Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space

Abstract

Layered double hydroxides (LDHs) are promising supercapacitor materials due to their wide chemical versatility, earth abundant metals and high specific capacitances. Many parameters influencing the supercapacitive performance have been studied such as the chemical composition, the synthetic approaches, and the interlayer anion. However, no systematic studies about the effect of the basal space have been carried out. Here, two-dimensional (2D) CoAl-LDHs were synthesized through anion exchange reactions using surfactant molecules in order to increase the interlayer space (ranging from 7.5 to 32.0 Å). These compounds exhibit similar size and dimensions but different basal space to explore exclusively the interlayer distance influence in the supercapacitive performance. In this line, Co : Al ratios of 2 : 1, 3 : 1 and 4 : 1 were explored. In all cases, an enhancement of the specific capacitance was observed by increasing the basal space, reaching ca. 50 % more than the value obtained from the less-spaced 2 : 1 CoAl-LDH (going from ca. 750 to 1100 F.g−1 at 1 A.g−1). This increment mainly occurs because of the increase in the electrochemical surface area (up to ca. 260 %) and the higher electrolyte diffusion. Interestingly, the best performance is achieved for the lowest Co : Al ratio (i. e. the highest Al content) revealing the important role of the electrochemically inert Al in the structure.