In enzymatic fuel cells the optimisation of the local environment could similarly improve the current performance of these bioelectrochemical devices. Low power output remains one of the key issues which hinders the wider application of enzymatic fuel cells. The densely porous electrodes employed in these systems, such as multi-walled carbon nanotubes, alongside the redox polymers often used to mediate electron transfer will lead to the development of large concentration gradients between the electrodes and the bulk. Whilst consideration of the substrate concentration across these electrodes has been made, the local pH and electrolyte composition has not been accounted for and therefore has the potential to significantly increase power output as shown here for bioelectrochemical fuel synthesis. The negative effect of the local pH increase in enzymatic CO2 reduction is enhanced compared to systems utilising synthetic catalysts as there is no concomitant beneficial change in selectivity against HER. This work demonstrates the increasing importance of studying enzymes as exemplary selective and specific molecular catalysts. As artificial molecular catalysts become more sophisticated, and hence more selective, the techniques and conclusions of this enzymatic research will become ever more applicable.