Structural Reconstruction Strategy Enables CoFe LDHs for High-Capacity NH₄ ⁺ Storage and Application in High-Energy...

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.