situ Raman spectroscopy confirms the role of In bolstering the oxidized structure's stability within Bi2O3, critical for sustaining lattice oxygen during electrochemical CO2 reduction.

A Copper-Zinc Cyanamide Solid-Solution Catalyst with Tailored Surface Electrostatic Potentials Promotes Asymmetric N-Intermediate Adsorption in Nitrite Electroreduction

The electrocatalytic nitrite reduction (NO2RR) converts nitrogen-containing pollutants to high-value ammonia (NH3) under ambient conditions. However, its multiple intermediates and multielectron coupled proton transfer process lead to low activity and NH3 selectivity for the existing electrocatalysts. Herein, we synthesize a solid-solution copper-zinc cyanamide (Cu0.8Zn0.2NCN) with localized structure distortion and tailored surface electrostatic potential, allowing for the asymmetric binding of NO2-. It exhibits outstanding NO2RR performance with a Faradaic efficiency of ∼100% and an NH3 yield of 22 mg h-1 cm-2, among the best for such a process. Theoretical calculations and in situ spectroscopic measurements demonstrate that Cu-Zn sites coordinated with linear polarized [NCN]2- could transform symmetric [Cu-O-N-O-Cu] in CuNCN-NO2- to a [Cu-N-O-Zn] asymmetric configuration in Cu0.8Zn0.2NCN-NO2-, thus enhancing adsorption and bond cleavage. A paired electro-refinery with the Cu0.8Zn0.2NCN cathode reaches 2000 mA cm-2 at 2.36 V and remains fully operational at industrial-level 400 mA cm-2 for >140 h with a NH3 production rate of ∼30 mgNH3 h-1 cm-2. Our work opens a new avenue of tailoring surface electrostatic potentials using a solid-solution strategy for advanced electrocatalysis.

Construction of an Indium-Based Coordination Polymer with Redox Non-Innocent Ligand for High-Efficient Electrochemical CO2 Reduction

Developing high-activity and long-term stable electrocatalysts for electrochemical CO2 reduction reaction (eCO2RR) to valuable products is still a challenge. An in-depth understanding of reaction mechanisms and the structure-function relationship is required for the development of an advanced catalytic eCO2RR system. Herein, a coordination polymer of indium(III) and benzenehexathiol (BHT) was developed as an electrocatalyst (In-BHT) for eCO2RR to HCOO-, which displayed an outstanding catalytic performance over the entire pH range. However, experimental results revealed significantly different catalytic pathways in the acid and neutral/alkaline solutions, which are attributed to the influence of redox non-innocent ligands on the rate-determining step (RDS). In the acid solution, the RDS is the formation of *OCOH intermediate through the proton transfer that originates from H2O in the solution, leading to relatively sluggish kinetics. But in the neutral or alkaline solution, the thiolate groups could be protonated during the catalytic process, and such proton can attack on carbon of absorbed CO2 via an intramolecular proton transfer, promoting the formation of *OCHO intermediate, resulting in faster kinetics. Our findings revealed the pivotal roles of the redox non-innocent ligands of metal active sites for eCO2RR, providing a new idea for designing highly efficient electrocatalysts.

Solar energy powered electrochemical reduction of CO2 on In2O3 nanosheets with high energy conversion efficiency at a large current density

Electrochemical CO2 reduction (ECO2R) to value-added chemicals offers a promising approach to both mitigate CO2 emission and facilitate renewable energy conversion. We demonstrate a solar energy powered ECO2R system operating at a relatively large current density (57 mA cm-2) using In2O3 nanosheets (NSs) as the cathode and a commercial perovskite solar cell as the electricity generator, which achieves the high solar to formate energy conversion efficiency of 6.6 %. The significantly enhanced operative current density with a fair solar energy conversion efficiency on In2O3 NSs can be ascribed to their high activity and selectivity for formate production, as well as the fast kinetics for ECO2R. The Faradic efficiencies (FEs) of formate In2O3 NSs are all above 93 %, with the partial current density of formate ranging from 2.3 to 342 mA cm-2 in a gas diffusion flow cell, which is among the widest for formate production on In-based catalysts. In-situ Raman spectroscopy and density functional theory simulations reveal that the exceptional performances of formate production on In2O3 NSs originates from the presence of abundant low coordinated edge sites, which effectively promote the selective adsorption of *OCHO while inhibiting *H adsorption.

Controllable Regulation of CO2 Adsorption Behavior via Precise Charge Donation Modulation for Highly Selective CO2 Electroreduction to Formic Acid

The synthesis of value-added products via CO2 electroreduction (CO2ER) is of great significance, but the development of efficient and versatile strategies for the controllable selectivity tuning is extremely challenging. Herein, the tuning of CO2ER selectivity through the modulation of CO2 adsorption behavior is proposed. Using the constructed zeolitic MOF (SNNU-339), CO2 adsorption behavior is controllably changed from *CO2 to CO2* via the precise ligand-to-metal charge donation (LTMCD) regulation. It is confirmed that the high electronegativity of the coordinate ligand directly restricts the LTMCD, reduces the charge density on the metal sites, lowers the Gibbs free energy for CO2* adsorption, and leads to the transformation of CO2 adsorption mode from *CO2 to CO2*. Owing to the modulated CO2 adsorption behavior and regulated kinetics, SNNU-339 exhibits superior HCOOH selectivity (≈330% promotion, 85.6% Faradaic efficiency) and high CO2ER activity. The wide applicability of the proposed approach sheds light on the efficient CO2ER. This study provides a competitive strategy for rational catalyst design and underscores the significance of adsorption behavior tuning in electrocatalysis.

Tailoring vinegar residue-derived all-carbon electrodes for efficient electrocatalytic carbon dioxide reduction to formate through heteroatom doping and defect enrichment

Electrocatalytic carbon dioxide reduction (ECO2R) to formate is the most technically and economically feasible approach to achieve electrochemical CO2 value addition. Here, a few-layer graphene is prepared from vinegar residue. Then a series of heteroatom-doped vertical graphene electrodes (X-rGO, X=P/S/N/B/, NS/NP/NB, NSP/NSB/NPB/NSPB) are prepared. The NS-rGO has improved ECO2R to formate selectivity (Faraday Efficiency (FEHCOO-) = 78.7 %) thanks to the synergistic effect between N and S. Carbon quantum dots (CQDs) are introduced into the electrode, the doped heteroatoms are further removed by high-temperature to form the defects-rich electrode (NS-CQDs-rGO-1100), which has better catalytic performance (FEHCOO-=90 %, stability over 10 h) with electrochemical double layer capacitance of 12.5 mF cm-2. The intrinsic effect of heteroatom doping and defects on the ECO2R activity of the electrodes are explored by density functional theory calculation. This work broadens the field of preparation of graphene and opens the door to the development of cost-effective electrocatalysts for efficient ECO2R.

Delocalization State-Stabilized Znδ+ Active Sites for Highly Selective and Durable CO2 Electroreduction

Zinc (Zn)-based materials are cost-effective and promising single-metal catalysts for CO2 electroreduction to CO but is still challenged by low selectivity and long-term stability. Undercoordinated Zn (Znδ+) sites have been demonstrated to be powerful active centers with appropriate *COOH affinity for efficient CO production However, electrochemical reduction conditions generally cause the inevitable reduction of Znδ+, resulting in the decline of CO efficiency over prolonged operation. Herein, a Zn cyanamide (ZnNCN) catalyst is constructed for highly selective and durable CO2 electroreduction, wherein the delocalized Zn d-electrons and resonant structure of cyanamide ligand prevent the self-reduction of ZnNCN and maintain Znδ+ sites under cathodic conditions. The mechanism studies based on density functional theory and operando spectroscopies indicate that delocalized Znδ+ site can stabilize the key *COOH intermediate through hard-soft acid-base theory, therefore thermodynamically promoting CO2-to-CO conversion. Consequently, ZnNCN delivers a CO Faradaic efficiency (FE) of up to 93.9% and further exhibits a remarkable stability lifespan of 96 h, representing a significant advancement in developing robust Zn-based electrocatalysts. Beyond expanding the variety of CO2 reduction catalysts, this work also offers insights into understanding the structure-function sensitivity and controlling dynamic active sites.

Diarylformamides as a Safe Reservoir and Room Temperature Source of Ultra-Pure CO in the Context of a 'Green' rWGS Reaction

Diphenylformamide 1 and bisformamide 9 are shown to be safe reservoirs and sources of CO. Their perfectly selective decarbonylations are achieved in solution at room temperature with potassium and cesium diarylamide catalysts. 1 is obtained in excellent yields directly from triethylammonium formate, which may be the product of CO2 scrubbing with NEt3 and catalytic hydrogenation. 1 thus represents a key intermediate in a low-temperature rWGS reaction sequence. Moreover, solvent-free decarbonylations of 1 may be run either in the melt at 70 °C or with 9 even in the solid state at 88 °C with improved atom economy. These simple and practical transition-metal-free decarbonylations afford ultra-pure (i. e. dry and solvent-free) CO at moderate temperatures and the diarylamines byproducts are recycled as pure compounds. In the absence of catalysts, diarylformamides 1 and 9 are long-term stable at >200 °C. DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph2NC(O)H and barrier-free CO elimination from Ph2NC(O)-.

Direct parallel electrosynthesis of high-value chemicals from atmospheric components on symmetry-breaking indium sites

To tackle significant environmental and energy challenges from increased greenhouse gas emissions in the atmosphere, we propose a method that synergistically combines cost-efficient integrated systems with parallel catalysis to produce high-value chemicals from CO2, NO, and other gases. We employed asymmetrically stretched InO5S with symmetry-breaking indium sites as a highly efficient trifunctional catalysts for NO reduction, CO2 reduction, and O2 reduction. Mechanistic studies reveal that the symmetry-breaking at indium sites substantially improves d-band center interactions and adsorption of intermediates, thereby enhancing trifunctional catalytic activity. Employed in a flow electrolysis system, the catalyst achieves continuous and flexible production of NH3, HCOO-, and H2O2, maintaining over 90% Faradaic efficiency at industrial scales. Notably, the parallel electrolysis device reported in this study effectively produces high-value products like NH4COOH directly from greenhouse gases in pure water, offering an economically efficient solution for small molecule synthesis and unique insights for the sustainable conversion of inexhaustible gases into valuable products. Therefore, this work possesses considerable potential for future practical applications in sustainable industrial processes.

Electrolyte-Assisted Structure Reconstruction Optimization of Sn-Zn Hybrid Oxide Boosts the Electrochemical CO2-to-HCOO- Conversion

Electrolyte plays crucial roles in electrochemical CO2 reduction reaction (e-CO2RR), yet how it affects the e-CO2RR performance still being unclarified. In this work, it is reported that Sn-Zn hybrid oxide enables excellent CO2-to-HCOO- conversion in KHCO3 with a HCOO- Faraday efficiency ≈89%, a yield rate ≈0.58 mmol cm-2 h-1 and a stability up to ≈60 h at -0.93 V, which are higher than those in NaHCO3 and K2SO4. Systematical characterizations unveil that the surface reconstruction on Sn-Zn greatly depends on the electrolyte using: the Sn-SnO2/ZnO, the ZnO encapsulated Sn-SnO2/ZnO and the Sn-SnO2/Zn-ZnO are reconstructed on the surface by KHCO3, NaHCO3 and K2SO4, respectively. The improved CO2-to-HCOO- performance in KHCO3 is highly attributed to the reconstructed Sn-SnO2/ZnO, which can enhance the charge transportation, promote the CO2 adsorption and optimize the adsorption configuration, accumulate the protons by enhancing water adsorption/cleavage and limit the hydrogen evolution. The findings may provide insightful understanding on the relationship between electrolyte and surface reconstruction in e-CO2RR and guide the design of novel electrocatalyst for effective CO2 reduction.

Stabilized Cu0 -Cu1+ dual sites in a cyanamide framework for selective CO2 electroreduction to ethylene

Electrochemical reduction of carbon dioxide to produce high-value ethylene is often limited by poor selectivity and yield of multi-carbon products. To address this, we propose a cyanamide-coordinated isolated copper framework with both metallic copper (Cu0) and charged copper (Cu1+) sites as an efficient electrocatalyst for the reduction of carbon dioxide to ethylene. Our operando electrochemical characterizations and theoretical calculations reveal that copper atoms in the Cuδ+NCN complex enhance carbon dioxide activation by improving surface carbon monoxide adsorption, while delocalized electrons around copper sites facilitate carbon-carbon coupling by reducing the Gibbs free energy for *CHC formation. This leads to high selectivity for ethylene production. The Cuδ+NCN catalyst achieves 77.7% selectivity for carbon dioxide to ethylene conversion at a partial current density of 400 milliamperes per square centimeter and demonstrates long-term stability over 80 hours in membrane electrode assembly-based electrolysers. This study provides a strategic approach for designing catalysts for the electrosynthesis of value-added chemicals from carbon dioxide.

A Regenerable Bi-Based Catalyst for Efficient and Stable Electrochemical CO2 Reduction to Formate at Industrial Current Densities

Renewable electricity shows immense potential as a driving force for the carbon dioxide reduction reaction (CO2RR) in production of formate (HCOO-) at industrial current density, providing a promising path for value-added chemicals and chemical manufacturing. However, achieving high selectivity and stable production of HCOO- at industrial current density remains a challenge. Here, we present a robust Bi0.6Cu0.4 NSs catalyst capable of regenerating necessary catalytic core (Bi-O) through cyclic voltammetry (CV) treatment. Notably, at 260 mA cm-2, faradaic efficiency of HCOO- reaches an exceptional selectivity to 99.23 %, maintaining above 90 % even after 400 h, which is longest reaction time reported at the industrial current density. Furthermore, in stability test, the catalyst was constructed by CV reconstruction to achieve stable and efficient production of HCOO-. In 20 h reaction test, the catalyst has a rate of HCOO- production of 13.24 mmol m-2 s-1, a HCOO- concentration of 1.91 mol L-1, and an energy consumption of 129.80 kWh kmol-1. In situ Raman spectroscopy reveals the formation of Bi-O structure during the gradual transformation of catalyst from Bi0.6Cu0.4 NBs to Bi0.6Cu0.4 NSs. Theoretical studies highlight the pivotal role of Bi-O structure in modifying the adsorption behavior of reaction intermediates, which further reduces energy barrier for *OCHO conversion in CO2RR.

Energy-efficient CO(2) conversion to multicarbon products at high rates on CuGa bimetallic catalyst

Electrocatalytic CO2 reduction to multi-carbon products is a promising approach for achieving carbon-neutral economies. However, the energy efficiency of these processes remains low, particularly at high current densities. Herein, we demonstrate that the low energy efficiencies are, in part, sometimes significantly, attributed to the high concentration overpotential resulting from the instability (i.e., flooding) of catalyst-layer during electrolysis. To tackle this challenge, we develop copper/gallium bimetallic catalysts with reduced activation energies for the formation of multi-carbon products. Consequently, the reduced activation overpotential allows us to achieve practical-relevant current densities for CO2 reduction at low cathodic potentials, ensuring good stability of the catalyst-layer and thereby minimizing the undesired concentration overpotential. The optimized bimetallic catalyst achieves over 50% cathodic energy efficiency for multi-carbon production at a high current density of over 1.0 A cm - 2 . Furthermore, we achieve current densities exceeding 2.0 A cm - 2 in a zero-gap membrane-electrode-assembly reactor, with a full-cell energy efficiency surpassing 30%.

pH-Universal Electrocatalytic CO2 Reduction with Ampere-Level Current Density on Doping-Engineered Bismuth Sulfide

The practical application of the electrocatalytic CO2 reduction reaction (CO2RR) to form formic acid fuel is hindered by the limited activation of CO2 molecules and the lack of universal feasibility across different pH levels. Herein, we report a doping-engineered bismuth sulfide pre-catalyst (BiS-1) that S is partially retained after electrochemical reconstruction into metallic Bi for CO2RR to formate/formic acid with ultrahigh performance across a wide pH range. The best BiS-1 maintains a Faraday efficiency (FE) of ~95 % at 2000 mA cm-2 in a flow cell under neutral and alkaline solutions. Furthermore, the BiS-1 catalyst shows unprecedentedly high FE (~95 %) with current densities from 100 to 1300 mA cm-2 under acidic solutions. Notably, the current density can reach 700 mA cm-2 while maintaining a FE of above 90 % in a membrane electrode assembly electrolyzer and operate stably for 150 h at 200 mA cm-2. In situ spectra and density functional theory calculations reveals that the S doping modulates the electronic structure of Bi and effectively promotes the formation of the HCOO* intermediate for formate/formic acid generation. This work develops the efficient and stable electrocatalysts for sustainable formate/formic acid production.

CuO (111) Microcrystalline Evoked Indium-Organic Framework for Efficient Electroreduction of CO2 to Formate

Electrochemical reduction of carbon dioxide (CO2RR) to formate is economically beneficial but suffers from poor selectivity and high overpotential. Herein, enriched microcrystalline copper oxide is introduced on the surface of indium-based metal-organic frameworks. Benefiting from the CuO (111) microcrystalline shell and formed catalytic active In-Cu interfaces, the obtained MIL-68(In)/CuO heterostructure display excellent CO2RR to formate with a Faradaic efficiency (FE) as high as 89.7% at low potential of only -0.7 V vs. RHE in a flow cell. Significantly, the membrane electrode assembly (MEA) cell based on MIL-68(In)/CuO exhibit a remarkable current density of 640.3 mA cm-2 at 3.1 V and can be stably operated for 180 h at 2.7 V with a current density of 200 mA cm-2. The ex/in situ electrochemical investigations reveal that the introduction of CuO increases the formation rate of the carbon dioxide reduction intermediate *HCOO- and inhibits the competitive hydrogen evolution reaction. This work not only provides an in-depth study of the mechanism of the CO2RR pathways on In/Cu composite catalyst but also offers an effective strategy for the interface design of electrocatalytic carbon dioxide reduction reaction.

Stabilizing the oxidation state of catalysts for effective electrochemical carbon dioxide conversion

In the electrocatalytic CO2 reduction reaction (CO2RR), metal catalysts with an oxidation state generally demonstrate more favorable catalytic activity and selectivity than their corresponding metallic counterparts. However, the persistence of oxidative metal sites under reductive potentials is challenging since the transition to metallic states inevitably leads to catalytic degradation. Herein, a thorough review of research on oxidation-state stabilization in the CO2RR is presented, starting from fundamental concepts and highlighting the importance of oxidation state stabilization while revealing the relevance of dynamic oxidation states in product distribution. Subsequently, the functional mechanisms of various oxidation-state protection strategies are explained in detail, and in situ detection techniques are discussed. Finally, the prevailing and prospective challenges associated with oxidation-state protection research are discussed, identifying innovative opportunities for mechanistic insights, technology upgrades, and industrial platforms to enable the commercialization of the CO2RR.

Efficient Capture and Electroreduction of Dilute CO2 into Highly Pure and Concentrated Formic Acid Aqueous Solution

High-purity CO2 rather than dilute CO2 (15 vol %, CO2/N2/O2 = 15:80:5, v/v/v) similar to the flue gas is currently used as the feedstock for the electroreduction of CO2, and the liquid products are usually mixed up with the cathode electrolyte, resulting in high product separation costs. In this work, we showed that a microporous conductive Bi-based metal-organic framework (Bi-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) can not only efficiently capture CO2 from the dilute CO2 under high humidity but also catalyze the electroreduction of the adsorbed CO2 into formic acid with a high current density of 80 mA cm-2 and a Faradaic efficiency of 90% at a very low cell voltage of 2.6 V. Importantly, the performance in a dilute CO2 atmosphere was close to that under a high-purity CO2 atmosphere. This is the first catalyst that can maintain exceptional eCO2RR performance in the presence of both O2 and N2. Moreover, by using dilute CO2 as the feedstock, a 1 cm-2 working electrode coating with Bi-HHTP can continuously produce a 200 mM formic acid aqueous solution with a relative purity of 100% for at least 30 h in a membrane electrode assembly (MEA) electrolyzer. The product does not contain electrolytes, and such a highly concentrated and pure formic acid aqueous solution can be directly used as an electrolyte for formic acid fuel cells. Comprehensive studies revealed that such a high performance might be ascribed to the CO2 capture ability of the micropores on Bi-HHTP and the lower Gibbs free energy of formation of the key intermediate *OCHO on the open Bi sites.

Concentrated Formic Acid from CO2 Electrolysis for Directly Driving Fuel Cell

The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial-level current densities (i.e., 200 mA cm-2 ) for 300 h on membrane electrode assembly using scalable lattice-distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2 % and a highest partial formate current density of 1.16 A cm-2 , reaching a production rate of 21.7 mmol cm-2  h-1 . To assess the practicality of this system, we perform a comprehensive techno-economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air-breathing formic acid fuel cells, boasting a power density of 55 mW cm-2 and an exceptional thermal efficiency of 20.1 %.

Recent research progresses of Sn/Bi/In-based electrocatalysts for electroreduction CO2 to formate

Carbon dioxide electroreduction reaction (CO2RR) can take full advantage of sustainable power to reduce the continuously increasing carbon emissions. Recycling CO2 to produce formic acid or formate is a technologically and economically viable route to accomplish CO2 cyclic utilization. Developing efficient and cost-effective electrocatalysts with high selectivity towards formate is prioritized for the industrialized applications of CO2RR electrolysis. From the previous explored CO2RR catalysts, Sn, Bi and In based materials have drawn increasing attentions due to the high selectivity towards formate. However, there are still confronted with several challenges for the practical applications of these materials. Therefore, a rational design of the catalysts for formate is urgently needed for the target of industrialized applications. Herein, we comprehensively summarized the recent development in the advanced electrocatalysts for the CO2RR to formate. Firstly, the reaction mechanism of CO2RR is introduced. Then the preparation and design strategies of the highly active electrocatalysts are presented. Especially the innovative design mechanism in engineering materials for promoting catalytic performance, and the efforts on mechanistic exploration using in situ (ex situ) characterization techniques are reviewed. Subsequently, some perspectives and expectations are proposed about current challenges and future potentials in CO2RR research.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Active-site stabilized Bi metal-organic framework-based catalyst for highly active and selective electroreduction of CO2 to formate over a wide potential window

Bismuth-based materials have been validated to be a kind of effective electrocatalyst for electrocatalytic CO2 reduction (ECR) to formate (HCOO-). However, the established studies still encounter the problems of low current density, low selectivity, narrow potential window, and poor catalyst stability. Herein, a bismuth-terephthalate framework (Bi-BDC MOF) material was successfully synthesized. The optimized Bi-BDC-120 °C exhibited excellent activity, selectivity, and durability for formate production. At an operating potential of -1.1 V vs. RHE in 0.1 mol L-1 KHCO3 electrolyte, the ECR catalyzed by Bi-BDC-120 °C achieved a Faraday efficiency (FE) of 97.2% towards formate generation, and the total current density reached about 30 mA cm-2. The operating potential window with FEformate values > 95% ranged in -0.9 to -1.5 V vs. RHE. The density-functional theory (DFT) calculation demonstrated that the (001) crystalline planes of Bi-BDC are preferable for the adsorption of CO2 and the conversion of *OCHO intermediates, thus ultimately promoting the electrocatalytic production of formate. Although the MOF structure of Bi-BDC-120 °C was insufficiently stabilized, the FEformate could be maintained at around 90% after 36 h of ECR operation. The long-term durability for formate production was attributed to the fact that the in situ reconstructed Bi2O2CO3 could retain the Bi-O active sites in the structure. These results offer an opportunity to design CO2 reduction electrocatalysts with high activity and selectivity for potential applications.

Restraining Interfacial Cu2+ by using Amorphous SnO2 as Sacrificial Protection Boosts CO2 Electroreduction

The electrochemical carbon dioxide reduction reaction (CO2 RR) to formate is of great interest in the field of electrochemical energy. Cu-based material is an appealing electrocatalyst for the CO2 RR. However, retaining Cu2+ under the high cathodic potential of CO2 RR remains a great challenge, leading to low electrocatalytic selectivity, activity, and stability. Herein, inspired by corrosion science, a sacrificial protection strategy to stabilize interfacial crystalline CuO through embedding of active amorphous SnO2 (c-CuO/a-SnO2 ) is reported, which greatly boosts the electrocatalytic sensitivity, activity, and stability for CO2 RR to formate. The as-made hybrid catalyst can achieve superior high selectivity for CO2 RR to formate with a remarkable Faradaic efficiency (FE) of 96.7%, and a superhigh current density of over 1 A cm-2 that far outperforms industrial benchmarks (FE > 90%, current density > 300 mA cm-2 ). In situ X-ray absorption spectroscopy (XAS) and X-ray diffractionexperimental and theoretical calculation results reveal that the broadened s-orbital in interfacial a-SnO2 offers the lower orbital for extra electrons than Cu2+ , which can effectively retain nearby Cu2+ , and the high active interface significantly lowers the energy barrier of the limited step (* CO2 → * HCOO) and enhances the selectivity and activity for CO2 RR to formate.