Abstract
Direct electron transfer (DET), which requires no mediator to shuttle electrons from enzyme active site to the electrode surface, minimizes complexity caused by the mediator and can further enable miniaturization for biocompatible and implantable devices. However, because the redox cofactors are typically deeply embedded in the protein matrix of the enzymes, electrons generated from oxidation reaction cannot easily transfer to the electrode surface. In this review, methods to improve the DET rate for enhancement of enzymatic fuel cell performances are summarized, with a focus on the more recent works (past 10 years). Finally, progress on the application of DET-enabled EFC to some biomedical and implantable devices are reported.
Highlights
Since its first demonstration of concept by Yahiro et al (1964), enzymatic fuel cell (EFC) has gained much research interest as one of the environmentally friendly and renewable source of power generation
When an electron generated from oxidation catalyzed by the redox center of a bioanodic enzyme travels directly to the electrode surface and is collected as current, the enzyme is known to undergo direct electron transfer (DET); when an additional component is utilized between the enzymatic catalyst and electrode surface to act as a mediator to shuttle the electron, it is referred to as mediated electron transfer (MET)
Liu et al studied the effect of multiwalled carbon nanotubes (MWNTs) on the DET and electroactivity of GOx by co-depositing carbon nanotubes of various numbers of layers for various electroanalytical methods, which suggested that the electrons generated from GOx was shuttled from outer to inner wall of the MWNTs (Figure 3) (Liu et al, 2018)
Summary
Since its first demonstration of concept by Yahiro et al (1964), enzymatic fuel cell (EFC) has gained much research interest as one of the environmentally friendly and renewable source of power generation. When an electron generated from oxidation catalyzed by the redox center of a bioanodic enzyme travels directly to the electrode surface and is collected as current, the enzyme is known to undergo DET; when an additional component is utilized between the enzymatic catalyst and electrode surface to act as a mediator to shuttle the electron, it is referred to as MET. In an effort to increase this number and enhance the fuel cell performance utilizing DET, a number of components of EFC could be improved: protein engineering to increase the efficiency of the direct electron transfer; immobilization of the biocatalysts on the electrode to decrease the tunneling distance and enhance the stability; and use of functional nanomaterials as electrodes to maximize enzyme loading while minimizing IR drop and tunneling distance for efficient charge transfer. Methods to enhance the performance of DETenabled EFC that have recently been popular are summarized, and the outlook on these EFCs, including their applications are presented
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