Progress in the Mechanisms and Materials for CO₂ Electroreduction toward C₂₊ Products

Abstract

Over the past decades, advances in science and technology have greatly benefitted the society. However, the exploitation of fossil fuels and excessive emissions of polluting gases have disturbed the balance of the normal carbon cycle, causing serious environmental issues and energy crises. Global warming caused by heavy CO2 emissions is driving new attempts to mitigate the increase in the concentration of atmospheric CO2. Significant efforts have been devoted for CO2 conversion. To date, the electroreduction of CO2, which is highly efficient and offers a promising strategy for both storing energy and managing the global carbon balance, has attracted great attention. In addition, the electrosynthesis of value-added C2+ products from CO2 addresses the need for the long-term storage of renewable energy. Therefore, developing catalysts that function under ambient conditions to produce C2 selectively over C1 products will increase the utility of renewable feedstocks in industrial chemistry applications. Recently, great progress has been made in the development of materials for electrocatalytic CO2 reduction (ECR) toward C2+ products; however, some issues (e.g., low selectivity, low current efficiency, and poor durability) remain to be addressed. In addition, the elementary reaction mechanism of each C2+ product remains unclear, contributing to the blindness of catalyst design. In this regard, the development of proposed mechanisms of ECR toward C2+ products is summarized herein. The key to generating C2+ products is improving the chances of C-C coupling. Test conditions significantly influence the reaction path of the catalyst. Thus, three different paths that that are most likely to occur during ECR to C2+ products are proposed, including the CO, CO-COH, and CO-CO paths. In addition, typical material regulatory strategies and technical designs for ECR toward C2+ products (e.g. crystal facet modulation, defect engineering, size effect, confinement effects, electrolyzer design, and electrolyte pH) are introduced, focusing on their effects on the selectivity, current efficiency, and durability. The four strategies for catalyst design (crystal facet modulation, defect engineering, size effect, and confinement effect) primarily affect the selectivity of the ECR via adjustment of the adsorption of reaction intermediates. The last two strategies for technique design (electrolyzer design and electrolyte pH) contributing greatly toward improving the current efficiency than selectivity. Finally, the challenges and perspectives for ECR toward C2+ products and their future prospects are discussed herein. Therefore, breakthroughs in the promising field of ECR toward the generation of C2+ products are possible when these catalyst design strategies and mechanisms are applied and novel designs are developed.

Stabilization of Cu+by tuning a CuO–CeO2interface for selective electrochemical CO2reduction to ethylene

“…5,6 The synthesis of valuable hydrocarbons and other chemicals through ECR has drawn significant attention as a potential scheme for recycling CO 2 . [7][8][9][10][11][12][13][14][15][16][17][18] In particular, C 2+ (containing two or more carbon atoms) compounds such as ethylene have high energy densities and enjoy global demand in comparison to C 1 products. 19,20 For instance, ethylene is widely used as an industrial feedstock for manufacturing plastics and diesel, and its selective production in lieu of methane is important.…”

Metal Oxide-Based Materials for Electrochemical CO₂ Reduction

“…Methane is commonly formed from the hydrogenation of *CO to *CHO species and its subsequent proton-electron transfer 30 . *CO can also dimerize to *COCO, which is the most accepted rout for C-C bond formation to yield C2 and C2+ hydrocarbons and oxygenates products 4,31,32 . Electrocatalysts are critical in these steps as well-designed electrocatalysts are beneficial for stabilizing the intermediates and lowering the energy barrier to reach high energy efficiency, and the selectivity of the reaction can also be tuned through the different binding strengths of intermediates on the catalyst surface 28 .…”

Facile synthesis of two-dimensional copper terephthalate for efficient electrocatalytic CO2 reduction to ethylene

“…In comparison to methane (CH 4 ) [11], carbon monoxide (CO) [12][13][14][15][16][17], or formic acid (HCOOH or formate [HCOO -] in alkaline electrolyte) [18,19] that are typically the major C 1 products of CO 2 reduction, converting CO 2 into C 2þ (encompassing two or more carbon atoms) hydrocarbons and oxygenates is desirable from both ecological and economic viewpoints [20][21][22][23]. Among various materials, Cu is the only active metal to electrochemically catalyse CO 2 into multi-electron transferred products because of its negative adsorption energy for CO Ã and positive adsorption energy for H Ã [24].…”