Artificial Gills for Robots

This study is part of our ongoing research into energetically autonomous robots. Different strategies can and have been employed to achieve energy autonomy, primarily depending on the application for which the agent is designed for. One such strategy is to employ the microbial fuel cell (MFC) technology, that allows the extraction of energy from real food substrates (plants, insects or marine crustaceans), through microbial degradation [Ieropoulos et al. 2005a,b; Melhuish et al. 2006]. Robots have been constructed, which employ MFCs as their power generator. To date, these robots have been used terrestrially and have employed atmospheric oxygen [Ieropoulos et al. 2005a,b; Melhuish et al. 2006].

This work looks at the possibility of using MFC power generation technology underwater. In this way, one could envisage organic matter used as the biomass ‘fuel’ for the bacteria and oxygen used in an aqueous cathode. In some ways, the latter can be likened to an artificial gill.

MFCs comprise two half-cells; an anode and a cathode, which are necessary for the electricity-generating redox (reduction-oxidation) reactions to take place. The anode half-cell contains the bacterial cultures that generate the electricity and is therefore the negative terminal of the MFC. The cathode half-cell, is the positive terminal of the MFC that closes the ‘circuit’ for the electricity to flow. In general, there are two types of MFC cathodes commonly used; a chemically enhanced cathode system based on ferricyanide and a gas diffusion cathode system based on oxygen.