Ferric ion pair mediated biomass redox flow fuel cell and related chemical reaction kinetics study

Abstract

Here, a novel and low cost redox flow fuel cell that directly converts raw biomass to electricity at low temperature without utilizing any noble metal catalyst is reported. In this cell, Fe3+ ion, which has strong oxidizing power and is chemical stable, was directly utilized as an oxidant for biomass in anolyte. The reduced Fe2+ acted as charge carriers, transferring the electrons to the anode of the cell and being converted back to Fe3+ simultaneously. The degradation chemistry of the biomass from the oxidation reaction and the apparent oxidation kinetics were investigated using glucose as the biomass model compound. The results showed that glucose was decomposed to small organic molecules and even CO2, and the reaction rate was significantly affected by temperature and content of reactant. The apparent activation energy of the redox reaction is 127.85 kJ·mol−1 based on the linear relation equation at the initial stage of the reaction. And the preference conditions of the redox reaction are 100–110 °C, 0.2–0.5 mol·L−1 glucose and the mol ratio of C6H12O6/FeCl3 from 1:10 to 1:12. Meantime, a high potential (VO2)2SO4 solution was synthesized as catholyte which was regenerated by O2 in the present of small amount of HNO3. The power density and discharge current density of the biomass redox flow fuel cell could reach 125.7 mW·cm−2 and 314.2 mA·cm−2, respectively, which was about 755 times higher than the reported microbial fuel cell by utilizing glucose as substrate. This work provides a promising way for converting abundant natural biomasses, such as crop straws and bagasse, into electricity at low temperature (80–110 °C).