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A Cu2O-derived catalyst selectively and durably electroreduces CO2 to formate with a maximum faradaic efficiency of 74% in S2−-containing electrolyte and exhibits a high formate partial current density of up to 110 mA cm−2 in a flow cell. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction to value‐added chemicals or fuels offers a promising approach to reduce carbon emissions and alleviate energy shortage. Cu‐based electrocatalysts have been widely reported as capable of reducing CO2 to produce a variety of multicarbon products (e.g. ethylene and ethanol). In this work, we develop sulfur‐doped Cu2O electrocatalysts, which instead can electrochemically reduce CO2 to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu2O‐electrolyte interface, and S‐doped Cu2O undergoes in situ surface reconstruction to generate active S‐adsorbed metallic Cu sites during the CO2 reduction reaction (CO2RR). Density functional theory (DFT) calculations together with in situ infrared absorption spectroscopy measurements show that the S‐adsorbed metallic Cu surface can not only promote the formation of the *OCHO intermediate but also greatly suppress *H and *COOH adsorption, thus facilitating CO2‐to‐formate conversion during the electrochemical CO2RR. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction to value‐added chemicals/fuels provides a promising way to mitigate CO2 emission and alleviate energy shortage. CO2‐to‐CO conversion involves only two‐electron/proton transfer and thus is kinetically fast. Among the various developed CO2‐to‐CO reduction electrocatalysts, transition metal/N‐doped carbon (M‐N‐C) catalysts are attractive due to their low cost and high activity. In this work, recent progress on the development of M‐N‐C catalysts for electrochemical CO2‐to‐CO conversion is reviewed in detail. The regulation of the active sites in M‐N‐C catalysts and their related adjustable electrocatalytic CO2 reduction performance is discussed. A visual performance comparison of M‐N‐C catalysts for CO2 reduction reaction (CO2RR) reported over the recent years is given, which suggests that Ni and Fe‐N‐C catalysts are the most promising candidates for large‐scale reduction of CO2 to produce CO. Finally, outlooks and challenges are proposed for future research of CO2‐to‐CO conversion. [ABSTRACT FROM AUTHOR]

It is widely accepted that single Ni atoms coordinated with N can highly efficiently promote CO2 electroreduction to CO. Very recently, probably due to limited access to high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) techniques, a misleading conclusion that nitrogen‐doped carbon‐encapsulated Ni nanoparticles (NPs) possess activity similar to that of single Ni atoms was reported and was quickly followed by several similar reports. The current contribution aims to end this misleading conclusion by performing well‐designed experiments and solid theoretical analyses. For this purpose, a series of Ni/nitrogen‐doped graphite (Ni‐NG) catalysts with different dominant Ni species (single Ni atom, nitrogen‐doped carbon‐encapsulated Ni NPs, or both) are fabricated and comparatively studied for CO2 electroreduction to CO. Two previous studies that reported nitrogen‐doped carbon‐encapsulated Ni NPs catalysts are reinvestigated, and the existence of single Ni atoms is confirmed by HAADF‐STEM. In addition, after leaching out most of the Ni NPs by a strong acid, the activity of those catalysts does not decrease but increases slightly. Density functional theory results suggest that nitrogen‐doped carbon‐encapsulated Ni NPs are highly selective for the hydrogen evolution reaction (HER) rather than for CO2‐to‐CO conversion. Overall, both systematic experimental and theoretical analyses clearly reveal that the nitrogen‐doped carbon‐encapsulated Ni NPs are not active for CO2 electroreduction. [ABSTRACT FROM AUTHOR]

• A critical review on the influence of reactor design for electrochemical CO 2 reduction. • The feature, advantage and disadvantage of all types of electrolytic cells are compared. • H-type cell, flow cell and DEMS cell are emphasized with good potentials. • Perspectives and challenges for electrochemical cells are discussed. Transmute CO 2 to value-added chemical products by electrochemical reduction is a potential candidate and a highly providential route to mitigate CO 2 levels in atmosphere and meet the energy and global warming crisis. Recent reported studies have focused on advancement of novel electro-catalysts with outstanding performance, but unfortunately, little attention has been paid to the influence of reactor design. In this contribution, we for the first time comprehensively review all types of electrolytic cells reported in literatures and compare their features, advantages and disadvantages for CO 2 electro-reduction. To date, H-type cell is still the well-known typical reactor for CO 2 RR, typically for screening electro-catalysts. Based on H-type cell, a similar modified sandwich-type cell is designed to reduce system resistance. However, for industrialization, the flow cell in which the reactants and products are continuously transferred to and away from the electrodes, need further advancement because of its efficient mass transfer efficiency. Besides, the DEMS cell is an effective way to detect products efficiently in real time and analyze reaction process, which is useful for seeking reaction mechanism. The perspectives and challenges for the development of electrochemical cells are also addressed. We hopeful, this review should provide researchers with a clearer understanding of reactor selection, and impart important, timely and valuable insights into the design of advance electrolytic cells and its practical applications for CO 2 reduction. [ABSTRACT FROM AUTHOR]

Increasing the amount of accessible active sites to reactants is an effective way to enhance electrocatalytic activity. Although single-atom catalysts are claimed to be capable of achieving 100% atomic utilization, there may be abundant single-atom sites buried and inaccessible to reactants in practice. Herein, two Ni, N-doped carbon catalysts with Ni-N x atomic sites are comparatively studied for CO 2 electroreduction. In contrast to the Ni-N x /Carbon nanosheets with Ni loading of 2.42 wt%, the Ni-N x /Carbon black with lower Ni loading of 0.16 wt% excitingly exhibits higher activity for CO production. The atomically dispersed Ni-Nx sites over carbon black surface benefit the exposure and utilization of single-atom sites, leading to a significant increase of TOF from 2140 to 100,347 h−1 at − 0.8 V. Particularly, an extraordinarily high current density up to 300 mA cm−2 with CO selectivity of ∼100 % are achieved for Ni-N x /CB in the flow cell. This work demonstrates the significance of increasing single-atom site utilization. [Display omitted] • Ni-Nx/CNS and Ni-Nx/CB catalysts with Ni-Nx sites are synthesized for CO2RR. • Ni-Nx/CB catalyst exhibits high CO selectivity and TOF for CO2 conversion. • Ni-Nx/CB catalyst with low Ni loading exhibits high single-Ni-atoms utilization. • High current density of > 300 mA cm-2 is achieved in the flow cell. [ABSTRACT FROM AUTHOR]

The membrane Electrode Assemblies (MEAs) electrolyzers are the most attractive systems for the electrolytic conversion of CO 2 into commodity chemicals and fuels at commercially relevant current densities. Suppressing the hydrogen evolution reaction (HER) is vital to the highly efficient electrochemical CO 2 reduction reaction (CO 2 RR). However, little attention has been paid to the HER. Herein, polybenzimidazole (PBI) Janus membranes with significant hydrophobic/hydrophilic asymmetric surface wettability were constructed for regulating the HER in CO 2 RR. The HER was modulated by adjusting the microstructure and surface hydrophobicity of the membrane as well as the CO 2 feeding method. The p-PBI-HCF MEA showed a significant suppression of HER and a 6-fold improvement in CO selectivity over p-PBI MEA. The p-PBI-HCF exhibited superior CO 2 RR performance in MEA compared to commercial membranes (FAA-3-50 and Nafion115). At 2.0–3.0 V, the CO Faraday efficiency (FE CO) of the p-PBI-HCF MEA electrolyzer remained above 92%. The optimal energy efficiency range was between 2.0 and 2.4 V when the FE CO was close to 100%. The p-PBI-HCF provided 92% FE CO and a current density of 225 mA cm−2 at 3 V. This work provides guidelines for the development of viable PBI membranes and MEAs for CO 2 RR. [Display omitted] • HER was regulated by microstructure and surface hydrophobicity as well as by the humidified or dry state of CO 2. • HER was significantly suppressed and the CO selectivity was improved by 6 times after the regulatory measures were applied. • Controlling the local microenvironment at the cathode is vital to avoid high HER. • The FE CO approached 100% at 2.0–2.4 V while demonstrating the best efficiency range. [ABSTRACT FROM AUTHOR]