Electronic devices process information and transduce energy with electrons, while biology performs such operations with ions and chemicals. To establish bio-device connectivity, we fabricate a redox-capacitor film from a polysaccharide (i.e., chitosan) and a redox-active catechol. We report that these films are rapidly and repeatedly charged and discharged electrochemically via a redox-cycling mechanism in which mediators shuttle electrons between the electrode and film (capacitance ≈ 40 F/g or 2.9 mF/cm2). Further, charging and discharging can be executed under bio-relevant conditions. Enzymatic-charging is achieved by electron-transfer from glucose to the film via an NADPH-mediated redox-cycling mechanism. Discharging occurs by electron-donation to O2 to generate H2O2 that serves as substrate for peroxidase-mediated biochemical reactions. Thus, these films offer the capability of inter-converting electrochemical and biochemical inputs/outputs. Among potential applications, we anticipate that catechol–chitosan redox-capacitor films could serve as circuit elements for molecular logic operations or for transducing bio-based chemical energy into electricity.