Accelerated ion transport and charging dynamics in more ionophobic sub-nanometer channels

Abstract

Layered two-dimensional (2D) nanomaterials are highly promising for boosting energy density of supercapacitors for industrial translation, however their rate performances are limited by the intrinsically sluggish ion transport within sub-nanochannels. Herein, we elaborate and prove a novel concept of electrostatic-repulsion-enabled ionophobic and hydrogen-bonding-enabled hydrophilic surface to substantially enhance ion transport and charging dynamics in sub-nanochannels. The concept is experimentally and theoretically developed through constructing less negatively-charged (-OH terminated) MXene nanochannels and molecular dynamics (MD) studies of electrolyte dynamics in MXene nanochannels with different functional groups, revealing that -OH terminations enable hydrophilic but ionophobic features for unimpeded ion transport. The ion transport mechanisms during the negative charge are further revealed by electrochemical quartz crystal microbalance tests. Electrochemical measurements demonstrate that hydrophilic but ionophobic sub-nanochannels feature drastically reduced ion diffusion resistance (by 90%) and significantly-improved rate performance (from 20.4% to 78.4% at 50 A g–1). The universality of this sub-nanochannel engineering concept is validated in acid electrolyte and composite materials, making it potentially applicable across diverse areas of nanoscience and nanotechnology.