Construction of electron transfer chains with methylene blue and ferric ions for direct conversion of lignocellulosic biomass to electricity in a wide pH range

Abstract To achieve direct conversion of lignocellulosic biomass to electricity, electron transfer chains (ETCs) were constructed with organic redox compounds and ferric ions as the anode and cathode electron carriers, respectively. Methylene blue (MB) was screened as a promising anode electron carrier with good redox properties and being capable of efficiently working under both acidic and alkaline conditions. Acid or alkali electrolyte played important roles in depolymerization of cellulose and lignin, as well as the deconstruction of biomass (wheat straw) cell wall; however, the presence of MB well facilitated the degradation of cellulose and solublization of wheat straw polymeric components. The reduced MB (MBH) could be well re-oxidized and discharged in a liquid-flow fuel cell (LFFC). The highest out-put power densities (Pmax) of the LFFC under acidic and alkali conditions reached 12.3 and 41.8 mW/cm2 with open circuit voltages of 560 and 1560 mV, respectively.