As described in Methodology and Simulation, the experimental system was also simulated using a FEM and the predicted current density shown as a dotted line over the experimental results (Figure ). Assuming a FE of 100%, the predicted H2 evolution is shown as separate bars in Figure . The simulated current densities were in close agreement to the experimental data for both the MES and MOPS electrolytes, supporting the validity of the model and its description of the enzyme kinetics, activity and solution mass transport. With the FEM matching the experimental conditions and outcomes, the model was then used to simulate the changes in local pH and buffer capacity within the electrode over time (Figure ), and as a function of distance from the electrode (Figure ).