Effects of Carboxyl Functionalized CNT on Electrochemical Behaviour of Polyluminol-CNT Composites

Abstract

The effect of carboxyl groups on the redox activity of polyluminol-carbon nanotube composites was studied. Carboxyl groups were selected due to their known contributions toward surface wettability and pseudocapacitance while often present on naturally derived low-cost porous carbons. Density functional theory (DFT) predicted energetically favoured bonding and a significantly reduced band gap between the luminol and carboxylated graphene relative to that of bare graphene, suggesting improved charge storage for carboxylated carbon substrates. The prediction was validated using bare carbon nanotubes (CNTs) and carboxylated CNTs (COOH-CNTs) as the substrates for in situ chemical polymerized luminol (CpLum). Surface morphological studies showed a ca. 1.1 nm thick coating of CpLum on CNT (CpLum/CNT) and a ca. 1.3 nm on COOH-CNT (CpLum/COOH-CNT), while surface chemical analysis revealed ca. 10% nitrogen from CpLum on both CpLum/CNT and CpLum/COOH-CNT. However, with merely 4.4% of COOH functionalization, CpLum/COOH-CNT was able to store more charge (137.1 ± 17.1 C cm−3) relative to CpLum/CNT (86.1 ± 14.1 C cm−3) and had increased charge retention over 5000 cycles. The insights from these studies can be used to engineer the surface of carbons such as CNTs and ACs to improve the interfacial properties for redox active materials and composites.