A simple biofuel cell cathode with human red blood cells as electrocatalysts for oxygen reduction reaction

• This work first reported biofuel cell cathode with red blood cells (RBCs) as electrocatalysts for oxygen reduction reaction (ORR).
• RBCs showed “simple” direct electron transfer (DET) activity.
• A large ORR current by RBCs could be associated with practical application for body implantable power supplies.
• RBCs not strongly adsorbed on an ITO electrode surface.
• Single cell showed open circuit voltage of 0.43 V and maximum current density of 11 μA cm−2.

A red blood cell (RBC) from human exhibited direct electron transfer (DET) activity on a bare indium tin oxide (ITO) electrode. A formal potential of −0.152 V vs. a silver–silver chloride saturated potassium chloride (Ag|AgCl|KCl(satd.)) was estimated for the human RBC (type AB) from a pair of redox peaks at around 0.089 and −0.215 V (vs. Ag|AgCl|KCl(satd.)) on cyclic voltammetric (CV) measurements in a phosphate buffered saline (PBS; 39 mM; pH 7.4) solution. The results agreed well with those of a redox couple for iron-bearing heme groups in hemoglobin molecules (HbFe(II)/HbFe(III)) on the bare ITO electrodes, indicated that DET active species were hemoglobin (Hb) molecules encapsulated by a phospholipid bilayer membrane of the human RBC. The quantity of electrochemically active Hb in the human RBC was estimated to be 30 pmol cm−2. In addition, the human RBC exhibited oxygen reduction reaction (ORR) activity in the dioxygen (O2) saturated PBS solution at the negative potential from ca. −0.15 V (vs. Ag|AgCl|KCl(satd.)). A single cell test proved that a biofuel cell (BFC) with an O2|RBC|ITO cathode showed the open-circuit voltage (OCV) of ca. 0.43 V and the maximum power density of ca. 0.68 μW cm−2.