A mechanical rechargeable small-size microbial fuel cell with long-term and stable power output

Long-term and stable power output is a great challenge for small-size microbial fuel cell. In this study, a mechanical rechargeable microbial fuel cell was fabricated by combining strategies of “mechanical recharging” and auto-feeding to solve the issue of salt accumulation and achieve a long-term and stable power output. It was composed of a three-dimensional bioanode, an air-cathode, a replaceable sponge-electrolyte and a glass capillary auto-feeding channel. The mechanical rechargeable microbial fuel cell continuously generated a high voltage of over 450 mV across a 1000 Ω resistor for more than two weeks with the assistance of auto-feeding, and kept it up by replacing the sponge-electrolyte, also called “mechanical recharging”, periodically without using any external equipments and applying extra power, for example, an over 45-days’ operation at the stable voltage had been recorded. It was able to deliver a high maximum power density of over 2000 mW m−2 normalized to the projected area of air-cathode or 100 W m−3 normalized to the cell volume. Additional, this mechanical rechargeable microbial fuel cell showed higher Coulombic efficiency comparing to the separator-free aqueous electrolyte microbial fuel cell.