Ligand-Engineered Confined Spaces of Nickel Hydroxide-Organic Frameworks Boost Their Electrochemical Performance in...

Metal hydroxide-organic frameworks (MHOFs) have garnered considerable attention owing to their pillar-tunable structures and superior electrochemical activity, demonstrating significant potential in energy storage and electrocatalysis. However, the stability of the adjacent ligands in alkaline environments and their influence on energy storage behavior remain inadequately understood. In this study, two nickel-based MHOFs, namely NiHOF-BPDC and NiHOF-NDC, have been prepared using electron-withdrawing 4,4'-biphenyldicarboxylic acid (BPDC) and 2,6-naphthalenedicarboxylic acid (NDC) as building linkers. The impact of the ligand chain length on the structural development and electrochemical performance of the materials was comprehensively investigated. The results revealed that the longer BPDC ligand constructs a more open confined space within the layered framework, manifested as enlarged interlayer spacing and increased accessible surface area, thereby significantly enhancing its charge-storage capacity. In contrast, the shorter NDC ligand resulted in a denser stacked framework, which improved the cycling stability. In situ Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses demonstrated that the Ni─O/Ni─OH coordination environment undergoes reversible changes during the electrochemical process, and that the linker-layer created "confined space" is crucial for maintaining the stability and cycling reversibility of the material.