Ferricyanide and vanadyl (V) mediated electron transfer for converting lignin to electricity by liquid flow fuel cell with power density reaching 200 mW/cm2

Abstract Lignin is the most abundant aromatic compound in natural world and usually produced as a by-product in pulping industry and biomass biorefinery. To achieve direct and efficient conversion of lignin to electricity, we have constructed an electron transport chain mediated by several redox couples including [Fe(CN)6]3−/[Fe(CN)6]4−, VO2+/VO2+ and NO3−/NO, to promote the kinetics and efficiency of electron transfer from lignin to oxygen. [Fe(CN)6]3− could well extract electrons from corn stover alkaline lignin with 93–98% efficiency (based on the COD of lignin) at the weight ratio of lignin to K3Fe(CN)6 of 0.0121–0.0061:1. The formed ferrocyanide could be well re-oxidized in a liquid flow fuel cell with (VO2)2SO4 as the cathode electron carrier under the catalysis of HNO3. Under the optimal operation condition, a maximal peak power density of 200.3 mW/cm2 was achieved, being the highest among the reported results of various direct biomass fuel cells. The rate of electron transfer to air (oxygen) in cathode could be well improved by using an novel internal recycle reactor. About 90% of overall efficiency of electron transfer was achieved by this electron transport chain to convert the chemical energy of corn stover alkaline lignin to electric energy. The obtained results indicate that by using an acidic-alkaline asymmetric design under the assistance of proper electron carriers, the performance of the direct lignin fuel cell can be well improved. The finding of this work thus can provide a new route for highly-efficient generation of electricity from lignin.