Design functional catalytic materials from first-principles methods for methanol fuel cells

Abstract

Direct methanol fuel cells (DMFCs) offer ample opportunities for high-efficiency and sustainable power generation. However, the lack of cost-efficient electrocatalysts for the kinetically sluggish cathodic oxygen reduction reaction (ORR) hinders the technology advancement. The solutions to solve these fundamental challenges would benefit from unique insights from molecular-level modeling. The first focus of this thesis aims to construct representative molecular models for a vertically aligned carbon nanofiber (VACNF) architecture as a functional support for the platinum-based ORR catalysts. Density Functional Theory (DFT) combined with classic molecular dynamics was employed to produce two supported composite catalyst nanostructures. Both models revealed the mechanistic and catalytic origins corroborating the observed linear sweeping voltammetry. The Pt nanoparticles supported on VACNF show preferential binding at their exposed low coordinated sites, resulting in a lower ORR limiting potential than on Pt (111) facet. This thesis also explored ORR electrocatalysts consisting of non-platinum group metals (Fe, Co, Ni), atomically dispersed and embedded in 2D materials. The active centers are stable in alkaline ORR conditions and permit a maximal utilization of their metallic sites. The dual-metal centers anchored by six pyridinic nitrogen also exhibit wide-ranging catalytic performance. More importantly, the attached OH ligand will likely further tune the ORR activity by modulating the electronic characters at the active centers. This thesis also considered methanol production for DMFCs via direct methane-to-methanol processes enabled by the Cu-oxo complexes anchored in a MOR zeolite framework. Again, DFT was used to determine the most likely the active center configurations under reaction conditions, i.e., Cu-trioxo and bis (µ-oxo) dicopper. The Cu-trioxo configuration was then shown to be particularly active toward the critical C-H bond activation.