Ferric-ferrous redox couple mediated low temperature symmetric flow fuel cell for direct conversion of biomass residues into electricity

As one of promising candidates for high-efficient energy conversion device, biomass flow fuel cells (BFFCs) can directly convert biomass into electricity at low temperature without noble metal catalyst . Most BFFCs utilize polyoxometalates which are high molecular weight inorganic clusters with low molar solubility in water and relative high cost. Here we report a new, cheap and environmentally benign symmetric biomass flow fuel cell (BFFC) mediated by simple Fe 3+ /Fe 2+ redox couple on both sides, which can directly and efficiently convert various biomass residues into electricity at low temperature. Fe 3+ in anode can efficiently oxidize biomass residues into high value chemicals, such as 5-hydroxymethylfurfural, furfural , etc., and simultaneously being reduced to Fe 2+ . The low electric potential Fe 2+ in anode and the high electric potential Fe 3+ in cathode are assembled into a fuel cell. The consumed Fe 3+ in cathode can be regenerated immediately under the strong synergism of O 2 and HNO 3 . The designed cell yields a power density 54.5 mW cm −2 and can discharge continuously more than 7 h at a constant current density 200 mA cm −2 . The BFFC can successfully light 43 LED bubbles. This approach is highly desirable for the development of low cost, high-performance and environment-friendly biomass flow fuel cells.