Highly-efficient conversion of lignin to electricity by nickel foam anode loaded with solid electrocatalysts

Abstract

A novel liquid flow fuel cell with insoluble metal sulfides-modified nickel foam anodes was developed to achieve direct conversion of lignin to electricity under mild conditions, avoiding the separation problems caused by using soluble electron mediators. CoS has been screened as the most efficient anodic electrocatalyst for lignin oxidation in alkaline medium by Co2+/Co3+ redox couple. By using an alkaline anolyte-acidic catholyte asymmetric design with VO2+/VO2+ redox couple as the cathodic electrocatalysts, the highest peak power density of 176 mW/cm2 was obtained with sodium lignosulfonate as the fuel at 80 ℃. The anode showed excellent stability with a 97% selectivity over oxygen evolution reaction for at least four fed-batch operation without significant loss of the activity. Lignin underwent significant depolymerization and degradation primarily by cleavage of β-O-4′ aryl ether bond, while ring-opening reactions also took place to form aliphatic acids, and even a part of lignin was mineralized to CO2.