Читать книгу Indoor Photovoltaics - Группа авторов - Страница 27

The electrochemical potential from biological sources can be converted to electric energy. Biologic sources have the advantage that the host continuously and actively recharges these power sources by eating and drinking or photosynthesis. Such a host for a biochemical converter can be a plant, an animal or a human.

The first research on the use of biochemical energy, such as adenosine triphosphate (ATP) in the human body, was the ATP powered nanomotor by Cornell University [34]. Voltree Power’s bioenergy harvester uses the electrochemical potential resulting from the different pH concentration between soil and a plant [35]. The output voltage was reported to reach 50 to 200 mV for an estimated short circuit current between 0.1 to 1 mA [36]. The induced voltage U for an output voltage Uʹ results from the Nernst equation

(2.13)

where R = 8.31447 Jmol^-1K^-1 denotes the molecular gas constant, F = 96485,34 C mol^-1 the Faraday constant, T the temperature, n the number of transmitted electrons and DpH the difference of both potentials.

Other than in some horticultural and agricultural applications, indoor bioelectrochemical potentials are almost solely found in animals and humans. Rasmussen and coworkers demonstrated a biofuel cell with a power of 55 μW, that was implanted in a cockroach [37]. The output voltage was 0.2 V. Such implantable fuel cells can work as an alternative to batteries or cabled solutions with a main application field in medicine. Technical challenges include the low output voltage of around 0.2–0.4 V and the size, stability and nontoxicity of the cathodes. A review of the design, the current state-of-the-art and challenges in biofuel cells has been provided by Zebda et al. [38].