Turning Waste into Wealth: Sustainable Production of High-Value-Added Chemicals from Catalytic Coupling of Carbon Dioxide and Nitrogenous Small Molecules

Carbon neutrality is one of the central topics of not only the scientific community but also the majority of human society. The development of highly efficient carbon dioxide (CO₂) capture and utilization (CCU) techniques is expected to stimulate routes and concepts to go beyond fossil fuels and provide more economic benefits for a carbon-neutral economy. While various single-carbon (C₁) and multi-carbon (C₂₊) products have been selectively produced to date, the scope of CCU can be further expanded to more valuable chemicals beyond simple carbon species by integration of nitrogenous reactants into CO₂ reduction. In this Review, research progress toward sustainable production of high-value-added chemicals (urea, methylamine, ethylamine, formamide, acetamide, and glycine) from catalytic coupling of CO₂ and nitrogenous small molecules (NH₃, N₂, NO₃^-, and NO₂^-) is highlighted. C-N bond formation is a key mechanistic step in N-integrated CO₂ reduction, so we focus on the possible pathways of C-N coupling starting from the CO₂ reduction and nitrogenous small molecules reduction processes as well as the catalytic attributes that enable the C-N coupling. We also propose research directions and prospects in the field, aiming to inspire future investigations and achieve comprehensive improvement of the performance and product scope of C-N coupling systems.

Bridge Sites of Au Surfaces Are Active for Electrocatalytic CO2 Reduction

Prior in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) studies of electrochemical CO2 reduction catalyzed by Au, one of the most selective and active electrocatalysts to produce CO from CO2, suggest that the reaction proceeds solely on the top sites of the Au surface. This finding is worth updating with an improved spectroelectrochemical system where in situ IR measurements can be performed under real reaction conditions that yield high CO selectivity. Herein, we report the preparation of an Au-coated Si ATR crystal electrode with both high catalytic activity for CO2 reduction and strong surface enhancement of IR signals validated in the same spectroelectrochemical cell, which allows us to probe the adsorption and desorption behavior of bridge-bonded *CO species (*COB). We find that the Au surface restructures irreversibly to give an increased number of bridge sites for CO adsorption within the initial tens of seconds of CO2 reduction. By studying the potential-dependent desorption kinetics of *COB and quantifying the steady-state surface concentration of *COB under reaction conditions, we further show that *COB are active reaction intermediates for CO2 reduction to CO on this Au electrode. At medium overpotential, as high as 38% of the reaction occurs on the bridge sites.

Construction of the Sn-doped defect pyrochlore oxide KNbMoO6·H2O/g-C3N4 composite and its photocatalytic reduction of CO2

The Sn-doped defect pyrochlore oxide KNbMoO6·H2O/g-C3N4 composite can be used as a photocatalyst for conversion of CO2 in order to deal with energy and environmental issues.

Accessing Organonitrogen Compounds via C-N Coupling in Electrocatalytic CO2 Reduction

Given the limited product variety of electrocatalytic CO₂ reduction reactions solely from CO₂ and H₂O as the reactants, it is desirable to expand the product scope by introducing additional reactants that provide elemental diversity. The integration of inorganic heteroatom-containing reactants into electrocatalytic CO₂ reduction could, in principle, enable the sustainable synthesis of valuable products, such as organonitrogen compounds, which have widespread applications but typically rely on NH₃ derived from the energy-intensive and fossil-fuel-dependent Haber-Bosch process for their industrial-scale production. In this Perspective, research progress toward building C-N bonds in N-integrated electrocatalytic CO₂ reduction is highlighted, and the electrosyntheses of urea, acetamides, and amines are examined from the standpoints of reactivity, catalyst structure, and, most fundamentally, mechanism. Mechanistic discussions of C-N coupling in these advances are emphasized and critically evaluated, with the aim of directing future investigations on improving the product yield and broadening the product scope of N-integrated electrocatalytic CO₂ reduction.

Recent Advances in Interface Engineering for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO₂ reduction reaction (CO₂RR) can store and transform the intermittent renewable energy in the form of chemical energy for industrial production of chemicals and fuels, which can dramatically reduce CO₂ emission and contribute to carbon-neutral cycle. Efficient electrocatalytic reduction of chemically inert CO₂ is challenging from thermodynamic and kinetic points of view. Therefore, low-cost, highly efficient, and readily available electrocatalysts have been the focus for promoting the conversion of CO₂. Very recently, interface engineering has been considered as a highly effective strategy to modulate the electrocatalytic performance through electronic and/or structural modulation, regulations of electron/proton/mass/intermediates, and the control of local reactant concentration, thereby achieving desirable reaction pathway, inhibiting competing hydrogen generation, breaking binding-energy scaling relations of intermediates, and promoting CO₂ mass transfer. In this review, we aim to provide a comprehensive overview of current developments in interface engineering for CO₂RR from both a theoretical and experimental standpoint, involving interfaces between metal and metal, metal and metal oxide, metal and nonmetal, metal oxide and metal oxide, organic molecules and inorganic materials, electrode and electrolyte, molecular catalysts and electrode, etc. Finally, the opportunities and challenges of interface engineering for CO₂RR are proposed.

Boosting carbon monoxide production during CO2 reduction reaction via Cu-Sb2O3 interface cooperation

Development of multiple-component catalyst materials is a new trend in electrochemical CO₂ reduction reaction (eCO₂RR). A new type of metal-oxide interaction is reported here to improve carbon monoxide production via synergistic effect between the CO₂-to hydrocarbon selective metal material and CO₂-to hydrogen generation oxide material. Cu/Sb₂O₃ material originates from the hetero-structured CuO/Sb₂O₃ by a facile two-step hydrolysis and precipitation method, cooperative to inhibit hydrogen evolution or methane product, achieving CO Faradaic efficiency to 92% in CO₂ saturated KCl electrolyte at -0.99 V with good stability. The formation of a stable *COOH intermediate by electronic and geometric effects via Cu and Sb₂O₃ are responsible to promote CO selectivity. Cu-Sb₂O₃ interface interaction also destabilizes the adsorption *H as well, an intermediate for H₂ evolution. This study proposes a versatile design strategy for construction and utilization of metal-oxide interface for eCO₂RR.

Optimization Strategies for Selective CO2 Electroreduction to Fuels

Capturing CO2 from the atmosphere and converting it into fuels are an efficient strategy to stop the deteriorating greenhouse effect and alleviate the energy crisis. Among various CO2 conversion approaches, electrocatalytic CO2 reduction reaction (CO2RR) has received extensive attention because of its mild operating conditions. However, the high onset potential, low selectivity toward multi-carbon products and poor cruising ability of CO2RR impede its development. To regulate product distribution, previous studies performed electrocatalyst modification using several universal methods, including composition manipulation, morphology control, surface modification, and defect engineering. Recent studies have revealed that the cathode and electrolytes influence the selectivity of CO2RR via pH changes and ionic effects, or by directly participating in the reduction pathway as cocatalysts. This review summarizes the state-of-the-art optimization strategies to efficiently enhance CO2RR selectivity from two main aspects, namely the cathode electrocatalyst and the electrolyte.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Interface Engineering of Silver-Based Heterostructures for CO2 Reduction Reaction

The production of CO from the CO₂ reduction reaction (CO₂RR) is of great interest in the renewable energy storage and conversion, the neutral carbon emission, and carbon recycle utilization. Silver (Ag) is one of the catalytic metals that are active for electrochemical CO₂ reduction into CO, but the catalysis requires a large overpotential to achieve higher selectivity. Constructing a metal-oxide interface could be an effective strategy to boost both activity and selectivity of the catalysis. Herein, density functional theory (DFT) calculations were first conducted to reveal the chemical insights of the catalytic performance on the interface between metal oxide and Ag(111) (MO_x/Ag(111)). The results show that the *COOH intermediates can be more stabilized on the surfaces of MO_x/Ag(111) than pure Ag(111). The hydrogen evolution reaction on MO_x/Ag(111) can be suppressed due to the significantly higher Gibbs free energy for hydrogen adsorption (ΔG_H*), thereby enhancing the selectivity toward CO₂RR. A series of MO_x/Ag composites with the unique interface based on the DFT results were then introduced though a two-step approach. The as-obtained MO_x/Ag catalysts boosted both the CO activity and selectivity at a relatively positive potential range, especially in the case of MnO₂/Ag. The reduction current density on the MnO₂/Ag catalyst can reach 4.3 mA cm^-2 at -0.7 V (vs RHE), which is 21.5 times higher than that on pure Ag, and the overpotential of CO₂ to CO (390 mV) possesses is much lower than that on pure Ag NPs (690 mV). This study proposes an effective design strategy to construct a metal-oxide interface for CO₂RR based on the synergistic effect between metals and MO_x.

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.

Decoration of In nanoparticles on In2S3 nanosheets enables efficient electrochemical reduction of CO2

Decorating the In₂S₃ nanosheets with in situ formed In nanoparticles boosted the CO₂ electroreduction.

The role of adsorbed oleylamine on gold catalysts during synthesis for highly selective electrocatalytic reduction of CO2 to CO

Adsorbed oleylamine on Au NP surfaces during preparation can efficiently enhance electrocatalysis of CO₂ to CO and inhibit the hydrogen evolution reaction.