<i>Operando</i> Leaching of Pre-Incorporated Al and Mechanism in Transition Metal Hybrids for Elaborately Enhanced Charge Storage

Abstract

Transition metal based two-dimension (2D) materials with intrinsic/extrinsic pseudocapacitive properties have long attracted tremendous and continous attention for electrochemical energy storage, however the insufficient exposure and utilization of active sites often result in the inferior reactivity, serving as a critical barrier to realize the intrinsic capacitive properties. In response, we for the first time propose a universal ‘nano tailoring’ strategy to in-situ incorporate abundant defects and active sites into low-crystallinity nanosheets enabled by the electrochemically dynamic leaching of Al species. With MnAl layered double hydroxides (LDH) as a representative example, the low-crystallinity potassium-birnessite MnO2 (AK-MnO2) with oxygen vacancies and abundant edge sites is successfully produced after the ‘nano tailoring’ process. Density functional theory calculation reveals that the integrated oxygen vacancies would contribute to the giant optimization of the electron-transfer and ion-adsorption capability. Outstandingly, these integrated microstructure advantages endow the AK-MnO2 hybrids with a high capacitance value of 239 F g-1 at a super-large current density of 100 A g-1. Further combined with the soft XAS (sXAS) results, we unravel that this ‘nano tailoring’ process is significantly determined by the divalent ions involved, more specifically, the reducibility of M2+ in M2+Al-LDH is identified to serve as the key descriptor for the reconstruction rate, which correspondingly is divided into two branches: oxidization-boosting type and non-oxidization type. This ‘nano tailoring’ strategy can provide some important implications and clues to manipulate 2D materials for efficient energy storage and conversion.