From 1D to 2D: Controllable Preparation of 2D Ni-MOFs for Supercapacitors

Tailoring Electrocatalytic Ov-NiOOH by Regulating the Reconstruction in Ni-Based Metal-Organic Frameworks with Highly Asymmetric Ni-O Coordination

Metal-organic frameworks have aroused growing interest in the research of energy conversion and storage. However, their specific configuration, especially the coordination environment of metal active sites, has not been well designed. Their role in regulating the structural reconstruction of pre-electrocatalysts remains ambiguous. Herein, this work reports a dual-ligand strategy to design a Ni-MOF with asymmetric Ni-O coordination, named Ni-BDC-DOBDC, which occupies unsaturated Ni sites and strengthens Ni-O bonds. As inspected by X-ray absorption near edge structure as well as a series of in situ and ex situ characterizations, this special Ni-O coordination contributes to Ov-NiOOH with rich oxygen vacancies during fast self-reconstruction at a lower potential. Moreover, theoretical results reveal that Ni sites in Ov-NiOOH occupy a higher d-band center, a lower adsorption energy barrier, and a more electronic negative surface in the oxygen evolution reaction, leading to good electrocatalytic performance. Overall, Ni-BDC-DOBDC catalysts exhibit a low overpotential of 202 mV at 10 mA cm-2 and outstanding stability within 240 h. The insights in this work pave the way for high-performance MOF-based catalysts by regulating their self-reconstruction kinetics through a new aspect of asymmetric ligand engineering.

MOF-Derived Zn/N-Doped Porous Carbon Film on a Carbon Nanotube for High-Performance Supercapacitors

Designing high-performance binder-free electrochemical electrodes is crucially important toward supercapacitors. In this paper, a Zn/N-doped porous carbon film coating on flexible carbon nanotubes (ZIF-8@CT-800) derived from the epitaxial Zn-MOF film growth on cotton textile was successfully fabricated via a combination of the liquid-phase epitaxial (LPE) method and calcination treatments. The ZIF-8@CT-800 serves directly as a self-supported electrode for supercapacitors and exhibits a high areal capacitance of 930 mF·cm-2 at a current density of 1 mA·cm-2 and a good recyclability of 86% after 2000 cycles. The excellent supercapacitor property is ascribed to the unique structural design of ZIF-8@CT-800, which provides appropriate channels for enhanced electronic and ionic transport as well as increased surface area for accessing more electrolyte ions. This work will provide significant guidance for designing MOF-derived porous carbon to construct flexible binder-free electrode materials with high electrochemical performance.

Rational Design of NiCo-borate/GO Heterojunction as a High-Performance Supercapacitor Electrode

The bottleneck in the preparation of supercapacitors is how to develop high-energy and high-power-density devices by using appropriate materials. Herein, a novel NixCo3-x-B/GO heterostructure material was synthesized through a simple ultrasonic and precipitation method. The prepared NixCo3-x-B/GO heterostructure exhibits significant improvements in supercapacitor performance than NixCo3-x-B. The presence of GO effectively suppresses the excessive growth and accumulation of NixCo3-x-B; therefore, Ni2.7Co0.3-B/GO exhibits the best performance as an electrode material for supercapacitors: a high specific capacitance (Cm, 1789.72 F g-1@1 A g-1) and excellent rate performance. The asymmetric supercapacitor (ASC) device of Ni2.7Co0.3-B/GO//AC exhibits a Cm of 76.6 F g-1@1 A g-1, a large voltage window of 1.6 V, and a high energy density (ED) of 98.0 Wh kg-1. Furthermore, a flexible, all-solid-state supercapacitor assembled with Ni2.7Co0.3-B/GO as both the positive and negative electrodes demonstrates a Cm of 46.9 F g-1@1 A g-1. Even after multiple folding and bending at various angles, the device maintains excellent performance, showcasing remarkable stability. With a power density (PD) of 479.7 W kg-1, the device achieves a high ED of 60.0 Wh kg-1. This work provides valuable insights into the synergistic effects in electrochemical processes based on heterostructure materials.