The electrochemical reduction of carbon dioxide to various products is usually described as:
The redox potentials for these reactions are similar to that for hydrogen evolution in aqueous electrolytes, thus electrochemical reduction of CO is usually competitive with hydrogen evolution reaction.
Electrochemical methods have gained significant attention:
# at ambient pressure and room temperature;
# in connection with renewable energy sources (see also solar fuel)
# competitive controllability, modularity and scale-up are relatively simple.
The electrochemical reduction or electrocatalytic conversion of CO can produce value-added chemicals such methane, ethylene, ethanol, etc., and the products are mainly dependent on the selected catalysts and operating potentials (applying reduction voltage). 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. Many processes suffer from high overpotential, low current efficiency, low selectivity, slow kinetics, and/or poor catalyst stability.
The composition of the electrolyte can be decisive. Gas-diffusion electrodes are beneficial.