(727b) Systematic Material Design for Enzymatic Biofuel Cells

Enzymatic biofuel cells can use a variety of non-toxic fuels like glucose and ethanol, and have attracted attention as energy sources used near the body. One important issue to be addressed is their low power density caused by their low current density. Considering the high intrinsic activity of enzymes, combinations of enzymes and nanostructured materials enable to power portable devices. However, simply combining enzymes and nanostructured materials does not necessarily lead to high current density, and thus rational design of the electrode is necessary to fully utilize the high intrinsic activity of enzymes.[1]

Our approach focused on the rate-limiting step in enzyme electrodes. First, to overcome the rate-limiting step of electron conduction through the redox polymer, we proposed a high-surface-area three-dimensional biofuel cell electrode made of redox-polymer-grafted carbon black to decrease the electron conduction distance in the redox polymer. The effectiveness of this electrode was verified by experiments and a mathematical model.[2],[3] The model calculation also suggested the utilization of the entire electrode surface by the enzymes leads to an increase in the current density of two orders of magnitude to around 100 mA cm^−2.[3] Further studies, especially detailed experiments on enzyme adsorption, revealed several reasons of the gap between the current densities obtained by experiments and the model calculation. One reason is the deactivation of the enzymes upon physical adsorption on hydrophobic surface of carbon black. Surface modification of carbon black to make the surface hydrophilic was shown to be effective in reducing the physical adsorption, and combination of surface modification and immobilization of glucose oxidase using ammonium sulfate precipitation with crosslinking doubled the glucose-oxidation current density.[4] Design guidelines to further improve the current density will be discussed in the presentation.

References: [1] T. Tamaki, Top. Catal., 55, 1162 (2012). [2] T. Tamaki and T. Yamaguchi, Ind. Eng. Chem. Res., 45, 3050 (2006). etc. [3] T. Tamaki, T. Ito, T. Yamaguchi, Fuel Cells, 1, 37 (2009). [4] T. Tamaki, T. Sugiyama, M. Mizoe, Y. Oshiba, T. Yamaguchi, J. Electrochem. Soc., 161, H3095 (2014).