Polyoxometalate‐Mediated Lignin Oxidation for Efficient Enzymatic Production of Sugars and Generation of Electricity from Lignocellulosic Biomass

Abstract Conversion of lignocellulosic biomass to various renewable fuels, chemicals, materials, and electricity has attracted more and more interest in recent decades to decrease the dependence on fossil resources and reduce net CO 2 emissions. Herein, we have developed an integrated process of biomass pretreatment for enzymatic hydrolysis of cellulose coupled with electricity generation with polyoxometalates (POMs) and ferric ion as electron mediators and proton carriers. The pretreatment is a “charging” process, and the re‐oxidation of the POMs is effectively a “discharging” process. The pretreated substrate showed a good enzymatic digestibility (≈80 % cellulose conversion) within a short incubation period (<24 h). Fe 3+ was screened as a cheap, effective liquid mediator to transfer electrons to air, which is the terminal electron acceptor in the “discharging” process. The highest output power densities of 10.8 and 12.4 mW cm −2 were obtained for discharging of reduced H 3 PMo 12 O 40 and H 4 PMo 11 VO 40 , respectively. This power density is 5000–6000 times higher than that of phenol‐fueled microbial fuel cells, and 10 times higher than that of a recently reported direct biomass fuel cell with an air cathode covered with Pt catalyst. Moreover, this work also provides a conceptual combination of a direct biomass fuel cell and a redox flow cell, which can be flexibly switched between electricity generation from biomass and stationary energy storage.