A Pd nanocatalyst supported on multifaceted mesoporous silica with enhanced activity and stability for glycerol electrooxidation

Abstract

Glycerol is massively produced as a byproduct of biodiesel manufacturing, which decreases its price and increases its inadequate disposal. The use of glycerol to feed anodes of alkaline fuel cells and electrolysers has emerged as potential alternatives for its use. However, the activity and stability of commercial Pd/C nanoparticles currently proposed do not reach the required performance. Here, we propose a new Pd catalyst deposited in mesoporous silica (SiO₂) with enhanced activity and stability for glycerol electrooxidation in alkaline media. We synthesized well-ordered mesoporous silica with pores in the form of a fountain pen and lmm symmetry, in a cage-like arrangement. Such a structure was proved by experiments of microscopy, X-ray diffraction, N₂ isotherms and small-angle X-ray scattering measured in synchrotron light. Next, we produced patterned Pd/SiO₂ in a one-step synthesis and ordered Pd after template removal. The Pd catalysts were characterized by microscopy, dispersive X-ray spectrometry and X-ray diffraction. Pd/SiO₂ and Pd showed improved current density and stability compared to Pd/C. The current density of Pd/SiO₂ reached twice the values found for Pd/C. The enhancement is understood as a multiple role of the mesoporous silica support, which works as a seed mediator to order the Pd nanoparticles and mainly as a trap that confines the reactant inside the mesoporous structure, increasing the frequency of collision with active Pd sites. Furthermore, we showed that no carbonyl or intact glycerol was found on Pd/SiO₂ after exhaustive cycles of use, except for adsorbed CO that was quickly removed from the surface, which is a probable reason for an improved pathway of glycerol electrooxidation via CO.