Roots fuel cell produces and stores clean energy

In recent years, extensive scientific efforts have been conducted to develop clean bio-energy technologies. A promising approach that has been under development for more than a hundred years is the microbial fuel cell (MFC) which utilizes exo-electrogenic bacteria as an electron source in a bio-electrochemical cell. The viability of bacteria in soil MFCs can be maintained by integrating plant roots which release organic materials that feed the bacteria. In this work, we show that rather than organic compounds, roots also release redox species that can produce electricity in a bio-fuel cell. We first study the reduction of the electron acceptor Cytochrome C by green onion roots. We integrate green onion roots into a bio-fuel cell to produce a continuous bias-free electric current for more than 24 h in the dark. This current is enhanced upon irradiation of light on the onions leaves. We apply cyclic voltammetry and 2D-fluorescence measurements to show that NADH and NADPH act as major electron mediators between the roots and the anode, while their concentration in the external root matrix is increased upon irradiation of the leaves. Finally, we show that roots can contribute to energy storage by charging a supercapacitor.