MXene interlayer space expansion: Alleviating coulomb attraction and steric resistance on multivalent charge carriers toward micro-supercapacitors with enhanced areal energy density

Abstract

Sluggish bivalent Mg 2+ diffusion between MXene interlayers arising from narrow physical space and strong electrostatic attraction is significantly facilitated by interlayer expansion via the insertion of bacterial cellulose nanospacer, endowing the further fabricated symmetric Mg-ions aqueous micro-supercapacitors with enhanced areal energy density. • Mg 2+ diffusion between MXene interlayers is facilitated by interlayer expansion engineering. • An areal energy density up to 32 μWh cm -2 is realized on the fabricated symmetric Mg 2+ micro-supercapacitor. • A stretchable SMI-MSC array with stable output voltage under elongation up to 200% is fabricated. Sluggish multivalent charge carriers diffusion between MXene interlayers arising from narrow physical space and strong electrostatic attraction has long been a challenge in promoting the areal energy densities of MXene-based aqueous micro-supercapacitors (MSCs). Herein, a simple interlayer space expansion strategy of MXene-based self-assembled film electrode is proposed to alleviate coulomb attraction and steric resistance on divalent Mg 2+ transfer toward symmetric Mg-ions aqueous micro-supercapacitors (SMI-MSCs) with significantly enhanced areal energy density. The electrochemical tests prove that the enlarged interlayer space by introducing 1D bacterial cellulose (BC) nanospacer between Ti 3 C 2 T x flakes can effectively reduce the diffusion barrier of Mg 2+ within the obtained Ti 3 C 2 T x /BC composite film electrode. Benefiting from the simultaneously repressed kinetics of hydrogen/oxygen evolution on the Ti 3 C 2 T x /BC composite film electrode rooting in the employed neutral polyacrylamide/Mg(CF 3 SO 3 ) 2 hydrogel electrolyte, the as-fabricated SMI-MSCs acquire a high areal energy density of 32 μWh cm −2 and a cell voltage up to 1.2 V. Encouraged by the superior energy efficiency of single SMI-MSC unit, a stretchable SMI-MSC array has further been fabricated via integrating the SMI-MSCs on flexible circuit board with bridge-island architecture. The obtained SMI-MSC array can provide stable and adjustable output of voltage and energy under elongation up to 200%, revealing great application potential for wearable/flexible power source.