Abstract
A biofuel cell (BFC) cathode has been developed based on direct electron transfer (DET) of hemoglobin (Hb) molecules with an indium-tin-oxide (ITO) electrode and their electrocatalysis for reduction of hydrogen peroxide (H2O2). In this study, the ITO-coated glass plates or porous glasses were prepared by using a chemical vapor deposition (CVD) method and examined the electrochemical characteristics of the formed ITO in pH 7.4 of phosphate buffered saline (PBS) solutions containing and not containing Hb. In half-cell measurements, the reduction current of H2O2 due to the electrocatalytic activity of Hb increased with decreasing electrode potential from around 0.1 V versus Ag|AgCl|KCl(satd.) in the PBS solution. The practical open-circuit voltage (OCV) on BFCs utilizing H2O2 reduction at the Hb-ITO cathode with a hydrogen (H2) oxidation anode at a platinum (Pt) electrode was expected to be at least 0.74 V from the theoretical H2 oxidation potential of −0.64 V versus Ag|AgCl|KCl(satd.) in pH 7.4. The assembled single cell using the ITO-coated glass plate showed the OCV of 0.72 V and the maximum power density of 3.1 µW cm−2. The maximum power per single cell was recorded at 21.5 µW by using the ITO-coated porous glass.
Highlights
Biofuel cells (BFCs) are clean and renewable power sources which directly convert chemical energy into electrical energy, typically utilizing the electrocatalytic functions of living cells, such as bacteria and algae or proteins and organelles extracted from the cells such as enzymes and mitochondria [1,2]
Since the potential range for the BFC based on direct electron transfer (DET) is generally close to the redox potential of the enzyme itself, it can be expected a high power-output as well as simplicity of the electrode compared with the mediated electron transfer (MET)-type BFCs
The BFC cathode utilizing the Hb-ITO system has some unique advantages: (i) it has potential for development of high performance BFC utilizing DET with a simple electrode structure; (ii) Hb is a low cost bio-material compared with other enzymes or rare metals such as bilirubin oxidase or platinum (Pt), and is renewable in the life circle of organizations; and (iii) as applied in an oxygen reduction cathode, which is proceeded with only two electron reduction producing H2O2 or totally four electron reduction consisting of two and two electron reduction to water, i.e., fully oxygen reduction via H2O2, it can be expected a promotive effect for the electrocatalysis of the electrode with four electron reduction of oxygen
Summary
Biofuel cells (BFCs) are clean and renewable power sources which directly convert chemical energy into electrical energy, typically utilizing the electrocatalytic functions of living cells, such as bacteria and algae or proteins and organelles extracted from the cells such as enzymes and mitochondria [1,2]. Since the potential range for the BFC based on DET is generally close to the redox potential of the enzyme itself, it can be expected a high power-output as well as simplicity of the electrode compared with the MET-type BFCs. most enzyme proteins show slow electron transfer characteristics with the electrodes. The BFC cathode utilizing the Hb-ITO system has some unique advantages: (i) it has potential for development of high performance BFC utilizing DET with a simple electrode structure; (ii) Hb is a low cost bio-material compared with other enzymes or rare metals such as bilirubin oxidase or platinum (Pt), and is renewable in the life circle of organizations; and (iii) as applied in an oxygen reduction cathode, which is proceeded with only two electron reduction producing H2O2 or totally four electron reduction consisting of two and two electron reduction to water, i.e., fully oxygen reduction via H2O2, it can be expected a promotive effect for the electrocatalysis of the electrode with four electron reduction of oxygen. We prepared ITO-coated glass plates and porous glasses by using a slightly customized chemical vapor deposition (CVD) method [39,40] to enhance the cathodic performance by enlarging the specific electrode surface area, and half-cell and single cell tests were carried out based on the reduction of H2O2 with the Hb-ITO system
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