Sodium‐ion hybrid capacitors (SICs), combining the advantages of both sodium‐ion batteries (SIBs) and electrochemical supercapacitors, have captured sustained attention in the field of energy storage devices due to their high energy and power density, long lifespan, and excellent operation stability. However, conventional SICs based on battery‐type anodes and capacitive‐type cathodes suffer from imbalance on capacity and kinetics. In this regard, rational structure design on electrode materials is still necessary for SICs. Over the past two decades, tremendous efforts have been devoted to the exploration of suitable electrode materials to fabricate high‐performance SICs. Herein, after a brief introduction on the charge storage mechanisms of SICs, the recent developments on electrode materials for SICs are summarized, especially focusing on material design strategies as well as the relationship between structure and corresponding electrochemical performances. Furthermore, the challenges and opportunities for the further development of SICs are also proposed.

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Understanding the basic physicochemical properties of gas molecules confined within nanobubbles is of fundamental importance for chemical and biological processes. Here, we successfully monitored the nanobubble-confined electrochemical behaviors of single platinum nanoparticles (PtNPs) at a carbon fiber ultramicroelectrode in HClO 4 and H 2 O 2 solution. Due to the catalytic decomposition of H 2 O 2 , a single oxygen nanobubble was formed on individual PtNPs to block the active surface of particles for proton reduction and to suppress their stochastic motion, resulting in significantly distinguished current traces. Furthermore, the combination of theoretical calculations and highresolution electrochemical measurements allowed the nanobubble size and the oxygen gas density inside a single nanobubble to be quantified. Moreover, the ultrahigh oxygen density inside (1046 kg/m 3 ) was revealed, indicating that gas molecules in a nanosized space existed with a high state of aggregation. Our approach sheds light on the gas aggregation behaviors of nanoscale bubbles using single-entity electrochemical measurements.

No abstract

Understanding the basic physicochemical properties of gas molecules confined within nanobubbles is of fundamental importance for chemical and biological process. Here we successfully monitored the nanobubble-confined electrochemical behaviors of single platinum nanoparticles (PtNPs) at a carbon fiber ultramicroelectrode in HClO4 and H2O2 solution. Owing to the catalytic decomposition of H2O2, a single oxygen nanobubble formed on individual PtNPs to block the active surface of particle for proton reduction and suppress their stochastic motion, resulting in significantly distinguished current traces. Furthermore, the combination of theoretical calculation and high-resolution electrochemical measurement allowed the size of nanobubble and the oxygen gas density inside a single nanobubble to be quantified. And the ultrahigh oxygen density inside (9286 kg/m3) was revealed, indicating gas molecules in a nanosized space existed with a high state of aggregation. Our approach sheds light on gas aggregation behaviors of nanoscale bubbles using single-entity electrochemical measurement.