Dynamic Morphological Evolution of Co-Based Layered Double Hydroxide Nanosheets Investigated by In Situ Electrochemical-Atomic Force Microscopy

With excellent electrochemical activity, low consumption, and easy synthesis, Co-based layered double hydroxides (LDHs) have been applied to electrochemical energy conversion and storage devices. Understanding the mechanisms of morphological evolution and capacity changes under potential cycles is critical for the design of high-performance materials of Co-based LDHs. Here, we monitored the morphological evolution of two kinds of CoFe-LDH nanosheets and four kinds of CoAl-LDH nanosheets using in situ electrochemical-atomic force microscopy. The CoFe-LDH nanosheets present the growth of granular particles and the deterioration of capacity performances, which might be due to the irreversible conversion of hydroxide into oxyhydroxide under potential cycles. The CoAl-LDH nanosheets maintain more capacity and do not form granular particles under potential cycles, resulting from the electrochemical reaction reversibility of Co2+ and the stability of the host hydroxide layer enhanced by Al3+. The introduction of Al3+ into the Co-based LDH structure is conducive to cyclic stability of capacity compared to that of Fe3+. Additionally, the CoAl-LDH nanosheets with different Co/Al molar ratios present varying degrees of dissolution and variations of capacity under potential cycles. A moderate Co/Al molar ratio of CoAl-LDH nanosheets is beneficial to cyclic stability. These findings would provide a deep insight into the mechanisms of capacity changes based on in situ morphological evolution and support for the optimization of such material performance.