Would it be possible, in principle, to create a machine that digests food in a similar way as humans do, extracts energy from the food, and stores it as electrical energy in a battery to power its own function? I understand this might be impractical or inefficient compared to other technologies, but I am just curious to know if it's something that can be done. (Not sure if I should ask here or on Chemistry Stack Exchange, really...)
Here they seem to be working on robots which digest insects:
But the robots also have a taste for flesh. They can gain energy by chomping on flies and mice, an idea inspired by researchers at Bristol Robotics Lab, UK, who built a fly-powered robot and have also suggested that marine robots could feed on plankton.
The pests are lured in and digested by an internal microbial fuel cell. This exploits the way microbes generate free electrons and hydrogen ions when oxidising chemicals for energy. Electronics can be powered by directing the electrons around an external circuit before reuniting them with the ions.