Matti Valkiainen

A comparison of glucose oxidase and aldose dehydrogenase as mediated anodes in printed glucose/oxygen enzymatic fuel cells using ABTS/laccase cathodes

Current generation by mediated enzyme electron transfer at electrode surfaces can be harnessed to provide biosensors and redox reactions in enzymatic fuel cells. A glucose/oxygen enzymatic fuel cell can provide power for portable and implantable electronic devices. High volume production of enzymatic fuel cell prototypes will likely require printing of electrode and catalytic materials. Here we report on preparation and performance of, completely enzymatic, printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks, enzyme and mediator. A comparison of cell performance using a range of mediators for either glucose oxidase (GOx) or aldose dehydrogenase (ALDH) oxidation of glucose at the anode and ABTS and a fungal laccase, for reduction of oxygen at the cathode, is reported. Highest power output, although of limited stability, is observed for ALDH anodes mediated by an osmium complex, providing a maximum power density of 3.5 μW cm(-2) at 0.34 V, when coupled to a laccase/ABTS cathode. The stability of cell voltage in a biobattery format, above a threshold of 200 mV under a moderate 75 kΩ load, is used to benchmark printed fuel cell performance. Highest stability is obtained for printed fuel cells using ALDH, providing cell voltages over the threshold for up to 74 h, compared to only 2 h for cells with anodes using GOx. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.

A mediated glucose/oxygen enzymatic fuel cell based on printed carbon inks containing aldose dehydrogenase and laccase as anode and cathode

Enzyme electrodes show great potential for many applications, as biosensors and more recently as anodes and cathodes in biocatalytic fuel cells for power generation. Enzymes have advantages over metal catalysts, as they provide high specificity and reaction rates, while operating under mild conditions. Here we report on studies related to development of mass-producible, completely enzymatic printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks containing mediators and laccase, for reduction of oxygen, or aldose dehydrogenase, for oxidation of glucose. Mediator performance in these printed formats is compared to relative rate constants for the enzyme-mediator reaction in solution, for a range of anode and cathode mediators. The power output and stability of fuels cells using an acidophilic laccase isolated from Trametes hirsuta is greater, at pH 5, than that for cells based on Melanocarpus albomyces laccase, that shows optimal activity closer to neutral pH, at pH 6. Highest power output, although of limited stability, was observed for ThL/ABTS cathodes, providing a maximum power density of 3.5 μWcm(-2) at 0.34 V, when coupled to an ALDH glucose anode mediated by an osmium complex. The stability of cell voltage above a threshold of 200 mV under a moderate 75 kΩ load is used to benchmark printed fuel cell performance. Highest stability was obtained for a printed fuel cell using osmium complexes as mediators of glucose oxidation by aldose dehydrogenase, and oxygen reduction by T. hirsuta laccase, maintaining cell voltage above 200 mV for 137 h at pH 5. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.

Printed Supercapacitor as Hybrid Device with an Enzymatic Power Source

Low cost printable power sources are needed e.g. in sensors and RFID applications. As manufacturing method printing techniques are preferred in order to keep the costs low. The materials should also be easily disposable. Enzymatic bio-fuel cells are an alternative for printable primary batteries. Since one drawback of bio-fuel cells is their low power, we have developed supercapacitors that can be combined with enzymatic bio-fuel cells to provide the power peaks necessary in the applications. The materials for the supercapacitors have been chosen to be compatible with the fuel cell and with printing methods, e.g. the activated carbon powder in the electrodes was bound with chitosan. As printing substrates we have used paperboards. The current collectors have been made of graphite and metal inks. Since the voltage requirement is limited to approximately 1 V, aqueous electrolytes have been used. Printed supercapacitors of various sizes have been prepared. The geometrical electrode areas have been between 0.5 and 2 cm2. The maximum feasible output current has been in the order of 50 mA corresponding to about 50 mW power. When the capacitor is used together with an enzymatic power source, the leakage current must be as low as possible. Typical leakage current values have been in the order of 10 µA.

Performance of a Printable Enzymatic Fuel Cell - Study on Mediated ThL Laccase Cathode

In this work the performance of a printed ThL laccase biocathode is studied utilizing different electrode substrates, compositions and enzyme activities. The results indicate that the performance of the manufactured biocathode can be optimized by selecting a suitable substrate material and increasing the enzyme and mediator loading. By varying the substrate material app. 40 % increase in the cell performance was achieved. In addition by adding ten times higher amount of enzyme and mediator increased the cell performance app. 20 %.

Diffusivity and Porosity in Rock Matrix—Laboratory Methods Using Artificial and Natural Tracers

The nature of diffusivity and porosity in crystalline rock was studied by electrical conductivity measurements, steady-state diffusion experiments, saturation-leaching of tracers with cylindrical rock samples and analysis of the concentrations of different elements from core samples or pore water near fractures. The phenomena of main interest were dead-end porosity, ion-exclusion, sorption, and the continuity of pore networks. The modelling of experimental results was based on a modified Fick`s second law for diffusion, which was solved either by analytical or numerical methods. The measured D{sub e} and {epsilon} were found to statistically follow an exponential presentation: Archie`s law. The existence of ion-exclusion for anions was confirmed. The connectivity of the pore network extended in the laboratory experiments at least six centimetres, in coarse of the pore network extended in the laboratory experiments at least six centimetres, in coarse-grained granite in nature several metres but in fine-grained rock samples of a uranium deposit the element mobilization effects could be seen only to the depth of 2-3 centimetres.

Diffusivity and Porosity in Rock Matrix Related to the Ionic Strength in the Solution

The nature of diffusivity and porosity in rock was studied as a function of various parameters. The phenomena of main interest were dead-end porosity, ion-exclusion and sorption. The rock types studied were rapakivi granite, granite and gneiss, and tracer techniques with 36 Cl, 22 Na + and 3 H (HTO) were used as a research method. A mathematical solution for outdiffusion from a porous cylinder was developed by applying a corrected form of Ficks second law for a case where part of the pores are so-called dead-end pores. With this model the theoretical curve could be closely fitted to the measured values. It was found that the rock-capacity factor is an increasing function of the ionic concentration of the solution in the case of Cl indicating ion-exclusion, while the opposite is true in the case of Na + indicating ion-exchange type sorption. The effective diffusion coefficient was also found to vary as a function of the salinity in the case of 36 Cl. In the case of 22 Na, the effect was opposite and weaker. The diffusion of tritium through the rock samples was clearly higher than the diffusion of 36 Cl. Part of the difference is explained by the smaller effective porosity for 36 Cl. The rest can probably be explained by the steric effects on the chloride ion caused by the negatively charged pore surfaces in the narrow pores.

Chapter 1:Printed Enzymatic Current Sources

One of the main requirements for a power source to be used together with mass marketed package integrated functionalities (sensors, displays or entertaining features etc.) or as part of diagnostic devices is that the power source should be disposable or recyclable with normal household waste. This demand is not easily met by traditional battery technology. The material costs of the power source should also be reasonable, not to significantly increase the price of the product. The possibility to utilise biological catalysts, enzymes as the active components of a printed power sources i.e. biofuel cells has been found to have the potential to be developed to meet these demandsBiofuel cells are devices capable of transforming chemical energy directly to electrical energy via electrochemical reactions involving enzymatic catalysis replacing precious metal catalysts. Operational principles are the same in biofuel cells and in conventional fuel cells, but the operating conditions, catalysts, materials, as well as fuels utilized differ considerably from the conventional fuel cells. In an enzymatic biofuel cell various oxidising and reducing enzymes, i.e. oxidoreductases are applied as biocatalysts for the anodic or cathodic half cell reactions. Biofuel cells are a subject of intensive research to overcome the scientific and engineering challenges on the way from laboratory to the anticipated applications. The use of biofuel cells has been proposed for various applications, including miniaturised electronic devices, self-powered sensors and portable electronics. It is also anticipated that implanted biofuel cells could utilise body fluids, particularly blood, as the fuel source for the generation of electrical power, which may then be used to activate pacemakers, insulin pumps, prosthetic elements, or biosensing systems.In this chapter the possibility to utilise biological catalysts, enzymes, as the active components of a printed power sources i.e. biofuel cells is discussed. As a background, the biofuel cell constructions are presented in three different categories: biofuel cells constructed in a liquid chamber, biofuel cells based on carbon fibre design and biofuel cell constructions suitable for large scale production. Different biofuel cell structures and their potential construction or manufacturing methods are discussed and the performance of the different biofuel cell constructions is reviewed.Several printing techniques offer possibilities in the manufacturing of thin power sources, the important thing being the structure of the printed layer. Basically, several different printing methods are in principle suitable for the production of bioelectrochemically active layers with high reproducibility and possibility of mass-production and long-term storage stability. Potential printing methods and existing applications of power sources are discussed generally. Examples of mass-producible applications particularly involving the use of printed enzymes are also presented.The feasibility of the concept for printed enzyme catalyzed fuel cells has also been demonstrated by the authors of this chapter and is described. Particularly, the principle of the power source, ink formulation, stability, structure, manufacturing and performance of this novel, enzyme based power source are discussed.