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.