Using the Tafel equation (10) showed the most obvious signs of sparseness of data to evaluate the potential to make EET-mediated systems viable, or abiotic photosynthesis with many of the products that people would wish to make. There was very limited data found for the substrates involved, with self-exchange currents found for CO and acetate, which were obtained by extrapolation from the studies that plotted Tafel plots for their electrochemical reductions. These values mainly pertain to the additional bias that overpotentials would contribute.
Figures 4A, B show increasing additional bias would decrease the overall efficiency. It seems In the EET-mediated system only fuphill of the electrons actually get promoted to reduce any carbon substrates in the form of NADH, that’s why \(H_2\)-mediated systems typically show less excess potential given the same current density one wishes to apply. However, the proportion to which the \(H_2\)-mediated bias is affected is less than that of the EET-mediated bias for the equivalent values. It should also be noted that the equivalent amount of additional bias that is put into the EET-mediated system results in greater efficiency losses as seen in Figure 4B. The option of using formate, a much more soluble source of electrons and hydrogen, is a viable bypass the \(H_2\) kinetics problem. However, this involves the usage of reduced carbon and its reversion to \(CO_2\), which was considered undesirable in this case, and hence unexamined.