To date, copper is the only heterogeneous catalyst that has shown a propensity to produce valuable hydrocarbons and alcohols, such as ethylene and ethanol, from electrochemical CO2 reduction (CO2R). There are variety of factors that impact CO2R activity and selectivity, including the catalyst surface structure, morphology, composition, the choice of electrolyte ions and pH, and the electrochemical cell design. Many of these factors are often intertwined, which can complicate catalyst discovery and design efforts. Here we take a broad and historical view of these different aspects and their complex interplay in CO2R catalysis on Cu, with the purpose of providing new insights, critical evaluations, and guidance to the field with regard to research directions and best practices. First, we describe the various experimental probes and complementary theoretical methods that have been used to discern the mechanisms by which products are formed, and next we present our current understanding of the complex reaction networks for CO2R on Cu. We then analyze two key methods that have been used in attempts to alter the activity and selectivity of Cu: nanostructuring and the formation of bimetallic electrodes. Finally, we offer some perspectives on the future outlook for electrochemical CO2R.

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Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte

Product selectivity of photocatalytic CO2 reduction reactions

Electrochemical reduction of CO2 to high-energy-density oxygenates and hydrocarbons beyond CO is important for long-term and large-scale renewable energy storage. However, the key step of the C–C bond formation needed for the generation of C2 products induces an additional barrier on the reaction. This inevitably creates larger overpotentials and greater variety of products as compared to the conversion of CO2 to C1 products. Therefore, an in-depth understanding of the catalytic mechanism is required for advancing the design of efficient electrocatalysts to control the reaction pathway to the desired products. Herein, we present a critical appraisal of reduction of CO2 to C2 products focusing on the connection between the fundamentals of reaction and efficient electrocatalysts. An in-depth discussion of the mechanistic aspects of various C2 reaction pathways on copper-based catalysts is presented together with consideration of practical factors under electrocatalytic operating conditions. By providing som...

Understanding the Roadmap for Electrochemical Reduction of CO2 to Multi-Carbon Oxygenates and Hydrocarbons on Copper-Based Catalysts

Surface and Heterointerface Engineering of 2D MXenes and Their Nanocomposites: Insights into Electro- and Photocatalysis

Electrocatalytic reduction reaction of CO2 (CO2RR) is an effective way to mitigate energy and environmental issues. However, very limited catalysts are capable of converting CO2 resources into high-value products such as hydrocarbons or alcohols. Herein, we first propose a facile strategy for the large-scale synthesis of isolated Cu decorated through-hole carbon nanofibers (CuSAs/TCNFs). This CuSAs/TCNFs membrane has excellent mechanical properties and can be directly used as cathode for CO2RR, which could generate nearly pure methanol with 44% Faradaic efficiency in liquid phase. The self-supporting and through-hole structure of CuSAs/TCNFs greatly reduces the embedded metal atoms and produces abundant efficient Cu single atoms, which could actually participate in CO2RR, eventually causing -93 mA cm-2 partial current density for C1 products and more than 50 h stability in aqueous solution. According to DFT calculations, Cu single atoms possess a relatively higher binding energy for *CO intermediate. Therefore, *CO could be further reduced to products like methanol, instead of being easily released from the catalyst surface as CO product. This report may benefit the design of efficient and high-yield single-atom catalysts for other electrocatalytic reactions.

Scalable Production of Efficient Single-Atom Copper Decorated Carbon Membranes for CO2 Electroreduction to Methanol.

Surface and Interface Engineering in Copper-Based Bimetallic Materials for Selective CO2 Electroreduction

Most fundamental studies of electrocatalysis are based on the experimental and simulation results obtained for bulk model materials. Some of these mechanistic understandings are inapplicable for more active nanostructured electrocatalysts. Herein, considering the simplest and most typical electrocatalytic process, the hydrogen evolution reaction, an alternative reaction mechanism is proposed for nanomaterials based on the identification of a new intermediate, which differs from those commonly known for the bulk counterparts. In-situ Raman spectroscopy and electrochemical thermal/kinetic measurements were conducted on a series of nanomaterials under different conditions. In high-pH electrolytes with negligible hydronium (H3O+) concentration in bulk phase, massive H3O+ intermediates are found generating on the catalytic surface during water dissociation and hydrogen adsorption processes. These H3O+ intermediates create a unique acid-like local reaction environment on nanostructured catalytic surfaces and cut the energy barrier of the overall reaction. Such phenomena on nanostructured electrocatalysts explain their widely observed anomalously high activity under high-pH conditions. Most of the current understanding on electrocatalysis is obtained on bulk catalysts but has not been fully verified on nanostructured materials. An alternative alkaline hydrogen evolution reaction mechanism is proposed here for nanostructured catalysts.

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Anomalous hydrogen evolution behavior in high-pH environment induced by locally generated hydronium ions.

Copper is a significant platform for CO2 electroreduction catalysts because it is the only known metal to produce multi-carbon products but suffers from poor selectivity. In the early stages of the...

Selectivity Control for Electrochemical CO2 Reduction by Charge Redistribution on the Surface of Copper Alloys

https://onlinelibrary.wiley.com/doi/pdf/10.1002/sstr.202000058

Chaochen Xu

Papers

Surface and Interface Engineering in Copper-Based Bimetallic Materials for Selective CO2 Electroreduction

Anomalous hydrogen evolution behavior in high-pH environment induced by locally generated hydronium ions.

Selectivity Control for Electrochemical CO2 Reduction by Charge Redistribution on the Surface of Copper Alloys

Highly Selective Two-Electron Electrocatalytic CO2 Reduction on Single-Atom Cu Catalysts

Bronze alloys with tin surface sites for selective electrochemical reduction of CO2