Electrochemical reduction of carbon dioxide
The electrochemical reduction of carbon dioxide (ERC) is the conversion of carbon dioxide to more reduced chemical species using electrical energy. The first examples of electrochemical reduction of carbon dioxide are from the 19th century, when carbon dioxide was reduced to carbon monoxide using a zinc cathode. Research in this field intensified in the 1980s following the oil embargoes of the 1970s. Electrochemical reduction of carbon dioxide represents a possible means of producing chemicals or fuels, converting carbon dioxide (CO
2) to organic feedstocks such as formic acid (HCOOH), methanol (CH3OH), ethylene (C2H4), methane (CH4), and carbon monoxide (CO).
Chemicals from carbon dioxideEdit
In carbon fixation, plants convert carbon dioxide into sugars, from which many biosynthetic pathways originate. The catalyst responsible for this conversion, RuBisCo, is the most common protein on earth. Some anaerobic organisms employ enzymes to convert CO2 to carbon monoxide, from which fatty acids can be made.
In industry, a few products are made from CO2, including urea, salicylic acid, methanol, and certain inorganic and organic carbonates. In the laboratory, carbon dioxide is sometimes used to prepare carboxylic acids. No electrochemical process involving CO2 has been commercialized.
The electrochemical reduction of carbon dioxide to CO is usually described as:
- CO2 + 2 H+ + 2 e− → CO + H2O
The redox potential for this reaction is similar to that for hydrogen evolution in aqueous electrolytes, thus electrochemical reduction of CO2 is usually competitive with hydrogen evolution reaction.
Electrochemical methods have gained significant attention: 1) at ambient pressure and room temperature; 2) in connection with renewable energy sources (see also solar fuel) 3) competitive controllability, modularity and scale-up are relatively simple. The electrochemical reduction or electrocatalytic conversion of CO2 can produce value-added chemicals such methane, ethylene, ethane, etc., and the products are mainly dependent on the selected catalysts and operating potentials (applying reduction voltage).
Although an electrochemical route to CO (or other chemicals) has not been commercialized, a variety of homogeneous and heterogeneous catalysts have been evaluated. Many such processes are assumed to operate via the intermediacy of metal carbon dioxide complexes. Generally speaking, the processes developed up to 2010 either had poor thermodynamic efficiency (high overpotential), low current efficiency, low selectivity, slow kinetics, and/or poor stability. In 2011, workers from Dioxide Materials and University of Illinois showed that the combination of two catalysts could eliminate the high overpotential  More recently, the same group showed that the process was stable for 6 months at over 90% selectivity. Studies have shown that a gas-diffusion electrode design could promote the reaction rate of electrochemical CO2 reduction to CO and multi-carbon products.
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