Laser-assisted Preparation of Vertically Aligned Reduced Graphene Oxide/tannic Acid Arrays for Flexible Aqueous Zinc-Ion Hybrid Capacitors

Aqueous zinc-ion hybrid capacitors (AZHCs) are considered an encouraging energy storage candidate owing to their promising environmental benignity and electrochemical performance. To give full play to the advantages of AZHCs, vertically aligned reduced graphene oxide/tannic acid (V-rGO/TA) arrays are constructed on the laserpretreated graphite paper (LGP) as flexible carbon-based cathodes (V-rGO/TA/LGP) for AZHCs by a facile laser reduction method. The vertical structure of rGO exhibits abundant physical adsorption sites and ion/electron transfer channels, and the residual oxygen-containing groups of rGO provide favored chemical adsorption sites, which can enhance Zn2+ ion storage. In addition, the TA molecules contribute extra capacity by reversible redox reaction (phenol-quinone transition), further improving the electrochemical performance of the electrode. Consequently, the assembled quasi-solid-state AZHC based on the optimized V-rGO/TA/LGP cathode possesses a high specific capacity of 136.6 mu Ah cm-2 and a maximum energy density of 109.3 mu Wh cm-2. In addition, the device exhibits good flexibility with a capacity retention of 97.0 % even after 3000 bending cycles. This design strategy opens up a new approach to construct a vertically aligned carbon material for achieving highperformance flexible AZHCs and realizing their practical applications.