Structural Reconstruction Strategy Enables CoFe LDHs for High‐Capacity NH<sub>4</sub><sup>+</sup> Storage and Application in High‐Energy Density Ammonium‐Ion Hybrid Supercapacitors**
Dewei Wang, Jiaqi Sun, Long Chen
Abstract
Abstract 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 Co 2+ /Co 3+ and Fe 2+ /Fe 3+ ) are reported as a high‐capacity cathode for NH 4 + 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 NH 4 + adsorption energy and induced electron delocalization to enhance the electrical conductivity, rendering the CoFe‐LDHs exhibits excellent performance for NH 4 + 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 NH 4 + storage and also illustrates the construction of aqueous hybrid devices with NH 4 + as the charge carrier.