Keywordsethylene glycol additive aqueous electrolytes, intercalated anodes, oxygen defects, rocking-chair zinc-ion batteries (ZIBs), Zn-(NH 4 ) x WO 3 batteries

The design and synthesis of hollow and porous nanostructured electrode materials is an effective strategy to improve the electrochemical performance of lithium-ion batteries and the hydrogen evolution reaction (HER). Herein, we synthesize hollow and porous Co@Co3O4 nanoparticles embedded in N-doped CNTs (N-CNTs) with rich surface defects through a two-step calcination strategy. The formation mechanism is explored. The influence of oxygen vacancies regulated by the nanoscale Kirkendall effect on the electrochemical performance of the electrode is elucidated. The Co@Co3O4@N-CNTs exhibit remarkable activity for catalyzing the HER with a low onset overpotential of 296 mV (a low Tafel slope of 116.2 mV dec–1), much better than Co3O4@N-CNTs (315 mV for overpotential and 124.2 mV dec–1 for Tafel slope). Significantly, the Co@Co3O4@N-CNTs deliver a high discharge capacity of 990 mA h g–1 after 600 cycles at 0.1 A g–1. Our nanostructure strategy can provide new insights into the strategy for high-rate and highly stable energy storage systems.