title: A biofuel cell with electrochemically switchable and tunable power output.
abstract: An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.
authors.affiliation: Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Eugenii
authors.initials: E
authors.lastname: Katz
authors.forename: Itamar
authors.initials: I
authors.lastname: Willner
mesh_terms: D001674:Bioelectric Energy Sources; D003300:Copper / Q000737:chemistry*; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D004563:Electrochemistry / Q000379:methods; D004566:Electrodes; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000737:chemistry* / Q000378:metabolism; D005949:Glucose Oxidase / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D045542:PQQ Cofactor; D011758:Pyrroles / Q000737:chemistry* / Q000378:metabolism; D011804:Quinolines / Q000737:chemistry* / Q000378:metabolism; D015363:Quinolones / Q000737:chemistry* / Q000378:metabolism; D011809:Quinones / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D011758:Pyrroles; D011804:Quinolines; D015363:Quinolones; D011809:Quinones; C410406:pyrroloquinoline; D005182:Flavin-Adenine Dinucleotide; D045542:PQQ Cofactor; D003300:Copper; D005949:Glucose Oxidase; D005947:Glucose