Graduate Studies

 

First Advisor

Vitaly Alexandrov

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemical and Biomolecular Engineering

Date of this Version

8-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Engineering (Materials Engineering)

Under the supervision of Professor Vitaly Alexandrov

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Mohammadreza Reza Nouri. Used by permission

Abstract

Understanding charge transfer mechanisms of electrochemical reactions is critical for advancing a variety of electrochemical energy storage and conversion technologies such as water electrolysis, fuel cells, and batteries. (Photo)electrochemical water splitting, involving OER at the anode and HER at the cathode, presents an environmentally friendly way of storing energy from renewable sources in the form of pure hydrogen. While a lot of emphasis has been placed on developing highly active and stable OER/HER catalysts, our atomic-level understanding of the underlying charge transfer mechanisms falls behind.

In this work, we focus on both Faradaic and non-Faradaic charge transfer mechanisms to investigate their effect on the overall catalytic performance under OER/HER conditions. We employ the DFT methodology along with the computational hydrogen electrode (CHE) approach to examine the thermodynamics of a series of catalysts under reaction conditions. The Faradaic (classical) charge transfer mechanism involves the flow of current through the interface by means of redox reactions. The non-Faradaic mechanism involves non-classical effects where charge carriers traverse energy barriers via quantum tunneling.

To study the classical charge transfer we focus on water-splitting electrocatalysis at the surfaces of the [alpha]-SnWO4 photoanode. DFT-based thermodynamic calculations are carried out to construct surface phase/Pourbaix diagrams to analyze facet-dependent stability and OER activity of [alpha]-SnWO4 photoanode.

The non-classical electron transfer mechanism via quantum-mechanical tunneling is studied in a model Pt/water system that is comprised of three main parts: electrode, electrolyte, and the electrochemical (EC) STM tip. This theoretical study is inspired by the identification of tunneling noise features in the EC-STM measurements of various water-splitting electrocatalysts in the collaborator’s laboratory. The Quantum-ATK code is used to compute electronic transmission and current-voltage characteristics. The goal of this project is to evaluate theoretical feasibility of distinguishing between different reaction intermediates through electron tunneling calculations and the role of aqueous media in non-classical charge transfer.

In the final chapter, we analyzed irreversibility of certain LIB cathode materials caused by electrocatalytic generation of oxygen gas during charge-discharge cycling that in turn triggers transition metal migration into the interlayer space. Here, we discuss two similar materials (Ru- and Ir-based oxides) and compare their thermodynamic ability to generate oxygen gas, as well as kinetic barriers for transition metal migration.

Advisor: Vitaly Alexandrov

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