Biological material is used to build up biological cathode electrodes (biological cathode) and biological batteries, particularly biological metal air batteries as well as biological flow battery. A biological battery system includes a reaction vessel, a medium, a conductive anode and a biological cathode electrode. The biological cathode has a conductive support layer, a polymeric binding layer disposed between the conductive support layer and a contact layer. The contact layer being configured to be in electrical contact with biological components in the medium or being deposited with biological components. When the reaction vessel is open to an ambient air, the biological components accept electrons from the cathode.