Functionalization and metal doping of MWCNTs for hydrogen storage

Abstract

This study aims to contribute to sustainable energy solutions, particularly by emphasizing the importance of the transition to hydrogen energy. Multi walled carbon nanotubes (MWCNTs) are among the promising materials for hydrogen storage. However, their storage capacity is currently low. One way to increase is to functionalize MWCNTs and create their metal doped products. In this study, MWCNT was first functionalized, then Schiff bases with different aldehyde derivatives were synthesized, and the produced Schiff bases were doped with cobalt and nickel. After the samples were characterized by Fourier transform infrared spectroscopy (FTIR), Raman, Brunner-Emmett-Teller (BET), differential thermal analysis/thermogravimetry (DTA/TG), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometer (ICP-OES) and electrochemical impedance spectroscopy (EIS), their hydrogen storage capacities were measured as a function of pressure at cryogenic temperature. FTIR analysis confirmed the hydroxylation, amination and Schiff base formation of MWCNT. DTA/TG thermograms showed that the produced samples degraded in different and more steps than MWCNT. SEM/EDX proved that the morphology of MWCNT changed with functionalization and cobalt and nickel entered the structure by doping. With functionalization, the BET surface area of MWCNT decreased. All samples did not have micropores but largely had mesopores. The hydrogen storage capacities of the samples increased with increasing pressure, reaching a maximum and then decreasing due to excessive adsorption. Compared to MWCNT, MWCNT-OH has 73 % and MWCNT-O-TMSPEDA-AP-Co has 95 % more hydrogen storage capacity. The results show that MWCNT modification and cobalt doping are an effective method to achieve high capacities. The hydrogen storage capacity of the produced samples is similar to the values in the literature and even higher than some of them.