Printed enzymatic glucose/air batteries: Performance, stability and mass-manufacturing: Dissertation

The enzymatic biofuel cell (EBFC) converts the chemical energy of biofuel into electricity via bioelectrochemical reactions. The use of enzymes confers many advantages over metal catalysts e.g. renewability and low toxicity. However, enzymes are fairly sensitive to changes in temperature, pH and moisture. For this reason, enzymes are typically immobilized on electrodes either by chemical or physical adsorption. The electrodes are usually immersed in a liquid cell containing an optimised electrolyte. Hence, the conventional EBFC configuration is not practical and for this reason, a new type of EBFC was developed. In this thesis, screen printed enzymatic electrodes (4-12 cm2) were fabricated on paper-based substrates using enzymatic inks creating thin (ca. 1 mm) and bendable EBFCs. The outcome of this thesis was a mass-manufacturable glucose/air biobattery that can be stored as dry and activated on demand by buffer. The power output of these biobatteries was on µW scale, however multiple suggestions for achieving higher performance are presented in this thesis. This biobattery could be integrated e.g. with low-power sensors, RFID tags or even cosmetic/medical skin patches. At the anode, commercial glucose oxidase (GOx) and in-house purified aldose dehydrogenase (ALDH) were studied. At the cathode, two in-house purified laccases from Trametes hirsuta (ThL) and recombinant Melanocarpus albomyces were studied as well as one industrial laccase (EcoL). The fabrication methods included ink formulation using different carbon supports, biocompatible binders and enzyme-mediator pairs. First printing trials were performed in the laboratory using multiple enzyme-mediator pairs mixed with a commercial carbon-based ink. After that, the manufacturing was scaled up using GOx and EcoL mixed with in-house prepared graphite-based inks. The printed EBFCs were mainly characterised by means of electrochemistry. In the laboratory, the best power output (Pmax = 3.5 µW cm-2) was achieved with an ALDH/ThL cell, which had an open circuit voltage (OCV) of 0.62 V and maximum energy output (E) of ca. 10 µWh cm-2. The best GOx/ThL cell had an OCV of 0.38 V, Pmax of 1.4 µW cm-2 and E of 5.5 µWh cm-2. The pilot scale manufactured GOx/EcoL cells performed 50-90% less, which could be attributed to differences in the ink compositions as well as to the degradation of enzyme-mediator electrodes due to heating (23 °C vs. 70 °C) and storage (one day vs. one week). The stability of the printed enzymes (GOx and EcoL) was very good, they lost a maximum of 40% of their activity, regardless of the drying or storage temperature. However, when mediators were added into the inks, elevated drying temperatures accelerated the degradation, and 70-80% of the enzymatic activity was lost in 28 days. Moreover, the anode was found to be the limiting factor, and for this reason different approaches to increase the anode performance were tested.