Energy harvesting from organic liquids in micro-sized microbial fuel cells

Abstract

Micro-sized microbial fuel cells (MFCs) are miniature energy harvesters that use bacteria to convert biomass from liquids into usable power. The key challenge is transitioning laboratory test beds into devices capable of producing high power using readily available fuel sources. Here, we present a pragmatic step toward advancing MFC applications through the fabrication of a uniquely mobile and inexpensive micro-sized device that can be fueled with human saliva. The 25-μl MFC was fabricated with graphene, a two-dimensional atomic crystal-structured material, as an anode for efficient current generation and with an air cathode for enabling the use of the oxygen present in air, making its operation completely mobile and free of the need for laboratory chemicals. With saliva as a fuel, the device produced higher current densities (1190 A m−3) than any previous air-cathode micro-sized MFCs. The use of the graphene anode generated 40 times more power than that possible using a carbon cloth anode. Additional tests were performed using acetate, a conventional organic material, at high organic loadings that were comparable to those in saliva, and the results demonstrated a linear relationship between the organic loading and current. These findings open the door to saliva-powered applications of this fuel cell technology for Lab-on-a-Chip devices or portable point-of-care diagnostic devices. A micro-sized (75 ml) MFC with graphene anode and air cathode fueled by human saliva producing higher current densities (1190 A m−3) than any previous air-cathode micro-sized MFCs and generated 40 times more power than that possible with a carbon cloth anode. In microbial fuel cells, microorganisms in the anode compartment carry out a biochemical reaction that oxidizes the fuel. The electrons produced are transferred to the cathode compartment through an external circuit, generating an electrical current. The development of micro-sized microbial fuel cells is attractive owing to their potential for use in portable devices, such as point-of-care diagnostic units. A team of researchers led by Muhammad M. Hussain at the King Abdullah University of Science and Technology, Saudi Arabia, has now shown that multi-layered graphene serves as an efficient anode material for these devices. The graphene anode was prepared through chemical vapor deposition and combined with an air cathode — which enables the use of oxygen from the air — to produce a mobile 25-microliter microbial fuel cell. When saliva was used as a fuel, good power generation (of nearly 1 microwatt) was observed, holding promise for the development of biointegrated electronics.