Improvement of Total Capacity of a Lactate/Oxygen Biofuel Cell Based on a Three-Enzyme-Modified Carbon Cloth Electrode

Abstract

A biofuel cell using MgO-templated carbon (MgOC) is highly attention as a wearable power source1). A lactate/oxygen biofuel cell, in which lactate oxidase (LOx) is normally used, utilize two-electron oxidation of lactate to pyruvate 2). On the other hand, it is possible to improve the total capacity of the lactate/oxygen biofuel cells by using an enzyme cascadereaction3 ).In the present study, we developed a new biofuel cell that modifies pyruvate decarboxylase (PDC) and acetaldehyde dehydrogenase (ALDH) with LOx in anode. A total of four-electron oxidation reaction can be occurred from lactate to acetic acid via acetaldehyde. In this study, we examined the relationship between the battery capacity and the current density by enzyme cascade in detail.A carbon cloth was used as anode. 1,2-naphthoquinone, ALDH (20 units), PDC (40 units) and LOx (20 units) were dropped on the anode surface, successively. On the other hand, a MgO-templated carbon (MgOC)-coated carbon cloth was used as cathode. A bilirubin oxidase (BOD, 9 units) was immobilized on the MgOC-coated carbon cloth surface. The performance of the biofuel cell was evaluated by performing chronopotentiometry at a current density of 1 mA cm-2 and 2 mA cm-2. The electrolyte (50 mL) used was 1 mol dm-3 phosphate buffer (pH 7.0) containing 100 mmol dm-3 lactic acid.Figure 1 shows the chlonopotentiogram of the biofuel cell. It was confirmed that the open-circuit potential of the multi-enzyme-modified biofuel cell was increased compared with that of a conventional lactic acid biofuel cell [2]. The voltage of multi-enzyme-modified biofuel cell was firstly about 0.6 V and then gradually decreased to 0.4 V. Finally, the voltage was drastically dropped at 0 V after 330 s. On the other hand, a voltage of a biofuel cell, which only LOx was modified on the anode, was dropped at 150 s at 1 mA cm-2. The time to reach 0 V was shorter at 2 mA cm-2 at each anode, due to the drastically decrease of the substrate concentration of the electrode surface. From these results, it was indicated that the capacity of the biofuel cell was improved by the enzymatic cascade reactions.(1) A. Niiyama et al., Journal of Power Sources, 427, (2019), 49.(2) I. Shitanda et al., Journal of Power Sources, 436, (2019), 226844.(3) D. Sokic-Lazic et al., Electrochimica Acta, 56, (2011), 10772.Acknowledgements This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． Figure 1