**4. Conclusions**

Photobioelectrochemical systems have been studied for more than a decade. However, the heterogeneity of materials selected to build electrodes, as well as the many applications that they can achieve has led this research area to be in a relative state of chaos. The lack of standardization of terminology makes it difficult for researchers to learn from the work of others, which in turn slows down the development and improvement of cells that have the possibility of solving many environmental problems while adding value through electricity generation. The nomenclature system proposed in this work aims to contribute to solve this problem, so future reviews could be done more easily and gather more information about these devices.

Moreover, there are still several topics that remain unexplored to this day. There are no publications that report chemotrophic photobiocathodes which, based on the information available on their anodic versions, should present a synergic effect that could increase the performance of reduction reactions made by chemotrophic biofilms.

There are no reports of phototrophic photobioelectrodes. The notion of covering a semiconductor with phototrophic microorganisms can open the possibility of using biofilms as sensitizers. These hypothetical electrodes could function as tandem solar cells, in which phototrophic microorganisms would absorb one part of the solar spectrum and generate current while the semiconductor absorbs another part, generating more current and, possibly, a synergistic effect that remains to be observed.

Lastly, there are no comparisons between microbial photobioelectrochemical systems and microbial bioelectrochemical systems assisted with solar panels to generate their required bias by harnessing sunlight. It is important to know which systems are more energetically and economically efficient so further research can be focused on the technology that has more potential to generate benefit and thus be applied at an industrial scale.
