Direct Current Generation from NADH and l-Cysteine Using Carbon Fiber: Possible Uses in Biofuel Cells

Abstract

Abstract Carbon fibers were found to directly oxidize β-nicotinamide adenine dinucleotide reduced form (NADH) and l-cysteine and to generate current without any mediator when the fibers as anode were connected to a cathode. After the carbon fibers were washed with water, ethanol, toluene, ethanol, and water in order, and dried, the fibers were heated at 700 °C for 5 min under aeration in order to eliminate any binder, for reformation of the carbon fibers. The maximum current value reached 6.84 mA after 2 min, and the value gradually decreased to 1.0 mA after 45 min, when the anode equipped with carbon fibers of 103 mg in the electrolyte composed of 1 mM NADH in 0.2 M phosphate buffer (pH 8.0) was connected with the cathode in 0.2 M NaH2PO4. At this time, the amount of remaining NADH was 10.8% of the initial amount, and a second addition of 41.5 mg of NADH to again reach 1.0 mM was performed. At the endpoint, the amount of remaining NADH was 4.9% of the total amount of added NADH. The current efficiency was 85% and the total quantity of electricity was 16.5 C. The carbon fibers were found to have NADH oxidation activity; the two electrons released, accompanied by NADH oxidation, are assumed to be absorbed by the fibers as anode, after the electrons flowed to the cathode. The specific surface area and the graphite content was 91.8 m2 g−1 and about 50%, respectively. The carbon fibers are considered to be very useful for construction of biofuel to which dehydrogenases using NAD(P)+ as a cofactor could be applied.