Nickel(II) Complexes Derived from Schiff Base Ligands Designed as Electrode Materials in Asymmetric Supercapacitor Coin Cells for Enhanced Energy Storage Performance

In this study, three nickel(II)-based Schiff base complexes,
derived
from the condensation of 2-hydroxybenzaldehyde with 2-bromo-4-chloroaniline
(C1), 2-bromo-4-methylaniline (C2), and 2-iodo-4-nitroaniline (C3),
were synthesized using a one-pot in situ reaction strategy without
isolating the corresponding ligands. The complexes were characterized
using standard spectroscopic techniques, and the solid-state structures
for C1 and C2 were determined by a single-crystal X-ray diffraction
analysis. The Schiff base-derived complexes (C1, C2, and C3) were
fabricated as an electrode material, and their electrochemical performance
was evaluated in a 2 M KOH aqueous electrolyte. Cyclic voltammetry
confirmed their pseudocapacitive behavior, as evidenced by distinct
redox peaks. Among the three electrodes, the 2-iodo-4-nitroaniline-based
complex (C3) exhibited a superior charge-storage capability and higher
dielectric polarizability. At 1 A·g–1, the
C3 electrode delivered a maximum specific capacitance of ∼330
F·g–1 and retained ∼92.5% of its capacitance
after 10,000 charge–discharge cycles at 5 A·g–1. An asymmetric (AC//C3) supercapacitor coin cell operating at 1.6
V delivered a specific capacity of ∼98.3 C·g–1 (61.43 F·g–1 or ∼27.3 mAh·g–1) at 0.5 A·g–1. The device
achieved an energy density of ∼21.8 Wh·kg–1 with a power density of ∼378.3 W·kg–1 at 0.5 A·g–1, reaching a maximum power density
of ∼1089 W·kg–1 at 4.0 A·g–1. Furthermore, two coin cells connected in series
produced ∼2.91 V, sufficient to power a red LED, demonstrating
the practical applicability of the C3-based electrode system for real-world
energy storage devices.

本研究中，我们通过一锅原位反应策略合成了三种二价镍基席夫碱（Schiff base）配合物，该类配合物由2-羟基苯甲醛分别与2-溴-4-氯苯胺（C1）、2-溴-4-甲基苯胺（C2）以及2-碘-4-硝基苯胺（C3）缩合得到，且未分离对应的配体。采用标准光谱技术对所得配合物进行表征，并通过单晶X射线衍射分析确定了C1和C2的固态晶体结构。将上述席夫碱衍生配合物（C1、C2、C3）制备为电极材料，并在2 M氢氧化钾（KOH）水溶液电解质中评估了其电化学性能。循环伏安法测试证实了它们的赝电容行为，该结论可通过清晰的氧化还原峰得到佐证。在三种电极中，基于2-碘-4-硝基苯胺的配合物（C3）展现出更优异的储电能力与更高的介电极化率。在1 A·g⁻¹的电流密度下，C3电极的最大比电容约为330 F·g⁻¹，且在5 A·g⁻¹的条件下经过10000次充放电循环后，仍保留约92.5%的初始比电容。一款工作电压为1.6 V的非对称（AC//C3）超级电容器扣式电池，在0.5 A·g⁻¹的电流密度下可实现约98.3 C·g⁻¹的比容量（对应61.43 F·g⁻¹或约27.3 mAh·g⁻¹）。该器件在0.5 A·g⁻¹时的能量密度约为21.8 Wh·kg⁻¹，功率密度约为378.3 W·kg⁻¹；在4.0 A·g⁻¹时可达到约1089 W·kg⁻¹的最大功率密度。此外，两颗串联的扣式电池可输出约2.91 V的电压，足以驱动一枚红色发光二极管（LED），这证明了基于C3的电极系统在实际储能器件中的应用可行性。