Electrofuels are high‐energy compounds produced by the electrochemical reduction of compounds such as carbon dioxide or water. Microorganisms can act as biocatalysts for these reactions, during which they accept electrons either directly or indirectly from electrodes in bioelectrochemical systems (BESs). These microbes store this electrical energy by producing extracellular compounds instead of biomass. The electricity that drives this process may be harvested from intermittent renewable sources such as solar or wind. Thus, electrosynthesis could simultaneously sequester CO 2 and store renewable energy sources in designer chemicals, materials, or in convenient, high‐energy dense fuels for use in our transportation and electrical grid sectors. Butanol appears to be an ideal electrofuel target because it is considered a “drop‐in” fuel that can be used in our current energy infrastructure. Several challenges still face the production of electrofuels. The stability, structure, and conductivity of materials used as electrodes, the efficiency of electron transfer between these electrodes and microbes, and the diffusion of substrates (e.g., CO 2 ) into and products (e.g., butanol) out of the microbes all need to be optimized for efficient microbial electrosynthesis. A complete life‐cycle assessment of the environmental impact of any electrofuel also needs to be conducted prior to its widespread use.

Electrofuels are high‐energy compounds produced by the electrochemical reduction of compounds such as carbon dioxide or water. Microorganisms can act as biocatalysts for these reactions, during which they accept electrons either directly or indirectly from electrodes in bioelectrochemical systems ( BESs ). These microbes store this electrical energy by producing extracellular compounds instead of biomass. The electricity that drives this process may be harvested from intermittent renewable sources such as solar or wind. Thus, electrosynthesis could simultaneously sequester CO 2 and store renewable energy sources in designer chemicals, materials, or in convenient, high‐energy‐dense fuels for use in our transportation and electrical grid sectors. Butanol appears to be an ideal electrofuel target because it is considered a “drop‐in” fuel that can be used in our current energy infrastructure. Several challenges still face the production of electrofuels. The stability, structure, and conductivity of materials used as electrodes, the efficiency of electron transfer between these electrodes and microbes, and the diffusion of substrates (e.g., CO 2 ) into and products (e.g., butanol) out of the microbes all need to be optimized for efficient microbial electrosynthesis. A complete life‐cycle assessment of the environmental impact of any electrofuel also needs to be conducted before its widespread use.