Enzyme Bioanode with Electropolymerized Thiazine for Formic Acid//O₂ Biofuel Cells

When and Where

Nov 30, 2022
3:30pm - 3:45pm

Hynes, Level 3, Room 303

Presenter

Motohiro Kosugi

Yuki Fujii

Ryoichi Tatara

Shinichi Komaba

Co-Author(s)

Motohiro Kosugi¹,Yuki Fujii¹,Ryoichi Tatara¹,Shinichi Komaba¹

Tokyo University of Science¹

Abstract

Motohiro Kosugi¹,Yuki Fujii¹,Ryoichi Tatara¹,Shinichi Komaba¹

Tokyo University of Science¹

An enzymatic biofuel cell (EBFC) is a type of power generating device where enzymes function as catalysts to oxidize biofuel (saccharides such as glucose or alcohols)[1]-[4] and reduce oxygen molecules.[5]-[7] It can be operated under mild conditions of neutral solution, room temperature and atmospheric pressure. The main advantage of an EBFC is the utilization of renewable energy sources through enzymatic reactions. Among the fuel sources currently available for EBFCs, formic acid is oxidized by formate dehydrogenase (FDH) at a low potential and is expected to high-voltage EBFCs. Most of the previously reported fuel cells with formic acid as the fuel utilize palladium or platinum as catalysts, and there are few reports of enzymes being used as catalysts. Using enzymes has the advantage of being relatively inexpensive compared to other catalysts in EBFCs. In this study, we focused on FDH with nicotinamide adenine dinucleotide (NAD) as the active site and prepared enzymatic bioanodes modified with three different electropolymerized thiazine dyes, methylene blue (MB), thionine (Th), and Azure A (AA), as electrocatalyst and investigated their electrochemical properties. The bioanodes were prepared as follows: 1) carbon powders (carbon nanotube or sucrose-derived carbon) was dispersed in water with sodium polyglutamate as the binder and dropped on carbon-felt (CF) electrodes (thickness: 2 mm; diameter: 11 mm), then the carbon electrodes were modified with the three electropolymerized films, polyMB, polyTh, and polyAA, and 3) FDH solution was drop-cast on the electrodes. Electrochemical measurements were conducted at room temperature in the phosphate buffer solution (0.1 mol dm-3 PBS at pH = 7.0,) containing NAD (10 mmol dm-3) and sodium formate (0.15 mmol dm-3). At the prepared electrode, formate was anodically oxidized with FDH at the electropolymerized electrode, and the coenzyme NAD was simultaneously reduced to NADH. The oxidation of NADH by the electropolymerized thiazine was expected to proceed rapidly. We successfully observed an oxidation current at −0.05 V (vs. Ag/AgCl), generated by the anodic decomposition of formate ions, in the substrate solution. This confirms that the electrochemically deposited thiazine polymer can act as electrocatalyst for the series of above oxidation reaction as expected. Among three thiazine dyes, it was found that polyMB has the highest catalytic activity for NADH oxidation, yielding the highest oxidation current densities owing to the efficient electron transfer process. The comparison of the electrochemical properties of the bioanode prepared with CNT and pyrolytic sucrose-derived carbon will also be discussed in the presentation. References [1] S. Komaba, et al., Electrochemistry, 76, 55 (2008) [2] Y. Handa, S. Komaba, et al., ChemPhysChem, 15, 2145 (2014). [3] R. Yasujima, S. Komaba, et al., ChemElectroChem, 5, 2271, (2018). [4] R. Toda, S. Komaba et al., ChemElectroChem, 8, 4199 (2021). [5] K. Yamagiwa, S. Komaba, et al., J. Electrochem. Soc., 162, F1425 (2015). [6] K. Yasueda, S. Komaba, et al., J. Electrochem. Soc., 165, F1369 (2018). [7] R. Tatara, S. Komaba, et al., J. Electrochem. Soc., 168, 074506 (2021)