Synthesis and electrochemical characterization (HER-NER) of platinum-based materials supported in a carbon nano-tube matrix

Nano-particles of platinum were prepared using Metal Organic Chemical Vapor Deposition (MOCVD) technique and supported in a carbon nano-tube (CNT) matrix in order to obtain different atomic relationship: Pt (1%)/CNT, Pt (5%)/CNT and Pt (15%)/CNT. The as-prepared Pt/CNT was deposited on a glassy carbon (GC) electrode. Nitrate electro-reduction reaction (NER) was used as a probe to evaluate their catalytic activity. According to XRD analysis the particle size was determined as 15, 13 and 12 nm for Pt (15%)/CNT, Pt (5%)/CNT and Pt (1%)/CNT, respectively. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) confirmed the presence of nano-tubes and the platinum atomic ratio in each sample. The adsorption-desorption region related to the Hydrogen Evolution Reaction (HER) was evaluated. The charge obtained (Q/μC) followed the order Pt(15%)/CNT>Pt(5%)/CNT>Pt(1%)/CNT, in agreement with platinum content. The i-E profiles at nitrate-containing solutions showed a redox process corresponding to the NO₃ ^-reduction. Cyclic voltammetry (CV) coupled with rotating disk electrode (RDE) technique revealed that the NER is affected by the rotation rate, an indication of a strong competition of nitrate ion and protons at the electrode interface. Studies as a function of NO₃^- concentration (0.001, 0.01, 0.1 and 1.0M) were also carried out. The electrical current attributed to nitrate reduction increased, for all samples, as a function of concentration. Nevertheless, this current magnitude is not severely affected by the content of platinum-nanoparticles. These results have been discussed in terms of local disorders due to particles size-distribution as well as the support matrix geometry (SMG).