**1.3 Photobioelectrochemistry**

The net energy generated by microbial electrolysis cells is significantly less than that of the microbial fuel cells due to the applied voltage that they require to work, which can represent up to 95% of the required operation energy of these devices [7]. To overcome this limitation, as well as improve energy generation, these systems have been modified either by adding photoelectrodes [14–16] or prototrophic microorganisms, which use light to drive their metabolism, [17] to harness the power of solar light. These new systems, for which an example is illustrated in **Figure 3**, have designs that integrate characteristics of photoelectrochemical and bioelectrochemical systems, generating a new field of study that will be called photobioelectrochemistry in this review.

Two other reviews address photobioelectrochemical systems. Both of them acknowledge that there is a new trend that integrates bioelectrochemical systems with photoelectrochemistry; however, their views do not clarify the potential scope that this field can have in terms of electrode materials and cell configurations [9, 18]. The present review aims to provide means to identify the whole set of

**Figure 3.** *A microbial photoelectrochemical cell with bioanode and photocathode.*

photobioelectrochemistry elements and analyze one of its subsets. To start defining photoelectrochemistry as its field, it is necessary to identify the electrode materials that it uses and find the proper terminology to refer to them.
