Reduced self-discharge of supercapacitors based on surfactant-functionalized NiAl layered double hydroxide

Nickel aluminum layered double hydroxide (NiAl LDH) is an important pseudocapacitive electrode material for its low cost, facile preparation method, and high specific capacity. Due to the lack of chemical stability, however, NiAl LDH-based supercapacitors typically suffer from fast self-discharge. Herein, we report that NiAl LDH functionalized with sodium dodecyl sulfonate (SDS) can show much suppressed self-discharge for supercapacitors assembled from NiAl LDH positive electrodes and activated carbon negative electrodes. Compared to pristine NiAl LDH, the introduction of SDS in NiAl LDH leads to slower decay of open circuit voltage (26.7 vs. 11.6 h for a voltage decay from 1.6 to 0.42 V), reduced leakage current (1.2 vs. 0.17 mA at a charging voltage of 1.6 V), and improved capacitance retention (77 % vs. 49 % after resting for 4 h). The slower self-discharge can be attributed to the negatively charged hydrophobic layer on the surface of SDS-functionalized NiAl LDH particles so that the access of OH− ions to the electrode surface is impeded. As a result, the oxidization of OH− as a main process for the self-discharge of NiAl LDH is largely suppressed.