A schematic is shown for the factors that affect the thermionic efficiency of the system, assumed to be at steady state with the primary product flux being \(\dot{C}\). Cell 1 is the primary fixation with Faradaic efficiency ξPfix, cell 2 is the biological fixation with Faradaic efficiency ξAdd of the total of the products made from the incoming primary productand ξC is used to denote the Faradaic efficiency of the desired fuel with respect to all products from the primary product.