Improvement of output and lifetime is a problem for biofuel cells. A structure was adopted in which gelation mixed with agarose and fuel (fructose) was sandwiched by electrodes made of graphene-coated carbon fiber. The electrode surface not contacting the gel was exposed to air. In addition, grooves were added to the gel surface to further increase the oxygen supply. The power density of the fuel cell was examined in terms of the electrode area exposed to air. The output increased almost in proportion to the area of the electrode exposed to air. Optimization of the concentration of fuel, gel, and the amount of enzyme at the cathode were also examined. The maximum power density in the proposed system was approximately 121μW/cm2, an enhancement of approximately 2.5 times that in the case of using liquid fuel. For the power density after 24h, the fuel gel was superior to the fuel liquid.

In this study, we optimized the reforming of bilirubin oxidase (BOD) using graphene-coated carbon fiber woven fabric (GCFC) as an electrode, and The performance of the cathode in which synthesized 1-pyrene butyric acid N-hydroxysuccinimide ester (PBSE) and 2,5-dimethyl-1-phenyl-1-H-pyrrole-3-carbaldehyde (DPPC) were added, was evaluated. In addition, the prototype evaluation of the atmospheric-exposure-type ascorbic acid enzyme biofuel cell (AAEBFC) using the improved GCFC cathode was performed. The area of both the anode and cathode electrodes was 5mm × 5mm. No modification was performed to the anode, and only the cathode was coated with the enzyme BOD. In the work, for the AAEBFC using the BOD-modified cathode, an output of 238.5µW/cm2 was obtained at 0.245V. Further, in the AAEBFC using the DPPC-PBSE-BOD-modified cathode, an output of 338.8µW/cm2 was obtained at 0.292V. The output in this work was improved by approximately 1.4 times by the additives.

In this study, two modification methods that employ graphene-coated carbon fiber woven fabric (GCFC) as an electrode and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) as a mediator were used to evaluate cathode performance. In addition, a prototype of an atmosphere-exposed ascorbic-acid enzyme biofuel cell (AAEBFC) consisting of an improved GCFC cathode and ABTS was evaluated. No modification was made in the anode region, and only the cathode region was coated with the enzyme of bilirubin oxidase (BOD). As a result of implementing an ABTS-modified cathode in the AAEBFC, an output of 721μW/cm2 was obtained at 0.189V. When the gel thickness was changed, an output of 1200μW/cm2 was obtained at 0.17V. To the best of our knowledge, this is currently the highest reported output for an AAEBFC fueled by ascorbic acid.