Date of Award

Spring 2026

Language

English

Embargo Period

3-18-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Nanoscale Science and Engineering

Program

Nanoscale Engineering

First Advisor

Haralabos Efstathiadis

Second Advisor

Iulian Gherasiou

Committee Members

Daniele Cherniak, Kyoung-Yeol Kim, Mengbing Huang

Keywords

Anion Exchange Membrane Electrolyzer, Hydrogen Evolution Reaction, MoNi Alloy; Electrocatalysis, Ionomer-Free Electrodes, Catalyst Layer Engineering

Subject Categories

Analytical Chemistry | Atomic, Molecular and Optical Physics | Catalysis and Reaction Engineering | Condensed Matter Physics | Industrial Engineering | Inorganic Chemistry | Materials Chemistry | Membrane Science | Metallurgy | Nanoscience and Nanotechnology | Nanotechnology Fabrication | Semiconductor and Optical Materials | Sustainability

Abstract

Anion exchange membrane water electrolysis (AEMWE) presents a promising pathway toward cost-effective and sustainable hydrogen production by integrating the chemical robustness of alkaline systems with the compact, zero-gap design of proton exchange membrane electrolyzers. However, the widespread implementation of AEMWE is limited by the availability of highly active and durable platinum-group-metal (PGM)-free catalysts and by an incomplete understanding of their degradation behavior under realistic operating conditions.

This dissertation focuses on the development, characterization, and mechanistic investigation of nanostructured MoNi4–MoO2-based electrodes for efficient and stable hydrogen generation under alkaline and membrane-integrated environments. MoNi4–MoO2 nanorods were synthesized through a hydrothermal method, followed by reductive annealing and were further modified with a MoVN overlayer using dual DC(V)/RF(Mo) magnetron co-sputtering. The resulting MoVN/MoNi4–MoO2 composite exhibited enhanced bifunctional catalytic activity, achieving overpotentials of 14 mV for the hydrogen evolution reaction (HER) and 244 mV for the oxygen evolution reaction (OER) at 10 mA cm-2 in 1 M KOH. The combined presence of metallic MoNi4, conductive MoO2, and surface MoVN nitrides improved charge-transfer kinetics, surface stability, and electrochemically active area, contributing to the catalyst’s superior performance in both half-cell reactions.

The optimized MoNi4–MoO2 catalyst was subsequently employed as a cathode in an ionomer-free, catalyst-coated-substrate (CCS) configuration with a Fumasep FAS-50 membrane. The symmetric MoNi4||MoNi4 AEMWE cell delivered 400 mA cm-2 at 2.0 V and 60 °C, maintaining stable operation beyond 24 hours and exhibiting gradual voltage rise over 100 hours. To understand the origins of performance decay and identify degradation mechanisms, a comprehensive diagnostic framework combining Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA), and X-ray Photoelectron Spectroscopy (XPS) was developed. RBS depth profiling confirmed a well-defined bilayer structure comprising a metallic MoNi4-rich surface supported by a MoO2-rich subsurface, with elemental redistribution confined to the near-surface region after extended operation.

Time-resolved XPS analysis revealed the progressive oxidation of metallic Mo species to Mo6+ and the simultaneous formation of Ni(OH)2 and NiOOH, indicating that surface passivation is the dominant degradation pathway. Complementary NRA provided quantitative hydrogen depth profiles, showing an initial hydrogen concentration of approximately 9–10 atomic percent localized within the top 40 nm of the MoNi4-rich region, which decreased to about 3 atomic percent after 100 hours of operation. This hydrogen depletion correlated strongly with the observed molybdenum leaching, nickel hydroxide formation, and increased charge-transfer resistance, thereby establishing a direct relationship between hydrogen dynamics and catalyst degradation.

The combined electrochemical and ion-beam analyses presented in this work offer an unprecedented view of how hydrogen accumulation, diffusion, and desorption processes influence both structural stability and long-term performance in PGM-free electrodes. Overall, this dissertation establishes a mechanistic understanding of degradation pathways in Mo–Ni–O systems and demonstrates an integrated diagnostic approach that bridges the gap between electrochemical behavior and nanoscale material transformations. The insights gained from this study provide a scientific foundation for the rational design of durable, high-performance electrodes and scalable architectures for next-generation AEM water electrolyzers.

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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