Controllable oxidative depolymerization of lignin to produce aromatic aldehydes and generate electricity under mild conditions with direct biomass fuel cells as flexible reactors

Lignin was oxidized and depolymerized by a direct biomass fuel cell (DBFC) for electricity generation and production of aromatic aldehydes. The yield of aromatic aldehydes could be easily controlled by changing the anodic catalyst, cathodic oxidants and external loading. Cobalt and (VO2)2SO4 were screened as the most suitable anodic catalyst and cathodic oxidant, respectively. A maximum power density of 199.8 mW/cm2 was obtained under the optimized conditions for electricity generation; however, the yield of the aromatic aldehydes was greatly dependent on the type of lignin used, reaction conditions and the external loading (output voltage) of the DBFC. At a lignin concentration of 0.5 g/L, aromatic aldehydes yield of 7.8 % was obtained at an output voltage of 0.9 V. The formation of aromatic aldehydes was mainly caused by cleavage of beta-O-4 linkage and oxidation of side chains by the hydroxyl radicals formed via oxidation of OH- by Co3+ on the anode.