Enzyme Biofuel Cells: Thermodynamics, Kinetics and Challenges in Applicability

In the last decade, several studies from different fields have contributed significantly to the development of the enzyme biofuel cell (BFC). Moreover, the design of biocatalyst-modified electrodes is a model for the development of synthetic and biomimetic electrocatalysts. The revival of the interest in the old BFC idea developed in the early 20th century is related to the development of new electrode materials as well as to the potential application of enzyme BFC miniaturisation in implantable bioelectronics. Furthermore, fundamental studies on half-cells and electron transfer involving protein film electrodes performed in the last few decades have established new types of electrodes for BFC applications. In terms of applicability, some research groups have sought to obtain unit cells with different properties and characteristics such as membrane-less BFCs by using flexible and low-costing materials; in addition, micrometric BFCs, which can be implanted in different body parts, have also been developed to supply electrical power to bioelectronics devices. Thus, in this review, we focus on introducing the main concepts and challenges in enzyme BFC research. Some important topics in kinetics and thermodynamics applied to BFCs are also discussed. Wherever possible, an extensive review of works undertaken in recent years is performed. The topics are organised into three major themes: thermodynamics, kinetics and challenges in applicability.