Activation-induced layered structure in NiCoAl by atomic modulation for energy storage application

The surface activation of alloys favors their electrochemical interactions, ion diffusivity, and the rapid kinetics of ions and electrons, leading to the formation of self-supported layered double hydroxides (LDHs) in them. However, the formation of LDHs at different depths in the alloy upon activation, their electronic/atomic structures, and their electrochemical charge storage mechanism, have not been thor-oughly explored. Herein, Ni ion-substituted CoAl alloys are prepared by arc melting and activated by KOH electrolyte, which is responsible for the modulation of the atomic configuration as confirmed by XRD. Raman depth mapping demonstrates how the LDHs vary with depth upon activation and that the octahedral and tetrahedral symmetry sites of CoO and Co3O4 are responsible for the formation of the layered structures of CoOOH and Co(OH)2, respectively. The activated Ni10Co85Al5 has a superior volu-metric capacitance of 4.15 F/cm3 at 0.5 mA/g, which is 38.6 times that of an unactivated one, and excellent cyclic stability up to 5000 cycles, and a voltage of 0.54 V generated from a fabricated super-capacitor cell. X-ray Absorption Spectroscopy (XAS) analysis indicates greater charge transfer by Co than by Ni and the modulation of the local atomic structures facilitates electrochemical charge storage in Ni10Co85Al5. This work presents an easy route for the development of advanced LDHs, and the mecha-nism of electrochemical charge storage in them.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

In this study, Ni ion-substituted CoAl alloys were activated by KOH electrolyte, leading to the formation of self-supported layered double hydroxides (LDHs) and the modulation of atomic structures. Raman depth mapping revealed that the formation of layered structures CoOOH and Co(OH)2 was attributed to the octahedral and tetrahedral symmetry sites of CoO and Co3O4, respectively. The activated Ni10Co85Al5 exhibited superior volumetric capacitance, cyclic stability, and generated a voltage of 0.54 V in a fabricated super-capacitor cell. This work provides an easy route for advanced LDHs development and clarifies the mechanism of electrochemical charge storage in them.