Structural Reconstruction Strategy Enables CoFe LDHs for High‐Capacity NH4+ Storage and Application in High‐Energy Density Ammonium‐Ion Hybrid Supercapacitors**

Exploration of high-performance aqueous ammonium-ions hybrid supercapacitor has attracted tremendous research attention recently. Herein, structural reconstructed cobalt-iron layered double hydroxides (SR-CoFe LDHs) featuring copious structure defects (i. e., oxygen-vacancies, M-O bonds, MOO- bonds, coexistence of Co2+ /Co3+ and Fe2+ /Fe3+ ) are reported as a high-capacity cathode for NH4+ storage. The resulting SR-CoFe LDHs can deliver a reversible capacity of 167.9 mAh g-1 at 0.5 A g-1 , which is 3.3 folds higher than that of pristine CoFe-LDHs. Ex-situ experimental results and theoretical studies denote that the presence of structural defects in the CoFe-LDHs can lower the NH4+ adsorption energy and induced electron delocalization to enhance the electrical conductivity, rendering the CoFe-LDHs exhibits excellent performance for NH4+ storage. As a proof of concept, ammonium-ion hybrid supercapacitor has been assembled with CoFe-LDHs as the cathode and hierarchical carbon as the anode, which can deliver a large specific capacitance of 238.3 F g-1 , long cycle stability over 10000 cycles, and high energy density of 66.2 Wh kg-1 within a wide working voltage of 2 V. Overall, this work offers some insights into the design of high capacity cathode for aqueous NH4+ storage and also illustrates the construction of aqueous hybrid devices with NH4+ as the charge carrier.