Novel Anodes Based on High Entropy Oxides for Water Electrolysis

Authors

• Joseph Talley, University of Nebraska-LincolnFollow

First Advisor

Bai Cui

Date of this Version

8-2026

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Mechanical Engineering and Applied Mechanics

Under the supervision of Professor Bai Cui

Lincoln, Nebraska, August 2026

Comments

Copyright 2026, Joseph Talley. Used by permission

Abstract

Hydrogen production by alkaline water electrolysis is rate limited by the slow oxygen evolution reaction at the anode. This thesis examined Fe–Co–Ni–Cr high-entropy spinel oxides containing controlled amounts of Ti to determine how Ti concentration, phase formation, surface chemistry, and electrophoretic deposition affected catalyst performance and coating stability. Oxide powders were synthesized using a glucose- and ammonium sulfate assisted method, characterized by X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, deposited onto nickel substrates by electrophoretic deposition, and tested electrochemically in 1 M KOH.

The principal products retained a cubic spinel type structure, but rutile TiO₂ became detectable when the Ti concentration reached approximately 50% of the equimolar target and above. The samples containing approximately 25% and less of the equimolar Ti concentration showed no detectable TiO₂ phase. X-ray photoelectron spectroscopy indicated predominantly Cr³⁺, Ti⁴⁺, and Ni²⁺ character together with mixed Fe²⁺/Fe³⁺ and Co²⁺/Co³⁺ states. A chemically reasonable cation distribution model was consistent with a partially inverted spinel, although tetrahedral and octahedral site occupancy could not be confirmed directly. Electrophoretic deposition produced porous coatings containing fine agglomerates and larger platelet like particles. Comparisons of fresh and residual powders indicated that deposition affected surface composition more strongly than bulk composition, including Ni depletion and Co and Cr enrichment at the residual powder surface. The optimized washed HEO required approximately 338 mV overpotential to reach 10 mA cm^-2 and 555 mV to reach 100 mA cm^-2. HEO coatings also exhibited more consistent high current behavior and better post-test retention than the Ti free oxide.

These results demonstrate that Ti can be incorporated and beneficially modify the spinel catalyst, but its effect depends on whether it remains incorporated within the spinel structure or segregates as TiO₂. Overall performance was governed by the combined effects of phase composition, surface redox chemistry, electrophoretic transport, coating structure, and mechanical stability rather than Ti concentration alone.

Advisor: Bai Cui