Abiotic Carbon Fixation Schemes
For convenience, a schematic is presented in \ref{414319} to better illustrate the factors involved in efficiency calculations for both H2-mediated and EET-mediated carbon fixation. Faradaic efficiencies were not included in the derivations for biotic carbon fixations schemes because calculations are much simpler in that the efficiencies can be multiplied in front of the final expression, since there is only one electrolytic cell. We can consider an approach in which electrocatalysts are used to reduce CO2 to a primary product like formic acid, which can then be consumed by the microbe. This method obviates the need to introduce carbon fixation into an electrosynthetic microbe, which still represents a grand challenge in synthetic biology at the time of writing \citep{Antonovsky:2016bl}.
To understand the energetics of the abiotic carbon fixation approach, we have built a 2- cell circuit. The current from an idealized solar photovoltaic is split between 2 cells, one that is assigned to abiotic carbon fixation, while the other is assigned to microbial reduction of the initial product of carbon fixation from the first cell to a biofuel. The current from the panel is divided so that an adequate number of electrons are sent to the second cell to fully reduce the fixed carbon from the first cell to a biofuel.