Printed Enzymatic Current Sources
Authors: Valkiainen Matti , Tuurala Saara , Smolander Maria , Kaukoniemi Otto-Ville 
Published: March 2011

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 demands

Biofuel 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.