Critical roles of molybdate anions in enhancing capacitive and oxygen evolution behaviors of LDH@PANI nanohybrids

Abstract Low-overpotential layered hydroxides (LDHs) with high theoretical capacity are promising electrodes for supercapaterry and oxygen evolution reaction; however, the low electronic conductivity and insufficient active sites of bulk LDHs increase the internal resistance and reduce the capacity and oxygen-production efficiency of electrodes. Herein, we prepared a polyaniline-coated NiCo-layered double hydroxide intercalated with MoO42− (M-LDH@PANI) composite electrode using a two-step method. As the amount of MoO42− in the LDH increases, acicular microspheres steadily evolve into flaky microspheres with a high surface area, providing more active electrochemical sites. Moreover, the amorphous PANI coating of M-LDH boosts the electronic conductivity of the composite electrode. Accordingly, the M-LDH@PANI at an appropriate level of MoO42− exhibits significantly enhanced energy storage and catalytic performance. Experimental analyses and theoretical calculations reveal that a small amount of MoO42− is conducive to the expansion of LDH interlayer spacing, while an excessive amount of MoO42− combines with the H atoms of LDH, thus competing with OH−, resulting in reduced electrochemical performance. Moreover, M-LDH flaky microspheres can efficiently modulate deprotonation energy, greatly accelerating surface redox reactions. This study provides an explanation for an unconventional mechanism, and a method for the modification of LDH-based materials for anion intercalation.