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.