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Dissertation
Rapid and scalable manufacturing of cadmium telluride nanowires for enhanced photoelectrochemical hydrogen production
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2025
DOI: 10.25820/etd.008171
Abstract
Hydrogen is emerging as a cornerstone of a zero-carbon energy economy. As an industrial feedstock and chemical energy carrier, global hydrogen demand is expected to rise to 180 million tons by 2030, driven by applications spanning synthetic fuels, fertilizers, steel production, and long-duration energy storage. Today, over 95% of hydrogen is produced using fossil fuels through steam methane reforming, releasing approximately 830 million tons of CO₂ annually. Replacing this with low-carbon production is essential for achieving global climate goals.
Among the various hydrogen production routes, water electrolysis powered by renewable electricity has received substantial attention. Yet, even in its most optimized form, electrolyzer-based hydrogen remains costly, with production costs around $4–5/kg—still far above the U.S. Department of Energy’s long-term target of $1/kg. An alternative approach is solar water splitting through photoelectrochemical (PEC) systems, which generate hydrogen directly from sunlight and water using semiconductor materials. PEC systems eliminate the need for separate photovoltaic panels and electrolyzers, offer simpler integration, and reduce balance-of-system complexity. However, scalable fabrication of high-performing PEC devices has remained a central challenge, largely due to limitations in material synthesis, device architecture, and long-term stability.
This dissertation addresses these challenges by developing a solution-processed platform for rapid and scalable fabrication of CdTe/CdSexTe(1–x) nanowire heterostructures for PEC hydrogen production. CdTe is a compelling material for solar water splitting due to its near-optimal bandgap (1.45 eV), high absorption coefficient (>10⁵ cm⁻¹), and established synthesis infrastructure. Shaping CdTe into vertically aligned nanowires further enhances performance by increasing light trapping, shortening carrier transport paths, and reducing material usage. Yet, the widespread application of CdTe nanowires in PEC systems has been limited by the difficulty of growing high-quality nanowires on a scale. Vapor-based methods offer limited compositional control, while conventional electrodeposition—despite being low-cost and precise—has been hampered by extremely slow growth rates, typically <10 nm/min, rendering it impractical for large area manufacturing.
To overcome this bottleneck, we developed a rapid electrodeposition method capable of synthesizing CdTe nanowires at a rate of 500 nm/min—an improvement of over 50× compared to prior techniques. This was achieved by systematically tuning the electrolyte composition (notably increasing TeO₂ concentration to10 mM and controlling pH to ~0.3), operating at optimized cathodic potentials (-0.68 V vs. Ag/AgCl), and performing controlled post-annealing at 400 °C. These conditions allowed us to overcome mass transport limitations and achieve precise stoichiometry, crystallinity, and morphological uniformity in the resulting nanowire arrays. Structural and compositional analysis via XRD and SEM-EDS confirmed the formation of high-quality cubic CdTe nanowires with minimal Te oxide inclusion, a key indicator of stoichiometric balance.
Building upon this high-throughput platform, we next engineered a compositionally tunable CdSexTe(1–x) nanowire bottom layer using a voltage-programmed co-deposition strategy. This allowed continuous modulation of the Se:Te ratio by controlling the deposition potential in a single electrolyte bath. By integrating this CdSexTe(1–x) segment beneath the CdTe layer, we created a heterostructured nanowire with a built-in compositional gradient. This CdSexTe(1–x) layer served two key functions: (i) it acted as a “compositional sink” for excess tellurium during thermal annealing, absorbing Te diffusing from the CdTe segment and thus eliminating Te-rich defects, and (ii) it formed a favorable band-aligned junction that enhanced photovoltage and suppressed recombination. The resulting CdTe/CdSexTe(1–x) nanowire heterostructures exhibited outstanding performance as photocathodes for PEC hydrogen evolution. Under standard AM 1.5G illumination, the devices achieved a photoconversion efficiency of 9.0% with an onset potential of -0.97 V vs. RHE and sustained operation for over 25 hours without significant performance degradation. These results represent the highest reported efficiency for CdTe-based nanowire PEC photoelectrodes to date and demonstrate that high performance and stability can be achieved simultaneously in solution-grown nanostructured architectures.
The dissertation makes three central contributions to the field of PEC solar hydrogen generation. First, it establishes a high-throughput, low-temperature, and scalable method for growing CdTe nanowires with precise control over structure and composition. Second, it introduces a novel voltage-controlled alloying strategy to create compositionally graded CdSexTe(1–x) layers within nanowires, enabling both functional bandgap tuning and chemical defect mitigation. Third, it demonstrates how these material and architectural advances can be integrated into a stable, high-efficiency PEC device that operates under realistic solar conditions.
Beyond the immediate scientific findings, this work advances the broader goal of producing hydrogen directly from sunlight and water in a cost-effective and scalable manner. By simplifying the device architecture, eliminating the need for separate PV and electrolyzer components, and leveraging rapid solution processing, the results move PEC technology closer to commercial viability. Moreover, the methods developed here are not limited to CdTe—they can be adapted to other chalcogenide systems, alloy compositions, or tandem configurations for broader solar fuel applications.
In summary, this dissertation presents a cohesive, stepwise approach to tackling the fundamental and practical limitations of nanowire-based solar water splitting. The innovations reported here offer a credible path toward low-cost, scalable solar hydrogen production and provide new design principles for future PEC technologies targeting the DOE’s $1/kg H₂ milestone.
Details
- Title: Subtitle
- Rapid and scalable manufacturing of cadmium telluride nanowires for enhanced photoelectrochemical hydrogen production
- Creators
- Samuel Abayomi Adesanoye
- Contributors
- Syed Mubeen (Advisor)Joe Gomes (Advisor)Chris Coretsopoulos (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
- Summer 2025
- DOI
- 10.25820/etd.008171
- Publisher
- University of Iowa
- Number of pages
- xxviii, 276 pages
- Copyright
- Copyright 2025 Samuel Abayomi Adesanoye
- Language
- English
- Date submitted
- 07/29/2025
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 236-276).
- Public Abstract (ETD)
Hydrogen is expected to play a major role in the world s clean energy future. It can be used to power vehicles, produce fertilizers, and store renewable electricity. But today, nearly all hydrogen is produced using fossil fuels a process that emits over 800 million tons of carbon dioxide every year. To meet growing demand while reducing emissions, we need new technologies that produce hydrogen cleanly, efficiently, and affordably.
One of the most promising approaches is solar water splitting, where hydrogen is generated directly from sunlight and water, without the need for electricity or fossil fuels. In this method, special semiconductors are used to absorb sunlight and drive the water-splitting reaction. While this process has great potential, it has not yet reached widespread use. The main barriers are high cost, slow manufacturing methods, and the limited durability of existing materials.
This dissertation tackles those challenges by developing a new way to grow semiconductor nanowires made of cadmium telluride (CdTe), a material already widely used in solar cells. Nanowires offer several advantages over flat films: they use far less material, capture more sunlight, and can help move charges more efficiently. However, making high-quality nanowires quickly and at scale has been difficult especially with the level of control needed for water-splitting applications.
To solve this, a new high-speed, low-temperature process was developed to grow CdTe nanowires using an inexpensive, solution-based method. By adjusting the chemistry and operating conditions, the growth rate was increased more than fiftyfold compared to previous methods without sacrificing quality. The process was further extended to create nanowires with precise compositional control, introducing selenium to form an alloy called CdSexTe(1 x). This bottom layer acts as a compositional sink, capturing excess elements during heating, improving the device structure, and enhancing hydrogen production.
The final result is a nanowire-based system that reaches 9% solar-to-hydrogen conversion efficiency and can operate for over 25 hours without major degradation both record-setting achievements for this class of materials. These devices are made entirely through scalable, low-cost techniques and offer a clear path toward larger systems for real-world use.
By combining fast manufacturing, smart material design, and device integration, this work brings solar hydrogen technology significantly closer to commercial viability. It opens new possibilities for producing clean hydrogen using only sunlight and water providing a blueprint for sustainable energy systems of the future.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9984948640602771
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