Effect of activation/purification of multiwalled carbon nanotubes (MWCNTs) on the activity of non-platinum based hypo-hyper d-electrocatalysts for hydrogen evolution

Commercial multiwalled carbon nanotubes (MWCNTs) were used as a catalyst support for non-platinum hypo-hyper d-electrocatalysts. In order to improve the performance of these catalysts, activation/purification of MWCNTs in acid medium (HNO₃) was carried out. The physical and surface changes of MWCNTs were investigated by DTA/TGA analysis, Raman spectroscopy, and cyclic voltammetry. Structural changes of the electrocatalysts were observed by infrared spectroscopy and SEM. Their use as a support for electrocatalysts for hydrogen evolution was demonstrated, and shown to be more suitable compared to the traditional carbon support material − carbon black (Vulcan XC-72). The electrocatalysts consisted of 10% Co + 18% TiO₂ + MWCNTs. Activation/purification removes the amorphous carbon phase in the MWCNTs. As a result of both shortening and opening of carbon nanotubes, better dispersion of metallic particles (the active catalytic centers) was achieved. Thus, trans-particle and inter-particle porosity of the electrocatalytic material was improved, implying increase of catalytic activity for hydrogen evolution.