Enzymatic fuel cell technology for energy production from bio-sources

Enzymatic biofuel cells (EFCs) are bioelectronic devices that use oxidoreductase enzymes as electrocatalysts for the oxidation of an organic substrate and/or the reduction of oxygen or peroxide, finalized to direct energy conversion to electricity. Enzymes provide excellent specificity towards the substrates, avoiding, in some cases, the need of membranes and noble metals, thus realizing very compact systems suitable for miniaturization. Other advantages include high catalytic activity with low overvoltage for substrate conversion, mild operating conditions, like ambient temperature and near-neutral pH and low cost. EFCs can be utilized in a variety of applications, which need low power input and the biocompatibility of the device, including implantable or wearable biofuel cells, self-powered biosensors and, generally, portable battery-free power solutions. For enzymatic biofuel cell design, an effective immobilization of enzymes on the electrodes is an important challenge to obtain direct electron transfer without mediators, resulting in higher performance and improved long term stability. The use of conductive nanomaterials and different types of polymers as electrodes allow to achieve high specific surface, increasing the number of wired enzymes per volume unit, and facilitate the electron transfer between enzyme active site and electrode. The present paper focuses on glucose fuel cells (GFCs), a subtype of conventional EFCs able to oxidize glucose provided by a lot of metabolic processes. The designs of bioanodes are focused on the use of glucose oxidase (GOx), while biocathodes are based on laccase. The realization of a preliminary prototype on lab scale is presented based on glucose oxidase immobilized on conductive polymer, which already exhibited stability over time (several months) once immobilized through innovative techniques. Since glucose is an essential, relatively abundant and almost unlimited source of energy in living organisms, possible applications are the development of implantable GFCs as well as the exploitation of agro-industrial wastes.