Multi-TpyCo2+-based conductive supramolecular hydrogels constructed by “bridge bonds” for rechargeable Zn-air batteries with ultrastable cycling stability over 1100 h

Abstract

For supramolecular hydrogels, a deep understanding of the gelation process and exploration of their application in rechargeable electrochemical batteries remain a significant challenge. Herein, this paper demonstrates a series of novel multi-TpyCo²⁺-based low-molecular-weight supramolecular hydrogelators and further discovers the spontaneous gelation mechanism by experimental and calculation results. The hydrogen bond and π–π conjugation have a synergistic driving effect in gelation. In particular, the hydrogen bond between the free Cl anion and H₂O molecules serves as a “bridge bond” to connect nearby structural units, contributing to forming a stronger network structure. Owing to the difference of the spatial confinement effect of the gelator, gelled (Tpy)_xCo_x displays a conductivity-dependent activity for the oxygen evolution reaction, and (Tpy)₄Co₄ presents the lowest overpotential of 264 and 301 mV at 10 and 100 mA cm⁻², respectively. More importantly, with (Tpy)₄Co₄ as the air cathode, liquid rechargeable Zn-air batteries exhibit an ultrastable cycling stability of more than 1100 h (5500 cycles @2 mA cm⁻²) and a high energy efficiency of 65.3% with negligible performance decay. Moreover, the fabricated (Tpy)₄Co₄-based quasi-solid-state battery displays a superior stability of 270 h (1 mA cm⁻² at 25 °C) and 25 h (0.5 mA cm⁻² at −40 °C).