Among such efficient sustainable energy sources, as wind and solar power, photovoltaics, geothermal and water power and other1-3, biofuels are ranked as less efficient. The latest 2009 report of the International Energy Agency4 plans approximately 100% increase of the contribution of the renewable energy sources in the world energy consumption within the period from 2006 to 2030, with a biomass conversion mentioned only briefly. Along with this, the expedient development of new bioenergy technologies may change the future role of biological sources. One example is production of bioethanol as alternative fuel5,6; another example is a steadily expanding field of biofuel cells development7-10, with a number of scientific publications and patent applications increased more than 40 times during the last decade11. In terms of sustainable energy production, enzymatic biofuel cells are attractive for a number of special applications, such as disposable implantable power suppliers for medical sensor-transmitters and drug delivery/activator systems and self-powered enzyme-based biosensors; they do offer practical advantages of using abundant organic raw materials as biofuels for clean and sustainable energy production (1,2). In this paper we discuss what power densities can be expected from the enzymatic biofuel cells and what are the possibilities and limits for their optimization on the example of the designed in this work hybrid biofuel cell formed by the battery-type Zn anode and the biocathode, comprising horseradish peroxidase (HRP) immobilized on graphite and utilizing H2O2 as an oxidizer (3). The cell yields the open-circuit voltage Voc of 1.68 and 1.57 V and the short-circuit current density isc of 800 A cm-2 at pH 6 and 580 A cm-2 at pH 7.45, in quite solutions. The biofuel cell operated at 1.5 V for 6 days; the maximum power density of the cell was 98 W cm-2 at 0.6 V and pH 6. When coupled to the H2O2-producing glucose oxidizing enzymes (glucose oxidase or pyranose oxidase), the HRP-biocathode could function in the presence of glucose with no essential loss in I - V characteristics. The biocathode performance and possibilities for its optimization were studied and compared with the hitherto existing biocathodes and biofuel cell designs.
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1st International Conference on Bioinspired Materials for Solar Energy Utilization, 2011