Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Coridan, Robert H.

Committee Member

Chen, Jingyi

Second Committee Member

Kilyanek, Stefan M.

Third Committee Member

Heyes, Colin D.

Fourth Committee Member

Stenken, Julie A.

Keywords

atomic layer deposition; back contact; cupric oxide; photoelectrochemistry; protection layer

Abstract

In the search for a sustainable method to meet increasing energy needs, solar energy emerges as an underutilized, plentiful resource. Solar intermittency and requirements for transportation necessitate storing solar energy in the form of chemical bonds via artificial photosynthesis. Photoelectrochemical (PEC) water splitting generates hydrogen fuel from solar energy and water. A semiconducting material that successfully meets the complex requirements for building an industrially scalable PEC device has yet to emerge. This is leading to a reevaluation of materials previously overlooked within PEC research, mainly materials with limitations such as minimal charge carrier mobility and propensity to corrosion under illumination in aqueous environments. Cupric oxide (CuO) is one such candidate semiconductor, energetically suitable as a photocathode for PEC water splitting, and possesses both limitations mentioned above. Hierarchical three-dimensional structuring can circumvent the charge mobility limitations of CuO while maintaining its ability to absorb maximal incident solar illumination. Our proposed method of hierarchical structuring is coating nanometer-thick layers of CuO across a three-dimensional conductive scaffold of silica spheres, which maintains the path length of illumination through the semiconductor. Atomic Layer Deposition (ALD) can be used throughout construction of a PEC device based on this scaffold. In this work, the transparent conducting oxide (TCO) Al:ZnO (AZO) deposited using ALD is proposed as a conductive layer in hierarchical structuring of a PEC device. AZO is soluble in the extreme pH environments often present in current PEC water splitting research. An ultra-thin film of ALD-TiO2 is evaluated as a protection layer for AZO from chemical dissolution. This protection layer work is further applied to intervening in CuO photocorrosion. Additionally, we studied the impact the work function of a back contact in the PEC performance of protected CuO electrodes. We conclude with a discussion on the viability of CuO as a material for three-dimensional structuring in the proposed scaffold.

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