Laser Unzipped Single Wall Carbon Nanotube Coating on Copper as Effective Bifunctional Electrocatalyst: An Experimental and DFT Study

Abstract

CO2 laser-assisted functional unzipping of single wall carbon nanotube (SWCNT) coating on copper is investigated as an energy-economic, non-chemical, direct-write dry process. The laser irradiation at an optimized power and scan speed is shown to partially unzip the SWCNTs and lead to a novel microgradient-patterned planar 1D-2D heterostructure. The in-process nitrogen doping can also be accomplished with urea incorporation during laser unzipping, rendering interesting morphological forms such as twists and folds. Moreover, density functional theory (DFT) studies are performed to elucidate the electronic structure of the pristine, nitrogen-doped SWCNTs and the possible unzipping process. The studies reveal that nitrogen dopant sites in the chiral SWCNTs serve as weak centres in the nanotube, triggering coordinated and controlled unzipping. It is further shown that concurrent in-process nitrogen doping and unzipping can yield an efficient “bifunctional” catalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), supported by electron density differences obtained using DFT. The optimized catalyst rendered an ORR half-wave potential of 0.71 V (versus RHE) and an OER overpotential of 410 mV at 10 mA cm−2 with excellent catalytic stability. The preliminary study of the stated electrocatalytic properties for Zn-air battery application is also reported.