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

NH₄ ⁺ storage: Structural reconstructed cobalt-iron layered double hydroxides featuring copious structure defects are reported as a high-capacity cathode for NH₄ ⁺ storage. The resulting sample can not only deliver a large reversible capacity but also act as the cathode for construction of ammonium-ion hybrid supercapacitors.

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 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.

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