The continuously increasing CO2 released from human activities poses a great threat to human survival by fluctuating global climate and disturbing carbon balance among the four reservoirs of the biosphere, earth, air, and water. Converting CO2 to value-added feedstocks via electrocatalysis of the CO2 reduction reaction (CO2RR) has been regarded as one of the most attractive routes to re-balance the carbon cycle, thanks to its multiple advantages of mild operating conditions, easy handling, tunable products and the potential of synergy with the rapidly increasing renewable energy (i.e., solar, wind). Instead of focusing on a special topic of electrocatalysts for the CO2RR that have been extensively reviewed elsewhere, we herein present a rather comprehensive review of the recent research progress, in the view of associated value-added products upon selective electrocatalytic CO2 conversion. We initially provide an overview of the history and the fundamental science regarding the electrocatalytic CO2RR, with a special introduction to the design, preparation, and performance evaluation of electrocatalysts, the factors influencing the CO2RR, and the associated theoretical calculations. Emphasis will then be given to the emerging trends of selective electrocatalytic conversion of CO2 into a variety of value-added products. The structure-performance relationship and mechanism will also be discussed and investigated. The outlooks for CO2 electrocatalysis, including the challenges and opportunities in the development of new electrocatalysts, electrolyzers, the recently rising operando fundamental studies, and the feasibility of industrial applications are finally summarized.

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

Catalytic conversion of CO2 to produce fuels and chemicals is attractive in prospect because it provides an alternative to fossil feedstocks and the benefit of converting and cycling the greenhouse gas CO2 on a large scale. In today's technology, CO2 is converted into hydrocarbon fuels in Fischer-Tropsch synthesis via the water gas shift reaction, but processes for direct conversion of CO2 to fuels and chemicals such as methane, methanol, and C2+ hydrocarbons or syngas are still far from large-scale applications because of processing challenges that may be best addressed by the discovery of improved catalysts-those with enhanced activity, selectivity, and stability. Core-shell structured catalysts are a relatively new class of nanomaterials that allow a controlled integration of the functions of complementary materials with optimised compositions and morphologies. For CO2 conversion, core-shell catalysts can provide distinctive advantages by addressing challenges such as catalyst sintering and activity loss in CO2 reforming processes, insufficient product selectivity in thermocatalytic CO2 hydrogenation, and low efficiency and selectivity in photocatalytic and electrocatalytic CO2 hydrogenation. In the preceding decade, substantial progress has been made in the synthesis, characterization, and evaluation of core-shell catalysts for such potential applications. Nonetheless, challenges remain in the discovery of inexpensive, robust, regenerable catalysts in this class. This review provides an in-depth assessment of these materials for the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2 into synthesis gas and valuable hydrocarbons.

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Core–shell structured catalysts for thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2

CO2 electrochemical reduction shows great promise in storing renewable energy and alleviating global warming. Its large-scale applications in the industry, however, are still in infancy mainly due to the unsatisfactory performance of electrocatalysts. Rational design of advanced electrocatalysts would be the ultimate solution, which has yet to be achieved currently because of the lack of understandings of reaction mechanisms. In the past few years, in situ attenuated total reflection infrared (ATR-IR) spectroscopy has been successfully adopted to study the electrochemical interface of the CO2 reduction reaction (CO2RR) and significantly advanced our understandings of this reaction. In this Perspective, these advances as well as the challenges and opportunities faced in further studying CO2RR by this technique are discussed.

CO2 Electrochemical Reduction As Probed through Infrared Spectroscopy

Alloying is an important strategy for the design of catalytic materials beyond pure metals. The conventional alloy catalysts however lack precise control over the local atomic structures of active ...

Ensemble Effect in Bimetallic Electrocatalysts for CO2 Reduction

Electrochemical reduction of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. However, the development of electrocatalysts with high activity and selectivity in a wide potential window is challenging. Herein, atomically thin bismuthene (Bi-ene) is pioneeringly obtained by an in situ electrochemical transformation from ultrathin bismuth-based metal-organic layers. The few-layer Bi-ene, which possesses a great mass of exposed active sites with high intrinsic activity, has a high selectivity (ca. 100 %), large partial current density, and quite good stability in a potential window exceeding 0.35 V toward formate production. It even deliver current densities that exceed 300.0 mA cm-2 without compromising selectivity in a flow-cell reactor. Using in situ ATR-IR spectra and DFT analysis, a reaction mechanism involving HCO3- for formate generation was unveiled, which brings new fundamental understanding of CO2 reduction.

Metal-Organic Layers Leading to Atomically Thin Bismuthene for Efficient Carbon Dioxide Electroreduction to Liquid Fuel.

Tuning Structural and Compositional Effects in Pd–Au Nanowires for Highly Selective and Active CO2 Electrochemical Reduction Reaction

Achieving a high faradaic efficiency and mass activity simultaneously on catalysts is critical in accelerating the practical application of CO2 electrochemical reduction. In this study, Au–Pd core–shell nanoparticles consisting of an ultrathin Pd-rich shell and an Au–Pd alloy core are developed by a simple one-pot synthesis method and evaluated for CO2-to-CO conversion. By adjusting the Au : Pd feeding ratio, the shell thickness and composition in the nanoparticle can be tuned. Significantly improved CO selectivity as compared to pure Au and Pd counterparts can be obtained on all the synthesized Au–Pd core–shell nanoparticles with a maximum faradaic efficiency of 96.7% at −0.6 V. The Au94Pd6 catalyst shows an ultrahigh mass activity of 99.8 A gPd+Au−1 for CO production at an overpotential of merely 390 mV. Combined in situ infrared absorption spectroscopy and density functional theory studies reveal that the easier desorption of *CO due to the more balanced *COOH/*CO adsorption energies on Au–Pd core–shell surfaces is responsible for the improved catalytic performance.

Composition-dependent CO2 electrochemical reduction activity and selectivity on Au–Pd core–shell nanoparticles

Fuel cell technology is a clean way of generating energy and should enable carbon neutrality. However, although traditional proton exchange membrane fuel cells (PEMFCs) have made a commercial impact, their high cost hinders their wider adoption. Fuel cells that use anion exchange membranes (AEMs) are a promising alternative to PEMFCs, as they can achieve the same performance at a lower cost. In this Perspective, recent trends in the fabrication of polymer‐based high‐performance AEMs are highlighted and future directions are identified. Since ensuring the durability of polymers in strong alkaline conditions is the most critical issue in the development of AEM fuel cells, strategies for the formation of polymers with chemical stability, mechanical stability, and ionic conductivity are primarily focused on. Successes in polymer design are expected to inaugurate the next generation of AEMs and trigger a fresh wave of innovation, leading to the development of long‐lasting fuel cells that reduce carbon emissions and facilitate sustainable development.

Anion Exchange Membranes for Fuel Cells: State‐of‐the‐Art and Perspectives

An enantioselective NiH-catalyzed hydroalkynylation of α,β -unsaturated amides is reported. A wide range of α,β -unsaturated amides and bromoalkynes are suitable substrates for this reaction, which proceeds under mild conditions, allowing access to a variety of enantioenriched chiral β -alkynyl amides. β,γ -Unsaturated amides can also be used as substrates and undergo the β -selective hydroalkynylation with a slightly lower enantiomeric excess. A regio-reversed and enantiodifferentiating syn -hydrometalation of α,β -unsaturated amides with nickel hydride, followed by a subsequent stereospecific cross-coupling with bromoalkynes, is a convenient approach to the synthesis of enantioenriched chiral β -alkynyl amides. 

Ran Tao

Papers

Tuning Structural and Compositional Effects in Pd–Au Nanowires for Highly Selective and Active CO2 Electrochemical Reduction Reaction

Composition-dependent CO2 electrochemical reduction activity and selectivity on Au–Pd core–shell nanoparticles

Anion Exchange Membranes for Fuel Cells: State‐of‐the‐Art and Perspectives

NiH-catalyzed asymmetric hydroalkynylation of α,β-unsaturated amides