Files and links (1)
SVY PhD Thesis_0507256.27 MB
Embargoed Access, Embargo ends: 06/26/2027
Dissertation
Scalable nanomanufacturing of cadmium selenide photoanodes for photoelectrochemical hydrogen-producing systems
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.007834
Abstract
Hydrogen is poised to play a transformative role in the global transition to sustainable energy—not only as a clean fuel, but also as a foundational chemical for key industrial sectors such as fertilizer and steel production. Among the technologies being explored for renewable hydrogen generation, photoelectrochemical (PEC) water splitting offers the unique ability to directly convert sunlight and water into storable, zero-carbon hydrogen fuel. However, the scalability of PEC systems remains limited by critical bottlenecks in materials performance, manufacturing yield, and device uniformity--especially when extending from lab-scale to commercially relevant substrate areas.
This dissertation, undertaken as part of a PhD in Chemical Engineering, tackles one of the central challenges in PEC development: the fabrication of large-area, high-efficiency PEC photoelectrodes with reproducible performance and high manufacturing yield. While state-of-the-art III–V tandem devices have achieved record solar-to-hydrogen (STH) efficiencies above 20%, their prohibitive cost and short operational lifetimes preclude large-scale adoption. Meanwhile, low-cost oxide systems offer excellent durability but suffer from insufficient photovoltage and current density for unassisted water splitting. Positioned between these extremes, cadmium-based chalcogenides represent a promising yet underutilized material platform capable of delivering the necessary performance at potentially scalable cost and stability.
The dissertation focuses on cadmium selenide (CdSe), a cadmium chalcogenide semiconductor with excellent optoelectronic properties and favorable band alignment for PEC water splitting. While CdTe, another cadmium-based chalcogenide, is well-established in the photovoltaic industry and a promising bottom-absorber in tandem PEC architectures, its successful pairing for unassisted solar hydrogen production depends critically on a complementary top absorber. This thesis establishes CdSe as a scalable, fault-tolerant top-cell candidate, experimentally laying the groundwork for its integration in dual-junction tandem PEC devices.
In Chapter 2, a robust and low-cost electrochemical method is developed for fabricating planar CdSe thin-film photoelectrodes on transparent conductive substrates. By systematically optimizing deposition potential, charge density, and annealing conditions, the work achieves photocurrent densities of 13.6 mA/cm² and confirms the formation of stoichiometric, phase-pure hexagonal CdSe with strong vertical orientation. These thin films serve as a performance benchmark and a foundation for developing more advanced nanostructured designs.
Chapter 3 introduces a nanowire-based CdSe photoanode architecture, inspired by natural photosynthetic systems and fabricated using anodized aluminum oxide (AAO) templates. By optimizing electrodeposition parameters and post-treatment conditions, nanowire photoanodes achieve record-level PEC performance: a short-circuit current density of 19 mA/cm² and an open-circuit voltage of –920 mV, with demonstrated operational stability over 113 hours under continuous solar illumination. These nanostructured photoelectrodes combine efficient light absorption, enhanced charge separation, and mechanical fault tolerance—key attributes for top-cell performance in tandem PEC designs.
To address the issue of scalability, Chapter 4 demonstrates CdSe nanowire deposition on wafer-scale substrates (100 cm²). Using a novel grid-based and circular masking strategy, the work achieves improved deposition control and suppresses corner-driven field distortions. Devices fabricated using a 16-region circular pattern deliver uniform PEC performance with a Jsc of 7.3 mA/cm², proving that the architecture can be extended to large areas without sacrificing activity.
Chapter 5 focuses on manufacturing yield and deposition uniformity, identifying key sources of non-uniformity—including anodization profile deviations, current crowding, and field asymmetry—and proposing targeted engineering solutions. By implementing current thieving with sacrificial edge electrodes and optimizing reference electrode placement in conjunction with high-conductivity electrolytes, the work achieves spatially uniform nanowire growth across 25 cm² substrates, with variations in nanowire length reduced by more than 50%. These improvements translate directly into higher PEC performance and significantly tighter device-to-device reproducibility.
Collectively, this thesis presents a comprehensive, scalable, and high-yield route to fabricating CdSe-based photoelectrodes suitable for integration into next-generation PEC systems. While tandem CdSe/CdTe integration remains an open experimental direction, this work provides the material, architectural, and process innovations necessary to realize that vision. By overcoming longstanding challenges in large-area nanostructured PEC device manufacturing, this research makes a critical contribution toward practical, affordable, and scalable solar hydrogen production.
Details
- Title: Subtitle
- Scalable nanomanufacturing of cadmium selenide photoanodes for photoelectrochemical hydrogen-producing systems
- Creators
- Shiljashree Vijay
- Contributors
- Syed Mubeen (Advisor)Chris Coretsopoulos (Committee Member)Joe Gomes (Committee Member)Johna Leddy (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemical and Biochemical Engineering
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.007834
- Publisher
- University of Iowa
- Number of pages
- xviii, 214 pages
- Copyright
- Copyright 2025 Shiljashree Vijay
- Language
- English
- Date submitted
- 04/25/2025
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 190-214).
- Public Abstract (ETD)
- Hydrogen fuel is a clean and powerful alternative to fossil fuels—but today, most hydrogen is still produced through carbon-emitting processes. Photoelectrochemical (PEC) water splitting offers a sustainable solution: using sunlight to split water into hydrogen and oxygen with zero emissions. To make this solar hydrogen production viable at scale, we need materials that are not only efficient, but also manufacturable over large areas with high yield. As part of doctoral research in Chemical Engineering, this dissertation tackles one of the most critical challenges in PEC development: how to fabricate large-area hydrogen-producing solar materials that maintain high performance and can be produced reliably. The approach centers on nanostructuring and nanoengineering—specifically growing cadmium selenide (CdSe) nanowires inside anodized aluminum oxide (AAO) templates. These nanowires mimic natural photosynthesis at the nanoscale, capturing sunlight and using it to split water into clean hydrogen fuel. While small-scale devices using these nanowires have shown excellent performance, scaling up to larger sizes has been limited by uneven growth and poor manufacturing yield. This research develops a set of novel electrochemical and process engineering strategies to enable uniform, reproducible CdSe nanowire growth over full 25 cm² and 100 cm² devices. These large-area systems retain the strong performance of their small-scale counterparts and represent a key step toward scalable solar hydrogen technology. The implications are profound. With scalable PEC devices, sunlight can be used not just for electricity, but to produce storable, carbon-free hydrogen fuel—helping bridge the gap between renewable energy supply and demand. This research brings the vision of clean, solar-driven hydrogen closer to reality, offering a pathway toward sustainable fuel production that is both technologically feasible and environmentally essential.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9984831022402771
Metrics
31 Record Views