Insight of synergistic effect of different active metal ions in layered double hydroxides on their electrochemical behaviors

Recent years, there have been massive reports of layered double hydroxides (LDHs) used as electrode materials. However, the synergistic effect between different host metal ions on the electrochemical behavior of LDHs is rarely studied. We prepared a series of LDHs with different host metal combinations and investigated their physiochemical properties and redox behaviors to study the synergistic effects between different active metal ions. According to the experimental and theoretical calculation results, LDHs with dual transition metals possessed lower band-gap energies and higher conductivities than mono-transition metal-based samples. The reduced band-gap energy and enhanced conductivity should be ascribed to the hybridization between 3d-orbitals of different transition atoms. As a result, LDHs with dual transition metals exhibited lower charge transfer resistances and redox potentials as well as longer electron lifetime, implying that they could be oxidized or reduced more easily during the redox process. The lowest charge transfer resistance and longest electron lifetime of NiMn-LDHs signify that the synergistic effect between Ni and Mn is the best. From in situ X-ray photoelectron spectroscopy results, more than 50% Ni atoms in NiMn-LDHs can be oxidized under 0.45 V, which also demonstrates the excellent redox efficiency of NiMn-LDHs. (C) 2017 Elsevier Ltd. All rights reserved.