Superior pseudocapacitive behavior of confined lignin nanocrystals for renewable energy-storage materials

Strong demand for high-performance energy-storage devices has currently motivated the development of emerging capacitive materials that can resolve their critical challenge (i.e., low energy density) and that are renewable and inexpensive energy-storage materials from both environmental and economic viewpoints. Herein, the pseudocapacitive behavior of lignin nanocrystals confined on reduced graphene oxides (RGOs) used for renewable energy-storage materials is demonstrated. The excellent capacitive characteristics of the renewable hybrid electrodes were achieved by synergizing the fast and reversible redox charge transfer of surface-confined quinone and the interplay with electron-conducting RGOs. Accordingly, pseudocapacitors with remarkable rate and cyclic performances (∼96 % retention after 3000 cycles) showed a maximum capacitance of 432 F g^-1, which was close to the theoretical capacitance of 482 F g^-1 and sixfold higher than that of RGO (93 F g^-1). The chemical strategy delineated herein paves the way to develop advanced renewable electrodes for energy-storage applications and understand the redox chemistry of electroactive biomaterials. Renewable hybrid energy-storage materials were fabricated by confining pseudocapacitive biopolymer nanocrystals on graphene surfaces, showing high specific energy and power densities due to the fast and reversible pseudocapacitive behavior of bioinspired quinone moieties and their synergistic interplay with electron-conducting reduced graphene oxides.