Functionally Cooperating Mini-Generator: From Bacterial Fermentation to Electricity

Mini-generators based on Faraday's law have exploited a new application of self-propelled micromotors in energy conversion. However, most such mini-generators normally consume high-grade energy to produce low electric energy and lack applicable occasions. Herein, a mini-generator is designed that harvests low-grade internal energy of gas from a fermentation line for successive conversion to kinetic energy of reciprocating motions and finally to electric energy without harming the fermentation production. The problem of irregular release of fermentative bubbles resulting in disordered motions is solved by the design of a superhydrophobic cushion valve, which regulates bubble releases to ensure periodic surfacing-diving motions and stable electricity generation. The mini-generator has a lifetime over 20 000 s with the maximum induced voltage of 2.4 V, which is sufficient to light a dozen red LEDs and energy conversion efficiency reaches 40%. Moreover, the mini-generator is used back to the fermentation line as a real-time gas flowmeter. By integrating mini-generators with industrial fermentation lines, this work has provided an effective strategy to minimize energy input and maximize energy output of mini-generators by collecting weak environmental energy and meanwhile exploited practical uses of mini-generators with low output.