Biofuel cells performed similarly to those conventional fuel cells are regarded as one of potential substitute for fossil fuel. Developments of biofuel cells demonstrate the advantages on reduction of greenhouse gas emissions as well as increasing energy security. Enzyme-based biofuel cells is one kind of the biofuel cells, enzyme-based biofuel cells convert chemical energy into electrical energy via specific enzymes as biocatalysts. Glucose oxidase and laccase were immobilized onto carbon

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... as bioanode and biocathode, respectively in enzyme-based biofuel cells system. Mediator and enzyme were mixed in phosphate buffer (pH 7) and citrate buffer (pH 5) solutions, respectively. A Nafion membrane117 was inserted to separate the two half cells. The power density with respect to different operating voltages was obtained with a glucose concentration of 10 mM. Potassium hexacyanoferrate III and ABTS (2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) as mediators were added to the bioanode and biocathode cell, respectively. Carbon nanoballs were coated on the carbon paper and enormous enhancement of power density was achieved. The power-voltage with the CNB surface modifying by using plasma was with oxygen bubbling in cathode directly in the cell achieved up to 0.114 V. The power density was 65.5 μW/cm 2 . The assembled enzyme-based biofuel cells were studied under nitrogen at 37 • C in bioanode.