Date of Award

Spring 2022

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

John R. Regalbuto

Second Advisor

John R. Monnier

Abstract

Ultrasmall supported platinum nanoparticles (Pt NPs) are often used in two promising renewable energy production technologies – hybrid-sulfur water splitting for actively catalyzing H2SO4 decomposition and in fuel cells for the oxygen reduction reaction (ORR). However, the stability of Pt NPs under reaction conditions is the ultimate challenge for these processes. Two prevalent ways to overcome this challenge are improving stability by anchoring Pt onto a secondary metal or doping heteroatoms into the support. This dissertation covers the rational design, synthesis, and stabilization of Pt-based catalysts in these two ways to achieve durable catalytic performance with desired activity and selectivity.

The first vein of this research explores the stabilization of core-shell structured Ir-Pt bimetallic NPs on pre-stabilized titania (TiO2) or boron nitride (BN) support for high-temperature H2SO4 decomposition, particularly SO3 to SO2 decomposition. A series of Ir-Pt catalysts have been synthesized with different Ir loading and evaluated for the selective decomposition of SO3 to SO2 in an extreme (high temperature, highly corrosive) reaction environments. Investigations have revealed that the deactivation of Ir-Pt catalyst on pre-stabilized TiO2 is more dominant than BN, confirmed by X-ray diffraction and catalyst evaluation results. Furthermore, a negligible catalyst deactivation has been obtained for 1\%Pt-7.5\%Ir/BN. Various characterization techniques have been employed to explain this consistent stability.

In the second vein of research, the stabilization of Pt NPs by nitrogen-doped carbon has been explored with a combination of high sensitivity X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) with in-situ pretreatment. The high sensitivity XRD instrument has allowed the incredibly observationed the behavior of ultrasmall Pt NPs (about 1 nm), which was previously impossible to observedetect. Furthermore, the XRD results have been clarified the unappreciated trend in the literature of why XRD peaks of ultrasmall Pt NPs often appear shifted to the left. Additionally, using XPS, this work has been corrected a prevalent literature delusion that higher valences of Pt in N-doped carbon result from the formation of Pt-N bond.

In the final part of this work, the strong electrostatic interaction (SEA) technique has been explored to synthesize small, uniformly distributed, and highly dispersed Pt NPs on Vulcan XC72R carbon (Pt/C). The SEA method has significantly improved catalyst durability for ORR in proton-exchange membrane fuel cells (PEMFCs) by tuning metal-support interactions, confirmed by a comparative durability study in PEMFCs on various Pt/C catalysts prepared by dry and wet impregnation, polyol, and SEA methods. In addition, a thermal stability test has been performed based on these Pt/C catalysts that have validated the superiority SEA catalyst by demonstrating the metal-support interactions.

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