Formation of Hydrocarbons in the Electrochemical Reduction of Carbon Dioxide at a Copper Electrode in Aqueous Solution
TL;DR: In this article, the authors studied the effect of CO2 adsorption strength on the production of CO at the Cu electrode in aqueous inorganic electrolytes and compared the mechanism of the Fishcher-Tropsch reaction.
Abstract: Electroreduction of CO2 at Cu in aqueous inorganic electrolytes was studied by means of voltammetric, coulometric and chronopotentiometric measurements. CO, CH4, C2H4, EtOH and PrnOH are produced at ambient temperatures. Formation of CO predominates at less negative potentials (more positive than –1.2 V vs. NHE); hydrocarbons and alcohols are favourably produced below –1.3 V vs. NHE, where the Faradaic efficiency of CO drops. CO, formed as an intermediate from CO2, is adsorbed on the Cu electrode, interfering with cathodic hydrogen formation. The adsorption strength of CO on Cu is very weak as compared with that on Pt. Adsorbed CO is reduced to Hydrocarbons and alcohols at more negative potentials. The product distribution from CO2 depends strongly upon the electrolytes employed. Formation of C2H4 and alcohols is favoured in KCl, K2SO4, KClO4 and dilute HCO–3 solutions, whereas CH4 is preferentially produced in relatively concentrated HCO–3 and phosphate solutions. The product selectivity depends upon availability of hydrogen or protons on the surface, which is controlled by pH at the electrode. The pH at the electrode is greatly affected by the electrolyte, since OH– is released in the electrode reactions. The production of hydrocarbons and alcohols is discussed in comparison with the mechanism of the Fishcher–Tropsch reaction.
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TL;DR: This Perspective highlights several heterogeneous and molecular electrocatalysts for the reduction of CO2 and discusses the reaction pathways through which they form various products, including copper, a unique catalyst as it yields hydrocarbon products with acceptable efficiencies.
Abstract: The electrochemical reduction of CO2 has gained significant interest recently as it has the potential to trigger a sustainable solar-fuel-based economy. In this Perspective, we highlight several heterogeneous and molecular electrocatalysts for the reduction of CO2 and discuss the reaction pathways through which they form various products. Among those, copper is a unique catalyst as it yields hydrocarbon products, mostly methane, ethylene, and ethanol, with acceptable efficiencies. As a result, substantial effort has been invested to determine the special catalytic properties of copper and to elucidate the mechanism through which hydrocarbons are formed. These mechanistic insights, together with mechanistic insights of CO2 reduction on other metals and molecular complexes, can provide crucial guidelines for the design of future catalyst materials able to efficiently and selectively reduce CO2 to useful products.
1,396 citations
TL;DR: A solar energy based technology to recycle carbon dioxide into readily transportable hydrocarbon fuel (i.e., a solar fuel) would help reduce atmospheric CO2 levels and partly fulfill energy demands within the present hydrocarbon based fuel infrastructure.
Abstract: The past several decades have seen a significant rise in atmospheric carbon dioxide levels resulting from the combustion of hydrocarbon fuels. A solar energy based technology to recycle carbon dioxide into readily transportable hydrocarbon fuel (i.e., a solar fuel) would help reduce atmospheric CO2 levels and partly fulfill energy demands within the present hydrocarbon based fuel infrastructure. We review the present status of carbon dioxide conversion techniques, with particular attention to a recently developed photocatalytic process to convert carbon dioxide and water vapor into hydrocarbon fuels using sunlight.
1,357 citations
Cites background from "Formation of Hydrocarbons in the El..."
...While CO evolution is promoted in most of these materials, Cu facilitates reaction of CO and H2 to generate hydrocarbons, aldehydes, and alcohols as major products.(43,52,53) Of the various materials investigated as electrocatalysts, copper has been considered one of the most appropriate materials for the production of hydrocarbons and oxygenated hydrocarbons in aqueous solutions....
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TL;DR: In this paper, the authors investigated the reaction mechanism of the electrochemical reduction of carbon dioxide to hydrocarbons on copper electrodes using online mass spectrometry and showed that it is very likely that CHOads are the key intermediate towards the breaking of the C-O bond and, therefore, the formation of methane.
Abstract: We have investigated the reaction mechanism of the electrochemical reduction of carbon dioxide to hydrocarbons on copper electrodes. This reaction occurs via two pathways: a C1 pathway leading to methane, and a C2 pathway leading to ethylene. To identify possible intermediates in the reduction of carbon dioxide we have studied the reduction of small C1 and C2 organic molecules containing oxygen. We followed the formation and consumption of intermediates during the reaction as a function of potential, using online mass spectrometry. For the C1 pathway we show that it is very likely that CHOads is the key intermediate towards the breaking of the C–O bond and, therefore, the formation of methane. For the C2 pathway we suggest that the first step is the formation of a CO dimer, followed by the formation of a surface-bonded enediol or enediolate, or the formation of an oxametallacycle. Both the enediol(ate) and the oxametallacycle would explain the selectivity of the C2 pathway towards ethylene. This new mechanism is significantly different from existing mechanisms but it is the most consistent with the available experimental data.
708 citations
Cites background or methods from "Formation of Hydrocarbons in the El..."
...To investigate this, the electrochemical reduction of CO [23, 63, 64, 67, 76, 77] and HCOO − [67, 78] were separately performed in conditions comparable to that of electrochemical CO2 reduction....
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...The strong correlation between the change in selectivity from CH4 to C2H4 and the increase in pH was first documented in Hori’s various works [22, 43, 48, 67, 77]....
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...Another observation made but not given much attention at the time of discovery is that the onset potential of C2H4 formation is always consistently more positive than that of CH4 [65, 67, 77]....
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...This explains the observation of early potentiometric [80] and voltammetry [67] experiments, where CO was suggested to desorb easily when the electrolyte was stirred or purged with an inert gas to remove dissolved CO....
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...[43, 67] showed that in KCl and K2SO4, C2H4 and alcohols are much more selective than CH4 (C2H4/CH4 ratio of 4....
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TL;DR: In this article, the use of nanostructured materials for improving catalytic reactivity is analysed in the context of model reactions of O2 reduction, CO2 electroreduction and ethanol oxidation.
Abstract: The field of electrocatalysis has undergone tremendous advancement in the past few decades, in part owing to improvements in catalyst design at the nanoscale. These developments have been crucial for the realization of and improvement in alternative energy technologies based on electrochemical reactions such as fuel cells. Through the development of novel synthesis methods, characterization techniques and theoretical methods, rationally designed nanoscale electrocatalysts with tunable activity and selectivity have been achieved. This Review explores how nanostructures can be used to control electrochemical reactivity, focusing on three model reactions: O2 electroreduction, CO2 electroreduction and ethanol electrooxidation. The mechanisms behind nanoscale control of reactivity are discussed, such as the presence of low-coordinated sites or facets, strain, ligand effects and bifunctional effects in multimetallic materials. In particular, studies of how particle size, shape and composition in nanostructures can be used to tune reactivity are highlighted. New catalysis materials are required for electrochemical reactions that are vital for clean energy production and environmental remediation. The use of nanostructured materials for improving catalytic reactivity is analysed in this Review in the context of model reactions of O2 reduction, CO2 electroreduction and ethanol oxidation.
637 citations
TL;DR: In this article, the effects of the nanostructure of the copper surface and compare the effect of the fcc(111, fcc (100) and fcc-211) facets of copper on the energetics of the electroreduction of CO 2.
435 citations
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TL;DR: In this paper, the authors studied the effect of CO2 adsorption strength on the production of CO at the Cu electrode in aqueous inorganic electrolytes and compared the mechanism of the Fishcher-Tropsch reaction.
Abstract: Electroreduction of CO2 at Cu in aqueous inorganic electrolytes was studied by means of voltammetric, coulometric and chronopotentiometric measurements. CO, CH4, C2H4, EtOH and PrnOH are produced at ambient temperatures. Formation of CO predominates at less negative potentials (more positive than –1.2 V vs. NHE); hydrocarbons and alcohols are favourably produced below –1.3 V vs. NHE, where the Faradaic efficiency of CO drops. CO, formed as an intermediate from CO2, is adsorbed on the Cu electrode, interfering with cathodic hydrogen formation. The adsorption strength of CO on Cu is very weak as compared with that on Pt. Adsorbed CO is reduced to Hydrocarbons and alcohols at more negative potentials. The product distribution from CO2 depends strongly upon the electrolytes employed. Formation of C2H4 and alcohols is favoured in KCl, K2SO4, KClO4 and dilute HCO–3 solutions, whereas CH4 is preferentially produced in relatively concentrated HCO–3 and phosphate solutions. The product selectivity depends upon availability of hydrogen or protons on the surface, which is controlled by pH at the electrode. The pH at the electrode is greatly affected by the electrolyte, since OH– is released in the electrode reactions. The production of hydrocarbons and alcohols is discussed in comparison with the mechanism of the Fishcher–Tropsch reaction.
1,135 citations