Electrochemical Sacrificial Alchemy: Crafting Hollow Hydroxide Hierarchy for Practical Aqueous Energy Storage Solution

Abstract Effective utilization of internal active sites in high‐mass loading electrode materials is essential for advancing practical energy storage. Herein, a novel electrochemical sacrificial alchemy for the first time to directly transform the solid Co‐Ni‐Zn carbonate hydroxide (CH) into its hollow structure with a strategic hierarchical architecture is introduced. In contrast to the complex and often cumbersome procedures of traditional methods, the approach is built on the simple electrochemically induced in situ etching and remodeling process. The experimental and theoretical analyses highlight the significant role of electric field force‐induced Zn sacrificial etching and hydroxide redeposition in creating internal cavities and regenerating external active sites, leading to the final hollow hierarchical structure with primary 1D hollow nanorod arrays and secondary reconstructed 2D nanoflakes, effectively exposing abundant energy storage sites. Benefiting from the synergistic effect, the resulting Co‐Ni‐Zn CH exhibited exceptional electrochemical performance. As proof of concept, a modular pouch‐type hybrid supercapacitor (HSC) composed of Co‐Ni‐Zn CH cathode achieved an ultrahigh energy density of 46.9 Wh kg −1 . This device can efficiently power consumer electronics with a faster charging speed compared to commercial shared power banks. This research unveils a facile electrochemical approach for structuring electrode materials in energy storage solutions.