2.3- Kinetics barrier
In general, \(H_2\)-mediated systems suffer from a large surface area required, even in the electrode model, despite the greater thermionic efficiency. Even at 100atm in the electrode model, we see a comparatively smaller improvement in Arequired almost 140\(m^2\) for a given area of a solar panel. However, these can be circumvented, and while it is possible that EET-mediated photosynthesis could offer better spatial convenience, further study is required to verify how close these approximations are to actual data.
2.3.1- Gas Pressure
the rate at which \(H_2\), and hence electrons and energy, are transported in both the ‘headspace’ model and the ‘electrode model’ depend on the partial pressure of \(H_2\). To investigate the kinetic barrier, the maximum thickness of the productive biofilm was measured at the required consumption rate of \(H_2\). Figures 5-A,B show the maximum thickness to maintain the flux of \(H_2\) required with the change in temperature for electrode and headspace models respectively. It is generally seen that the ‘electrode model’ allows for greater thicknesses of the film than the ‘headspace model’.
Here it can be seen that the thickness of the film is significantly increased using the electrode model, where even at 1atm, an order of magnitude of 1mm in thickness can be reached compared to 100μm in the headspace model, and the headspace requires roughly a 100-fold increase in pressure of \(H_2\) to viably have a film of 1mm. At room temperature, in the former case, with a current density of 0.32A \(m^{-2}\), an area of at least a 100-fold greater than that of the solar cell of interest is required, and the latter case, with a current density of 0.306 A \(m^{-2}\), at least a 1000-fold is required, meaning that spatially this may create challenges in setting up the experiment with a relatively large solar cell, or require significant amounts of pressure or increased cell density to drastically lower this spatial issue.
3.3.2- Gas solubility