ORCID

0000-0001-5300-8434

Keywords

Nanomaterials, Electrocatalysis, Water splitting, Crystal structure, Amorphization

Abstract

This dissertation establishes design principles for earth-abundant catalysts used in the hydrogen evolution reaction (HER), showing that electroactivity is primarily controlled by structural features such as surface facet exposure, dopant content, and dynamic phase transformations. These factors influence conductivity, active site density, and stability, as demonstrated through three model systems: Cu₂O, NiSe₂, and Cu₂S. Cu₂O particles with controlled shapes were synthesized to explore the relationship between facet exposure and catalytic activity. Octahedra dominated by the facet 111 performed better than cubes rich in the facet 100. Combining Cu₂O with reduced graphene oxide further improved conductivity, dispersion, and stability, leading to lower overpotentials and greater durability. NiSe₂ catalysts were made with different selenium levels to examine how stoichiometry and crystal phase affect electronic structure and HER performance. Selenium-rich compositions stabilized the cubic phase, resulting in significantly higher activity and faster kinetics than selenium-deficient samples, highlighting the important role of chalcogen content in controlling catalytic behavior. Cu₂S was found to undergo electrochemical oxidation under reductive HER conditions, forming amorphous CuO domains that developed into Cu(OH)₂. This process provided new mechanistic insights into the unusual oxidation of Cu⁺ to Cu²⁺ during cathodic operation and showed how amorphous-to-crystalline transitions impact catalytic performance. The catalysts exhibited competitive overpotentials and Tafel slopes, with the partial regenerative role of the underlying Cu₂S helping to maintain activity. Overall, these studies demonstrate three complementary strategies for advancing non-precious HER catalysis: tailoring morphology to optimize facet activity, controlling selenium content and crystallinity to stabilize active phases, and understanding oxidation pathways that convert sulfides into oxide-hydroxide heterostructures. These approaches offer a unified framework for designing robust, efficient, and sustainable HER catalysts. Importantly, the insights gained extend beyond Cu- and Ni-based systems, providing transferable guidelines for the rational design of other earth-abundant electrocatalysts.

Completion Date

2025

Semester

Fall

Committee Chair

Lei Zhai

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Chemistry

Format

PDF

Identifier

DP0029742

Document Type

Thesis

Campus Location

Orlando (Main) Campus

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