Evaluation of Biofuel Cells with Hemoglobin as Cathodic Electrocatalysts for Hydrogen Peroxide Reduction on Bare Indium-Tin-Oxide Electrodes

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 <i>v</i><i>ers</i><i>us</i> 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 <i>versus</i> 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.