Electrochemical reduction of carbon dioxide to ethylene at a copper electrode in methanol using potassium hydroxide and rubidium hydroxide supporting electrolytes

Recent Progress in Two-Dimensional Materials for Electrocatalytic CO2 Reduction

Electrocatalytic CO2 reduction (ECR) is an attractive approach to convert atmospheric CO2 to value-added chemicals and fuels. However, this process is still hindered by sluggish CO2 reaction kinetics and the lack of efficient electrocatalysts. Therefore, new strategies for electrocatalyst design should be developed to solve these problems. Two-dimensional (2D) materials possess great potential in ECR because of their unique electronic and structural properties, excellent electrical conductivity, high atomic utilization and high specific surface area. In this review, we summarize the recent progress on 2D electrocatalysts applied in ECR. We first give a brief description of ECR fundamentals and then discuss in detail the development of different types of 2D electrocatalysts for ECR, including metal, graphene-based materials, transition metal dichalcogenides (TMDs), metal–organic frameworks (MOFs), metal oxide nanosheets and 2D materials incorporated with single atoms as single-atom catalysts (SACs). Metals, such as Ag, Cu, Au, Pt and Pd, graphene-based materials, metal-doped nitric carbide, TMDs and MOFs can mostly only produce CO with a Faradic efficiencies (FE) of 80~90%. Particularly, SACs can exhibit FEs of CO higher than 90%. Metal oxides and graphene-based materials can produce HCOOH, but the FEs are generally lower than that of CO. Only Cu-based materials can produce high carbon products such as C2H4 but they have low product selectivity. It was proposed that the design and synthesis of novel 2D materials for ECR should be based on thorough understanding of the reaction mechanism through combined theoretical prediction with experimental study, especially in situ characterization techniques. The gap between laboratory synthesis and large-scale production of 2D materials also needs to be closed for commercial applications.

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.

Investigation on Electroreduction of CO2 to Formic Acid Using Cu3(BTC)2 Metal-Organic Framework (Cu-MOF) and Graphene Oxide

A recent class of porous materials, viz., metal-organic frameworks (MOFs), finds applications in several areas. In this work, Cu-based MOFs (Cu-benzene-1,3,5-tricarboxylic acid) along with graphene oxide, viz., Cu-MOF/GO, are synthesized and used further for reducing CO2 electrochemically. The reduction was accomplished in various supporting electrolytes, viz., KHCO3/H2O, tetrabutylammonium bromide (TBAB)/dimethylformamide (DMF), KBr/CH3OH, CH3COOK/CH3OH, TBAB/CH3OH, and tetrabutylammonium perchlorate (TBAP)/CH3OH to know their effect on product formation. The electrode fabricated with the synthesized material was used for testing the electroreduction of CO2 at various polarization potentials. The electrochemical reduction of CO2 is carried out via the polarization technique within the experimented potential regime vs saturated calomel electrode (SCE). Ion chromatography was employed for the analysis of the produced products in the electrolyte, and the results showed that HCOOH was the main product formed through reduction. The highest concentrations of HCOOH formed for different electrolytes are 0.1404 mM (-0.1 V), 66.57 mM (-0.6 V), 0.2690 mM (-0.5 V), 0.2390 mM (-0.5 V), 0.7784 mM (-0.4 V), and 0.3050 mM (-0.45 V) in various supporting electrolyte systems, viz., KHCO3/H2O, TBAB/DMF, KBr/CH3OH, CH3COOK/CH3OH, TBAB/CH3OH, and TBAP/CH3OH, respectively. The developed catalyst accomplished a significant efficiency in the conversion and reduction of CO2. A high faradic efficiency of 58% was obtained with 0.1 M TBAB/DMF electrolyte, whereas for Cu-MOF alone, the efficiency was 38%. Thus, the work is carried out using a cost-effective catalyst for the conversion of CO2 to formic acid than using the commercial electrodes. The synergistic effect of GO sheets at 3 wt % concentration and Cu+OH- interaction leads to the formation of formic acid in various electrolytes.

CO2 Reduction: From Homogeneous to Heterogeneous Electrocatalysis

Due to increasing worldwide fossil fuel consumption, carbon dioxide levels have increased in the atmosphere with increasingly important impacts on the environment. Renewable and clean sources of energy have been proposed, including wind and solar, but they are intermittent and require efficient and scalable energy storage technologies. Electrochemical CO₂ reduction reaction (CO₂RR) provides a valuable approach in this area. It combines solar- or wind-generated electrical production with energy storage in the chemical bonds of carbon-based fuels. It can provide ways to integrate carbon capture, utilization, and storage in energy cycles while maintaining controlled levels of atmospheric CO₂. Electrochemistry allows for the utilization of an electrical input to drive chemical reactions. Because CO₂ is kinetically inert, highly active catalysts are required to decrease reaction barriers sufficiently so that reaction rates can be achieved that are sufficient for electrochemical CO₂ reduction. Given the reaction barriers associated with multiple electron-proton reduction of CO₂ to CO, formaldehyde (HC(O)H), formic acid, or formate (HC(O)OH, HC(O)O^-), or more highly reduced forms of carbon, there is also a demand for high selectivity in catalysis. Catalysts that have been explored include homogeneous catalysts in solution, catalysts immobilized on surfaces, and heterogeneous catalysts. In homogeneous catalysis, reduction occurs following diffusion of the catalyst to an electrode where multiple proton coupled electron transfer reduction occurs. Useful catalysts in this area are typically transition-metal complexes with organic ligands and electron transfer properties that utilize combinations of metal and ligand redox levels. As a way to limit the amount of catalyst, in device-like configurations, catalysts are added to the surfaces of conductive substrates by surface binding, in polymeric films, or on carbon electrode surfaces with molecular structures and electronic configurations related to catalysts in solution. Immobilized, homogeneous catalysts can suffer from performance losses and even decomposition during long-term CO₂ reduction cycles, but they are amenable to detailed mechanistic investigations. In parallel efforts, heterogeneous nanocatalysts have been explored in detail with the development of facile synthetic procedures that can offer highly active catalytic surface areas. Their high activity and stability have attracted a significant level of investigation, including possible exploitation for large-scale applications. However, translation of catalytic reactivity to the surface creates a new reactivity environment and complicates the elucidation of mechanistic details and identification of the active site in exploring reaction pathways. Here, the results of previous studies based on transition-metal complex catalysts for CO₂ electroreduction are summarized. Early studies showed that transition-metal complexes of Ru, Ir, Rh, and Os, with well-defined structures, are all capable of catalyzing CO₂ reduction to CO or formate. Derivatives of the complexes were surface attached to conducting electrodes by chemical bonding, noncovalent bonding, or polymerization. The concept of surface binding has also been extended to the preparation of surface area electrodes by the chemically controlled deposition of nanostructured catalysts such as nano tin, nano copper, and nano carbon, all of which have been shown to have high selectivities and activities toward CO₂ reduction. In our presentation, we end this Account with recent advances and a perspective about the application of electrocatalysis in carbon dioxide reduction.

Electrolyte Effects on the Electrochemical Reduction of CO2

The electrochemical reduction of CO2 to fuels or commodity chemicals is a reaction of high interest for closing the anthropogenic carbon cycle. The role of the electrolyte is of particular interest, as the interplay between the electrocatalytic surface and the electrolyte plays an important role in determining the outcome of the CO2 reduction reaction. Therefore, insights on electrolyte effects on the electrochemical reduction of CO2 are pivotal in designing electrochemical devices that are able to efficiently and selectively convert CO2 into valuable products. Here, we provide an overview of recently obtained insights on electrolyte effects and we discuss how these insights can be used as design parameters for the construction of new electrocatalytic systems.

Electrochemical CO2 Reduction into Chemical Feedstocks: From Mechanistic Electrocatalysis Models to System Design

The electrochemical reduction of CO₂ is a promising route to convert intermittent renewable energy to storable fuels and valuable chemical feedstocks. To scale this technology for industrial implementation, a deepened understanding of how the CO₂ reduction reaction (CO₂ RR) proceeds will help converge on optimal operating parameters. Here, a techno-economic analysis is presented with the goal of identifying maximally profitable products and the performance targets that must be met to ensure economic viability-metrics that include current density, Faradaic efficiency, energy efficiency, and stability. The latest computational understanding of the CO₂ RR is discussed along with how this can contribute to the rational design of efficient, selective, and stable electrocatalysts. Catalyst materials are classified according to their selectivity for products of interest and their potential to achieve performance targets is assessed. The recent progress and opportunities in system design for CO₂ electroreduction are described. To conclude, the remaining technological challenges are highlighted, suggesting full-cell energy efficiency as a guiding performance metric for industrial impact.

Liquid Hydrocarbon Production from CO2 : Recent Development in Metal-Based Electrocatalysis

Rising levels of CO₂ accumulation in the atmosphere have attracted considerable interest in technologies capable of CO₂ capture, storage and conversion. The electrochemical reduction of CO₂ into high-value liquid organic products could be of vital importance to mitigate this issue. The conversion of CO₂ into liquid fuels by using photovoltaic cells, which can readily be integrated in the current infrastructure, will help realize the creation of a sustainable cycle of carbon-based fuel that will promote zero net CO₂ emissions. Despite promising findings, significant challenges still persist that must be circumvented to make the technology profitable for large-scale utilization. With such possibilities, this Minireview presents the current high-performing catalysts for the electrochemical reduction of CO₂ to liquid hydrocarbons, address the limitations and unify the current understanding of the different reaction mechanisms. The Minireview also explores current research directions to improve process efficiencies and production rate and discusses the scope of using photo-assisted electrochemical reduction systems to find stable, highly efficient catalysts that can harvest solar energy directly to convert CO₂ into liquid hydrocarbons.

High-efficiency synergistic conversion of CO2 to methanol using Fe2O3 nanotubes modified with double-layer Cu2O spheres

Cuprous oxide/hematite nanotubes (Cu2O/Fe2O3NTs) were prepared by a potentiostatic electrodeposited method, in which different structured Cu2O materials were modified onto Fe2O3 NTs surface. Among them, the material with double-layer Cu2O spheres (Cu2O/Fe2O3 NTs-30) showed excellent photoelectrocatalytic (PEC) properties with a suitable energy band gap (1.96 eV) and a smaller overpotential (0.18 V). Furthermore, Cu2O/Fe2O3 NTs-30 showed two types of synergisms in the PEC reduction of CO2: (i) between electrocatalysis and photocatalysis and (ii) between Cu2O and Fe2O3NTs. The faradaic efficiency and methanol yield reached 93% and 4.94 mmol L(-1) cm(-2) after 6 h, respectively.

A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels

This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO2) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO(-), CH2O, CH4, H2C2O4/HC2O4(-), C2H4, CH3OH, CH3CH2OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO2 electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution-electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO2 reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area.

Fixation of CO2 by electrocatalytic reduction and electropolymerization in ionic liquid-H2O solution

The electrocatalytic synthesis of low-density polyethylene (LDPE) from carbon dioxide on a nanostructured (ns)TiO2 film electrode was investigated by controlled potential electrolysis in a solvent mixture of water and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF4) at room temperature under ambient pressure. Under these conditions, the nsTiO2 film is remarkably efficient and selective for the electroreduction of CO2. The current efficiency for the formation of the electrolytic product is about 8-14% at -1.50 V (vs SCE). The electrocatalytic activity of the electrode in the electrochemical reduction of CO2 was investigated by cyclic voltammetry (CV), and the probable electrode reaction mechanism is discussed.