Pillar-Coordinated Strategy to Modulate Phase Transfer of α-Ni(OH)₂ for Enhanced Supercapacitor Application

Modulating the phase property of electrode materials is of intrinsic importance for enhanced energy storage performance. Here, through a pillar-coordinated strategy, a series of metaborate pillar-coordinated hierarchical α-Ni(OH)2 (Ni(BO2–)-LDH) are fabricated via Ni-MOF precursor etching process. During the etching process, the coordinated organic ligand is gradually substituted by inorganic anions (OH– and BO2–) with small size and the BO2– anions are effectively coordinated on the surface of as-formed α-Ni(OH)2 layer to fabricate a pillar-coordinated α-Ni(OH)2 structure. The physical morphology of MOFs parent is successfully maintained, which provides rich pores and channels for fast diffusion of electrolyte. Meanwhile, the unique pillar-supported α-Ni(OH)2 structure is robust to avoid the phase-transfer reaction from the α-phase to β-phase during the charge/discharge process in strong alkaline electrolyte, which can provide a deep and durable Faraday reaction. Therefore, the optimized Ni(BO2–)-LDH-4 shows a capacity value of 244.4 mAh g–1 (1760 F g–1) at 1 A g–1 and an outstanding cycle performance of keeping approximately 82.1% of its initial capacitance after 10 000 cycles at 5 A g–1. Furthermore, a hybrid supercapacitor with the Ni(BO2–)-LDH-4 and three-dimensional reduced graphene oxide (3D-RGO) as electrodes presents a high energy density of 56.5 W h kg–1 at 0.111 kW kg–1.