A high-performance lignin flow fuel cell based on self-generating electricity of lignin at low temperature via a privileged structure and redox chemistry

The biomass flow fuel cell (BFFC) is a promising technology for realizing a sustainable society. However, BFFCs generally require electron mediators and complex pretreatment, resulting in miscellaneous ion pollution and energy consumption. Herein, we develop a lignin flow fuel cell (LFFC) for self-generating electricity via the privileged structure and redox chemistry of lignin without any electron mediators and pre-reaction. The experiments and theoretical simulations reveal that lignin can automatically release electrons by its oxidation and cleavage under a high voltage difference to achieve high cell performance. Interestingly, phenolic lignin model compounds with more methoxy groups exhibit higher cell performance because the methoxy groups can significantly reduce their HOMO–LUMO energy gaps and oxidation potentials, which is beneficial for releasing electrons. When industrial lignin was utilized as the fuel, the LFFC achieved a high power density of 159.9 mW cm−2 and worked stably for more than 8 h with 5.0 g lignin. Moreover, the LFFC fueled by 1.0 g lignin can output 219.9 mW h electrical energy, which is significantly higher than that of the reported BFFCs. Furthermore, the scale-up of the LFFC can power several electrical devices simultaneously at room temperature. This work provides a promising approach for next-generation LFFCs with low cost and high performance towards a sustainable future.