**7. Conclusions**

Membrane proteins play an important role for biofuel conversion and photosynthesis, and the catalytic and electron transfer ability of the membrane proteins makes them attractive for applications in bioelectrocatalysis. Recent developments in bioelectrochemistry have provided the means to control and improve electron transfer rate between immobilised proteins and electrodes, stabilising the activity of immobilised enzymes. High surface areas of so-called 3D electrodes are able to increase the protein loading, which is desired for bioelectrocatalysis. Despite these enhanced performances, there is still the need to further optimise this technology for practical use in bioelectrocatalysis devices, especially for membrane enzymes. Combining several immobilisation strategies would provide possible solutions. Advances in characterisation techniques enable detailed characterisation of the structure of the electrode, the electron transfer process, catalytic activity and protein structure, which in turn provides an in-depth understanding of the catalytic reaction mechanism, aiding the rational design of the electrode interface for bioelectrocatalysis. Membrane proteins are known to be difficult to study and manipulate due to their amphiphilic nature. Preserving their stability and functionality is crucial for successful application of this technology. Recently developed redox polymers and hybrid vesicles, composed of lipids and block copolymers, are promising platforms to stabilise membrane proteins on the electrode surface. Using exoeletrogenic microorganisms for electrosynthesis and semi-artificial photosynthesis is an encouraging research direction, which will simplify time and cost related with protein purification processes. The ability of microorganisms to regenerate and self-replicate (at an energy cost), also removes the need to stabilise the biocatalyst. With synthetic biology, the microorganisms can be further engineered for diverse biofuel and chemical synthesis. However, the extracellular electron transfer kinetics might still be limiting the efficiency of the whole-cell based systems, especially when organisms are used that have not been optimised by evolution for extracellular electron transfer.

**Funding:** This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), grant numbers BB/T000546/1 and BB/S000704/1.

**Conflicts of Interest:** The authors declare no conflict of interest.
