Michal Kizling

Biosupercapacitors for powering oxygen sensing devices

A biofuel cell comprising electrodes based on supercapacitive materials - carbon nanotubes and nanocellulose/polypyrrole composite was utilized to power an oxygen biosensor. Laccase Trametes versicolor, immobilized on naphthylated multi walled carbon nanotubes, and fructose dehydrogenase, adsorbed on a porous polypyrrole matrix, were used as the cathode and anode bioelectrocatalysts, respectively. The nanomaterials employed as the supports for the enzymes increased the surface area of the electrodes and provide direct contact with the active sites of the enzymes. The anode modified with the conducting polymer layer exhibited significant pseudocapacitive properties providing superior performance also in the high energy mode, e.g., when switching on/off the powered device. Three air-fructose biofuel cells connected in a series converted chemical energy into electrical giving 2 mW power and open circuit potential of 2V. The biofuel cell system was tested under various externally applied resistances and used as a powering unit for a laboratory designed two-electrode minipotentiostat and a laccase based sensor for oxygen sensing. Best results in terms of long time measurement of oxygen levels were obtained in the pulse mode -45 s for measurement and 15 min for self-recharging of the powering unit.

Reticulated vitreous carbon as a scaffold for enzymatic fuel cell designing

Three - dimensional (3D) electrodes are successfully used to overcome the limitations of the low space - time yield and low normalized space velocity obtained in electrochemical processes with two - dimensional electrodes. In this study, we developed a three - dimensional reticulated vitreous carbon - gold (RVC-Au) sponge as a scaffold for enzymatic fuel cells (EFC). The structure of gold and the real electrode surface area can be controlled by the parameters of metal electrodeposition. In particular, a 3D RVC-Au sponge provides a large accessible surface area for immobilization of enzyme and electron mediators, moreover, effective mass diffusion can also take place through the uniform macro - porous scaffold. To efficiently bind the enzyme to the electrode and enhance electron transfer parameters the gold surface was modified with ultrasmall gold nanoparticles stabilized with glutathione. These quantum sized nanoparticles exhibit specific electronic properties and also expand the working surface of the electrode. Significantly, at the steady state of power generation, the EFC device with RVC-Au electrodes provided high volumetric power density of 1.18±0.14mWcm-3 (41.3±3.8µWcm-2) calculated based on the volume of electrode material with OCV 0.741±0.021V. These new 3D RVC-Au electrodes showed great promise for improving the power generation of EFC devices.

Size Does Matter—Mediation of Electron Transfer by Gold Clusters in Bioelectrocatalysis

Metal nanostructures are often used in bioelectrocatalytic systems to increase the electrode surface area or to improve the conductivity of biofilms. We demonstrate, that decreasing the size of gold nanoparticles below 2 nm may result in a change of the mechanism of electron transfer (ET) between the enzyme active site and the electrode from direct to mediated ET. Clusters with diameters smaller than 2 nm exhibited molecule‐like behavior reflected in the appearance of oxidation and reduction peaks separated by a clearly developed HOMO—LUMO gap. The redox activity of the nanoparticles was found to contribute to the ET mechanism of fructose dehydrogenase switching it to gold cluster mediated electron transfer instead of direct ET. In the presence of gold clusters at the electrode, the overpotential of the catalyzed fructose oxidation reaction was 100 mV lower and the catalytic reaction rate constant was 2.5 times larger confirming the unique mediating role of the Au clusters.