The development of high-performance supercapacitors is critical to meet the growing demand for efficient energy storage systems. This study presents a novel electrochemical anion-exchange method to synthesize porous Ni/Co hydroxide nanosheets with exceptional electrochemical properties. By applying an electric field during alkaline hydrolysis of Ni0.7Co0.3-MOF nanosheets, we achieved controlled transformation into hierarchical Ni0.7Co0.3(OH)2 nanosheets with enhanced porosity and structural integrity. The electrochemical anion exchange process not only accelerates nucleation but also directs the migration of charged species, leading to the formation of abundant ion channels and improved charge transfer kinetics. The optimized sample, designated as Ni0.7Co0.3(OH)2-1000c after 1,000 CV cycles, exhibits a remarkable specific capacitance of 2115 C g⁻¹ (4230 F g⁻¹) in a three-electrode system. When integrated into a hybrid supercapacitor using N/O co-doped porous carbon (NOPC) as the negative electrode, the device delivers a high energy density of 74.7 Wh kg⁻¹ and a power density of 5,990.6 W kg⁻¹. Remarkably, it maintains 74.6% of its initial capacitance after 8,000 charge-discharge cycles at 5 A g⁻¹, demonstrating outstanding cycling stability. The superior performance is attributed to the well-developed porous architecture, rich surface area, and efficient ion/electron transport enabled by the electric-field-assisted synthesis. This strategy offers a low-cost, scalable approach to fabricate deep-discharge electrodes without relying on high-temperature calcination. Moreover, it enables the recovery and reuse of organic ligands from MOFs, enhancing sustainability. The findings provide a new paradigm for designing advanced nanomaterials from MOF precursors, with broad implications for next-generation energy storage devices.
Microstructural Evolution and Mechanism of Electric-Field-Assisted Hydrolysis
The morphological evolution of Ni0.7Co0.3-MOF during electrochemical anion exchange reveals a unique transformation pathway. Initially, the MOF nanosheets exhibit a compact, layered structure with minimal porosity. Upon application of cyclic voltammetry in 6 M KOH solution, OH⁻ ions begin to attack the metal-ligand bonds, initiating hydrolysis. At early stages (250 cycles), the electric field promotes localized charging and discharging, resulting in layer stacking due to accumulated electrostatic forces. As the number of cycles increases to 500, the accelerated nucleation rate leads to the growth of hydroxide domains on the surface, forming ordered hierarchical structures. At 1,000 cycles, the combined effect of electric field-driven ion migration and continuous hydrolysis causes directional breakdown of the nanosheet framework, generating extensive mesopores throughout the material. High-resolution TEM confirms the presence of lattice fringes corresponding to (100) and (101) planes of Ni(OH)₂ and Co(OH)₂, indicating crystalline phase formation. Selected area electron diffraction (SAED) patterns show polycrystalline rings consistent with both Ni(OH)₂ and Co(OH)₂ phases. Elemental mapping further verifies uniform distribution of Ni, Co, and O across the nanosheets. Notably, the BET surface area of Ni0.7Co0.3(OH)2-1000c reaches 78.5 m² g⁻¹—significantly higher than that of the original MOF (219.6 m² g⁻¹) and the conventionally hydrolyzed product (154.3 m² g⁻¹)—due to the removal of organic linkers and creation of internal pores. This microstructural refinement enhances electrolyte accessibility and active site exposure, directly contributing to the ultrahigh capacitance observed.
Enhanced Electrochemical Performance and Charge Storage Mechanism
The electrochemical behavior of Ni0.7Co0.3(OH)2-xc materials was systematically evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectroscopy. CV curves reveal distinct redox peaks associated with the reversible conversion of Co(OH)₂ ↔ CoOOH and Ni(OH)₂ ↔ NiOOH, confirming Faradaic charge storage mechanisms. Among all samples, Ni0.7Co0.3(OH)2-1000c shows the largest integrated area under CV curves, indicating superior capacitive performance. GCD measurements confirm a specific capacitance of 2115 C g⁻¹ at 1 A g⁻¹, which remains stable even at high current densities. Rate capability analysis shows that Ni0.7Co0.3(OH)2-1000c retains 58.1% of its capacity at 10 A g⁻¹, outperforming other variants. Kinetic analysis based on power-law fitting indicates that the charge storage process is predominantly diffusion-controlled (b ≈ 0.61), suggesting effective ion intercalation within the layered structure. Quantitative decomposition of capacitive and diffusion contributions reveals that 63.0% of the total capacitance in Ni0.7Co0.3(OH)2-h arises from surface processes, whereas only 36.4% in Ni0.7Co0.3(OH)2-1000c comes from such mechanisms—indicating greater involvement of bulk diffusion. This shift reflects deeper ion penetration enabled by the engineered porous network. EIS results further demonstrate lower charge transfer resistance (Rct = 0.26 Ω cm²) and ionic resistance (Rs = 0.93 Ω cm²), confirming faster reaction kinetics. These findings collectively highlight the effectiveness of electric-field-assisted hydrolysis in optimizing both surface and bulk electrochemical activity.
Hybrid Supercapacitor Device Integration and Practical Application
To assess real-world applicability, a hybrid supercapacitor was fabricated using Ni0.HSP90B Antibody In Vivo 7Co0.Leukotriene B4 Receptor Antibody In Vivo 3(OH)2-1000c as the positive electrode and NOPC as the negative electrode, operating in a 3 M KOH aqueous electrolyte.PMID:35184042 The device demonstrates a wide operational voltage window of up to 1.7 V, confirmed by the absence of hydrogen and oxygen evolution reactions at high potentials. CV curves remain symmetric across scan rates from 5 to 50 mV s⁻¹, indicating excellent rate capability. GCD tests at various current densities (1–10 A g⁻¹) show nearly equal charge and discharge times, reflecting near-100% coulombic efficiency. The Ragone plot illustrates a maximum energy density of 74.7 Wh kg⁻¹ at 838.9 W kg⁻¹, maintaining 14.9 Wh kg⁻¹ even at 5,990.6 W kg⁻¹. After 8,000 cycles at 5 A g⁻¹, the device retains 74.6% of its initial capacitance, with a coulombic efficiency of 94.0%, underscoring long-term reliability. Structural stability is further validated via post-cycling SEM images, showing intact nanosheet morphology for Ni0.7Co0.3(OH)2-1000c, unlike the partial agglomeration observed in pristine MOF samples. Furthermore, the assembled device successfully powers green LED bulbs, demonstrating practical energy delivery potential. This work establishes a robust platform for developing high-energy, high-power, and durable supercapacitors suitable for portable electronics and renewable energy integration.
Innovative Strategy for Sustainable and Scalable Electrode Fabrication
This study introduces a transformative approach to synthesizing high-performance supercapacitor electrodes through electric-field-assisted anion exchange of MOFs. Unlike conventional thermal pyrolysis methods that require high temperatures and lead to uncontrolled particle growth and ligand degradation, this electrochemical method operates under mild conditions while enabling precise control over nanostructure evolution. The ability to recycle and reuse organic ligands enhances the environmental and economic sustainability of the process. The use of Ni foam as a conductive substrate allows direct growth of active materials, eliminating the need for binders and improving electrical contact. The strategy is adaptable to various MOF compositions, opening avenues for tuning composition, porosity, and functionality. The resulting Ni/Co hydroxide nanosheets combine high surface area, hierarchical porosity, and excellent conductivity, making them ideal candidates for deep-discharge applications. The success of this method highlights the importance of external fields in guiding chemical transformations at the nanoscale. It paves the way for future innovations in functional nanomaterial design, particularly for energy storage and conversion technologies. This work not only advances fundamental understanding of MOF-to-hydroxide conversion but also provides a practical, scalable route toward next-generation supercapacitors with unprecedented performance metrics.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
