Engineering carbide nanoparticles coated with noble metal monolayers for catalysis

Abstract

The noble metals (NMs) comprise ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). Together, these corrosion-resistant elements serve as nature's universal catalysts by binding reactant molecules neither too strongly nor too weakly. This allows for rapid catalytic transformations of reactants into useful products. Modern society, its current technologies, and its emerging renewable energy technologies are underpinned by precious metal catalysts. However, the noble metals are the least abundant elements in the lithosphere, making them prohibitively scarce and expensive for future global-scale technologies. Furthermore, the traditional catalyst engineering toolkit is ill-equipped to optimize the reactivity, stability, and loading of NM catalysts. The technologies developed in this thesis have two overarching implications. First, a method is developed to engineer non-sintered and metal-terminated transition metal carbide (TMC) nanoparticles. Featuring "noble metal-like" surface reactivity, TMCs are earth-abundant and exhibit many useful catalytic properties, such as carbon monoxide and sulfur tolerance. By designing TMC nanoparticles with controlled surface properties, this thesis offers new avenues for replacing noble metal catalysts with inexpensive alternatives. Second, a method is developed to synthesize TMC nanoparticles coated with atomically-thin noble metal monolayers. This offers new directions for improved catalyst designs by substantially enhancing reactivity and stability while reducing overall noble metal loadings. These synthetic achievements in nanoscale core-shell catalyst engineering were guided by computational quantum chemistry, model thin film studies, and advanced spectroscopic techniques. Examination of the catalytic utility of these new materials was performed in the context of water electrolysis, proton exchange membrane fuel cells, direct methanol fuel cells, and high temperature thermal reforming.