Carbon‐Nanotubes@MnO2‐Nanosheets Core‐Shell Arrays on Carbon Cloth for High‐Performance Flexible Supercapacitor and Capacitive Deionization

Rational electrode structure design is a key to bridging electrochemical energy storage and capacitive deionization devices. However, electrode materials are often limited by sluggish ion transport, low utilization of electroactive sites, and unstable integration between redox‐active phases and conductive frameworks. Here, we developed a proton‐coupled self‐templating hollowing‐growth strategy to construct hierarchical core‐shell arrays of hollow carbon nanotubes (CNTs) and conformal MnO2 nanosheets (CMT). Proton‐induced etching of zinc oxide (ZnO) nanowires was coupled with concurrent deposition of redox‐active MnO2, yielding a hierarchical hollow architecture with conductive carbon backbones, hollow ion‐transport conduits, and accessible MnO2 nanosheets. This integrated structure accelerates charge transfer, facilitates electrolyte penetration, and improves electroactive site utilization. As a result, the optimized CMT‐40 electrode delivers an areal capacitance of 0.52 F cm−2 at 2 mV s−1 and retains 0.25 F cm−2 at 100 mV s−1. When assembled into a flexible asymmetric supercapacitor, the device delivered a maximum volumetric energy density of 2.85 mWh cm−3 at 25.5 mW cm−3 and retained ~1.8 mWh cm−3 at a high power density of 453.8 mW cm−3. In capacitive deionization (CDI), the same architecture enables fast ion electrosorption and a salt adsorption capacity of 132.2 mg g−1 at 1000 ppm sodium chloride (NaCl) solution, together with good cycling stability. This work provides an effective framework for designing multifunctional hollow electrodes for integrated high‐rate energy storage and electrochemical desalination. A proton‐coupled, self‐templating hollowing–growth strategy is developed to fabricate hierarchical carbon@MnO2 core–shell electrodes, consisting of hollow carbon nanotube arrays conformally coated with ultrathin MnO2 nanosheets. This architecture enables rapid charge and ion transport while maximizing the utilization of electroactive sites, delivering high performance in both flexible supercapacitors and capacitive deionization applications.