High-Curvature Transition-Metal Chalcogenide Nanostructures with a Pronounced Proximity Effect Enable Fast and Selective CO2 Electroreduction

A considerable challenge in the conversion of carbon dioxide into useful fuels comes from the activation of CO₂ to CO₂^.− or other intermediates, which often requires precious-metal catalysts, high overpotentials, and/or electrolyte additives (e.g., ionic liquids). We report a microwave heating strategy for synthesizing a transition-metal chalcogenide nanostructure that efficiently catalyzes CO₂ electroreduction to carbon monoxide (CO). We found that the cadmium sulfide (CdS) nanoneedle arrays exhibit an unprecedented current density of 212 mA cm⁻² with 95.5±4.0 % CO Faraday efficiency at −1.2 V versus a reversible hydrogen electrode (RHE; without iR correction). Experimental and computational studies show that the high-curvature CdS nanostructured catalyst has a pronounced proximity effect which gives rise to large electric field enhancement, which can concentrate alkali-metal cations resulting in the enhanced CO₂ electroreduction efficiency.     

Engineering electronic structures of nanomaterials toward carbon dioxide electroreduction

The electroreduction of CO₂ into valuable products holds the prospect for the shortage of fossil fuels and global warming. For the design of catalysts, manipulating the electronic structures of catalysts plays a vital role in the adsorption, activation, and desorption behaviors during the catalytic process. Here, we summarize recent progress in CO₂ electroreduction from the perspective of engineering electronic structures of catalysts. The strategies include vacancy engineering, heteroatom substitution, atomic layer regulation, sharp-tip effect, and interlayer bond length regulation. Particularly, combining with the experimental and theoretical results reported previously, we provide an atomic-level insight into the effect of electronic structure on CO₂ activation.     

Metal‐Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons

This study explores the kinetics, mechanism, and active sites of the CO₂ electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon‐based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO₂ to CO/H₂ mixtures outperforming a low‐area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low‐cost, abundant electrocatalysts for synthetic fuel production from CO₂.     

High‐Curvature Transition‐Metal Chalcogenide Nanostructures with a Pronounced Proximity Effect Enable Fast and Selective CO2 Electroreduction

A considerable challenge in the conversion of carbon dioxide into useful fuels comes from the activation of CO₂ to CO₂^.? or other intermediates, which often requires precious‐metal catalysts, high overpotentials, and/or electrolyte additives (e.g., ionic liquids). We report a microwave heating strategy for synthesizing a transition‐metal chalcogenide nanostructure that efficiently catalyzes CO₂ electroreduction to carbon monoxide (CO). We found that the cadmium sulfide (CdS) nanoneedle arrays exhibit an unprecedented current density of 212 mA cm^?2 with 95.5±4.0 % CO Faraday efficiency at ?1.2 V versus a reversible hydrogen electrode (RHE; without iR correction). Experimental and computational studies show that the high‐curvature CdS nanostructured catalyst has a pronounced proximity effect which gives rise to large electric field enhancement, which can concentrate alkali‐metal cations resulting in the enhanced CO₂ electroreduction efficiency.     

Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol

The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO₂ as a possible feedstock. While CO₂ electroreduction (CO₂R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO₂R, a two-step process, with first CO₂R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step. Here we report a novel copper-based catalyst, silver-doped copper nitride, with record selectivity for formation of propanol (Faradaic efficiency: 45 %), an industrially relevant compound, from CO electroreduction in gas-fed flow cells. Selective propanol formation occurs at metallic copper atoms derived from copper nitride and is promoted by silver doping as shown experimentally and computationally. In addition, the selectivity for C₂₊ liquid products (Faradaic efficiency: 80 %) is among the highest reported so far. These findings open new perspectives regarding the design of catalysts for production of C₃ compounds from CO₂.     

Electrochemical Reduction of Carbon Dioxide to Methanol on Hierarchical Pd/SnO2 Nanosheets with Abundant Pd–O–Sn Interfaces

Electrochemical conversion of CO₂ into fuels using electricity generated from renewable sources helps to create an artificial carbon cycle. However, the low efficiency and poor stability hinder the practical use of most conventional electrocatalysts. In this work, a 2D hierarchical Pd/SnO₂ structure, ultrathin Pd nanosheets partially capped by SnO₂ nanoparticles, is designed to enable multi‐electron transfer for selective electroreduction of CO₂ into CH₃OH. Such a structure design not only enhances the adsorption of CO₂ on SnO₂, but also weakens the binding strength of CO on Pd due to the as‐built Pd–O–Sn interfaces, which is demonstrated to be critical to improve the electrocatalytic selectivity and stability of Pd catalysts. This work provides a new strategy to improve electrochemical performance of metal‐based catalysts by creating metal oxide interfaces for selective electroreduction of CO₂.     

Oxygenates from the Electrochemical Reduction of Carbon Dioxide

Electrochemical reduction of carbon dioxide (CO₂) driven by renewable electricity to give chemicals and fuels is considered an ideal approach that can alleviate both carbon emission and energy tension stress. High‐value chemicals such as oxygenates can be effectively produced from the electroreduction of CO₂, and this is highly attractive to promote the economy and applicability of CO₂ utilization. This review focuses on recent advancements in the electrochemical reduction of CO₂ to formic acid, methanol, ethanol, acetic acid, and other oxygenates. The principles of the process, influencing factors, and typical catalysts are summarized. On the basis of the aforementioned discussions, we present future prospects for further development of the electroreduction of CO₂ to oxygenates.     

Carbon-based catalysts: Synthesis and applications

This paper summarizes the main results obtained by the Fuel Combustion Group in three applications: (1) carbon-based catalysts for the selective catalytic reduction (SCR) process of NO_x, (2) Pt and Pt–Ru catalysts for direct alcohol fuel cells, (3) carbon-supported catalysts for the electroreduction of CO₂. Concerning the first aspect, low-cost catalysts able to work at lower temperatures have been prepared and compared with commercial catalysts; for the second one, new catalysts for methanol and ethanol electrochemical oxidation exhibiting current densities that are double those of the commercial ones have been developed; as regards the third one, carbon-supported catalysts for the electroreduction of CO₂ based on Fe and Pd were synthesized and tested. Formic acid was obtained as the main product on all Fe/C electrodes.     

Supported molecular catalysts for the heterogeneous CO2 electroreduction

The thorough understanding of homogeneous catalysis has triggered intense research activities on the immobilization of molecular catalysts for the heterogeneous CO₂ electroreduction. Herein, we discuss recent advances in the heterogeneous field with focus on the intrinsic effect coming from the catalyst structure and the extrinsic effect exerted by the catalyst immobilization strategy and support material on the catalytic performance.     

Low‐Coordinated Edge Sites on Ultrathin Palladium Nanosheets Boost Carbon Dioxide Electroreduction Performance

Electrochemical conversion of carbon dioxide (CO₂) to value‐added products is a possible way to decrease the problems resulting from CO₂ emission. Thanks to the eminent conductivity and proper adsorption to intermediates, Pd has become a promising candidate for CO₂ electroreduction (CO₂ER). However, Pd‐based nanocatalysts generally need a large overpotential. Herein we describe that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number. Hexagonal Pd nanosheets with 5 atomic thickness and 5.1 nm edge length reached CO faradaic efficiency of 94 % at ?0.5 V, without any decay after a stability test of 8 h. It appears to be the most efficient among all of Pd‐based catalysts toward CO₂ER. Uniform hexagonal morphology made it reasonable to build models and take DFT calculations. The enhanced activity originates from mainly edge sites on palladium nanosheets.     

Metal-free Catalyst B2S Sheet for Effective CO2 Electrochemical Reduction to CH3OH

Considering the problems of high costs, low catalytic activity and selectivity in the metal-based catalysts for CO₂ electroreduction, we apply boron-containing metal-free B₂S sheet as an alternative to the traditional metal-based catalysts. Reaction energy calculations identify the preferred “Formate” pathway for CO₂ conversion to CH₃OH on B₂S, in which the thermodynamic energy barrier obtained by using the Computational Hydrogen Electrode model is 0.57 eV, and the kinetic energy barrier obtained by searching the transition states is 1.18 eV. Another possible reaction pathway, “RWGS+CO-hydro”, is suppressed and the hydrogen evolution reaction (HER) side reaction is nonspontaneous. Compared to Cu(211) with the highest catalytic activity among all transition metals, B₂S sheet exhibits a better catalytic activity with a lower overpotential for CO₂ reduction and a better selectivity that suppresses the non-target reaction.     

Two-dimensional Pt2P3 monolayer: A promising bifunctional electrocatalyst with different active sites for hydrogen evolution and CO2 reduction

Green hydrogen production and CO₂ fixation have been identified as the fundamental techniques for sustainable economy. The open challenge is to develop high performance catalysts for hydrogen evolution reaction (HER) and CO₂ electroreduction (CO₂ER) to valuable chemicals. Under such context, this work reported computational efforts to design promising electrocatalyst for HER and CO₂ER based on the swarm-intelligence algorithm. Among the family of transition-metal phosphides (TMPs), Pt₂P₃ monolayer has been identified as excellent bifunctional catalysts due to high stability, excellent conductivity and superior catalytic performance. Different from typical d-block catalysts, p-band center presented by P atoms within Pt₂P₃ monolayer plays the essential role for its reactivity towards HER and CO₂ER, underlining the key value of p-electrons in advanced catalyst design and thus providing a promising strategy to further develop novel catalysts made of p-block elements for various energy applications.     

Three-phase electrochemistry for green ethylene production

The electrochemical conversion of greenhouse gases (mainly CO₂ and CH₄) into ethylene has attracted worldwide attention. Compared with thermal cracking and dehydrogenation ethylene production processes, electrochemical ethylene production is an energy-saving and environmentally friendly process with high atom and energy economies. Great efforts have been made in enhancing the performance of electrochemical CO_x reduction and alkane dehydrogenation reactions in recent years. The complicated interactions between gas reactants, electrolytes, and catalysts force the three-phase interface mass transfer process an important issue in determining the electrochemical activity and product selectivity. Herein, we summarize the recent progresses on electrochemical ethylene production. Special attention has been paid to the principles for the design of gas–liquid–solid and gas–solid–solid three-phase interfaces and their influence on the electrochemical CO_x reduction and alkane dehydrogenation reactions. The comprehensive understanding of those different ethylene production reactions together from the perspective of the three-phase interface-related mass transfer process would provide new insights into the design of advanced electrochemical cells for green ethylene production.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N-doped Carbon Catalysts

Ni,N-doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen-coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni,N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Looking Back and Looking Ahead in Electrochemical Reduction of CO2

Electrochemical reduction of carbon dioxide (CO₂) to valuable organic compounds is promising as to recycling of carbon source of CO₂ and technical compatibility with systems using renewable energy resources. In recent years, considerable efforts have been devoted to the research field of CO₂ conversion using electrocatalysis. This personal account particularly focuses on the recent progress that has been achieved by the Ertl Center and a number of groups in South Korea that becomes one of the larger CO₂ emitters. The research trends of catalyst development divided into different categories according to the primary products are presented first. Afterwards, several studies on theoretical calculations and electrolytic reactors are reviewed taking into account the fundamental understanding and feasibility of the CO₂ electroreduction. Finally, a perspective on the challenges and needs in achieving the advanced level of research and development is presented.     

Design and Preparation of Electrocatalysts by Electrodeposition for CO2 Reduction

With the increasing emission of carbon dioxide (CO₂), the conversion and utilization of CO₂ have become a topic of increasing concern. Electrochemical CO₂ reduction reaction (CO₂RR) is an attractive and sustainable approach for solving energy and environmental problems. Design of efficient catalysts is crucial for achieving highly efficient CO₂RR. Different methods to prepare catalysts have been reported and used. Among them, electrodeposition is one of the common approaches, which has some obvious advantages, such as requiring simple equipment, environmentally benign. Especially, it can direct deposit catalysts on different substrates to prepare electrodes for CO₂RR. In this review, we discuss recent advances in design and preparation of the catalysts by electrodeposition and their applications in CO₂RR. Furthermore, the perspective of this promising area is also discussed.     

Regulation of Coordination Number over Single Co Sites: Triggering the Efficient Electroreduction of CO2

The design of active, selective, and stable CO₂ reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were prepared and their CO₂ electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two‐coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm^?2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h^?1, surpassing most reported metal‐based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO₂ to the CO₂^.? intermediate and hence enhances CO₂ electroreduction activity.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Nickel Doping in Atomically Thin Tin Disulfide Nanosheets Enables Highly Efficient CO2 Reduction

Engineering electronic properties by elemental doping is a direct strategy to design efficient catalysts towards CO₂ electroreduction. Atomically thin SnS₂ nanosheets were modified by Ni doping for efficient electroreduction of CO₂. The introduction of Ni into SnS₂ nanosheets significantly enhanced the current density and Faradaic efficiency for carbonaceous product relative to pristine SnS₂ nanosheets. When the Ni content was 5 atm %, the Ni‐doped SnS₂ nanosheets achieved a remarkable Faradaic efficiency of 93 % for carbonaceous product with a current density of 19.6 mA cm^?2 at ?0.9 V vs. RHE. A mechanistic study revealed that the Ni doping gave rise to a defect level and lowered the work function of SnS₂ nanosheets, resulting in the promoted CO₂ activation and thus improved performance in CO₂ electroreduction.     

Overall Carbon-neutral Electrochemical Reduction of CO2 in Molten Salts using a Liquid Metal Sn Cathode

An overall carbon-neutral CO₂ electroreduction requires enhanced conversion efficiency and intensified functionality of CO₂-derived products to balance the carbon footprint from CO₂ electroreduction against fixed CO₂. A liquid Sn cathode is herein introduced into electrochemical reduction of CO₂ in molten salts to fabricate core–shell Sn−C spheres (Sn@C). An in situ generated Li₂SnO₃/C directs a self-template formation of Sn@C. Benefitting from the accelerated reaction kinetics from the liquid Sn cathode and the core–shell structure of Sn@C, a CO₂-fixation current efficiency higher than 84 % and a high reversible lithium-storage capacity of Sn@C are achieved. The versatility of this strategy is demonstrated by other low melting point metals, such as Zn and Bi. This process integrates energy-efficient CO₂ conversion and template-free fabrication of value-added metal-carbon, achieving an overall carbon-neutral electrochemical reduction of CO₂.