Studying activity and stability of ultra-low loading Ir oxide electrodes for water electrolysis and green hydrogen generation
Water electrolysis is a crucial technology for producing hydrogen with reduced CO2 footprint, which is essential for decarbonizing various sectors and achieving a sustainable future. Proton Exchange Membrane (PEM) water electrolyzers are particularly attractive due to their high efficiency compared to alkaline electrolyzers, compact design, and ability to operate at high current densities[1]. The process of water electrolysis involves two half-cell reactions: the Hydrogen Evolution Reaction (HER) at the cathode and the Oxygen Evolution Reaction (OER) at the anode. OER has a slower kinetics, making it a limiting factor for the overall process efficiency[2]. Therefore, enhancing the OER kinetics is vital for improving the performance of PEM electrolyzers. Ruthenium and iridium (in the form of ruthenium and iridium oxides) are among the most active OER electrocatalysts, with the latter showing superior stability and the former showing superior activity[2]. However, iridium's high cost necessitates increasing its intrinsic activity to reduce its loading – without performance losses – to make significant advancements in hydrogen production through PEM electrolysis, while also meeting the catalyst loading targets set by the US DOE of <500 μg cm-2[1,3].
One effective strategy to reduce the catalyst loading is to use catalysts in the form of ultra-thin films or nanoparticles (NPs), so to achieve a high catalyst surface area. Recently, our group used the phenomenon of solid-state dewetting[4,5] to fabricate Pt NPs as electrocatalyst on fluorine-doped tin oxide (FTO) electrodes for the electrochemical HER[6]. Dewetting is a phenomenon where thin metal films (~20 nm) subjected to heat agglomerate to form NPs. The figure a and b illustrate the process of dewetting and an SEM micrograph of Pt NPs on FTO, respectively. Traditional “wet” chemistry methodologies for fabricating nanoparticle-based electrodes result in electrocatalysts with complex morphology, chemical composition, and structure. Dewetting, instead, is a binder-free approach by which the NPs are directly formed on the desired substrate which provides a scalable chemical-free route to fabricated catalyst-coated electrodes.
a) from ref. 4; b,c) from ref. 6; d) unpublished results by Houtz, Harsha and Altomare.
This approach of fabricating electrocatalyst NPs can enhance the intrinsic HER activity, thus allowing to use ultra-low Pt loadings and attaining a reasonable HER kinetics (Fig c). The enhanced activity can be ascribed to electronic metal-support interaction (EMSI), wherein, a charge transfer occurs from the support (FTO) to the catalyst (Pt). The charge transfer is known
a) b) c) d)
to occur due to a difference in the work function (Φ) of the catalyst and the support, where electrons transfer from the material with a lower work function to the material with a higher work function. See more in this press release on our research!
A master’s assignment was undertaken earlier in 2024 to fabricate IrOx thin films and NPs on suitable electrode material for electrochemical OER, using sputtering and dewetting methods. Preliminary results provided a foundation for studying such electrodes under hydrodynamic conditions. Efforts were made to find the right conditions for sputter-depositing and thermally-treat Ir films on a suitable electrode (figure d shows an SEM micrograph of dewetted Ir NPs), testing such electrocatalysts as rotating disk electrodes (for enhanced mass transfer), which is essential to study the OER performance. The preliminary work also investigated how to activate, i.e., oxidize the Ir electrocatalysts (thermally or electrochemically) and aimed at designing a protocol for testing the electrodes OER activity and stability.
Further experiments are needed to investigate more in detail how IrOx thin films and NPs perform in the OER and how stabile these are. This master assignment is designed to get a deeper understanding of the role of thermal treatments on IrOx thin films and NPs as a catalyst for OER and answer the following research questions:
1.
What is the role of the thermal treatment on the crystallinity, phase composition, and oxidation state of Ir in IrOx?
2.
How do these properties affect the activity and stability of IrOx towards OER?
3.
Does the thermal treatment causes EMSI? And if so, does it favor the OER kinetics?
In this project, there are opportunities to interact with the Dutch research organization TNO and companies Vsparticle (NL) and Hystar (NOR).
Working on this project, you will deal with the following activities:
a.
Prepare electrodes of IrOx thin films and NPs.
b.
Use analytical techniques and process the data to characterize the electrodes and study their morphology, structure, and composition. Analytical techniques could include scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).
c.
Use electrochemical characterization techniques such as cyclic voltammetry and linear sweep voltammetry for testing the OER activity.
d.
Use electrochemical characterization techniques such as chronoamperometry and chronopotentiometry to test the electrode stability during the OER.
e.
Use existing literature to interpret and compare the results obtained in the lab.
Contacts
Shreyas Harsha, PhD candidate, s.harsha@utwente.nl
Prof. Marco Altomare, m.altomare@utwente.nl
Dept. Chemical Engineering, MESA+ Institute for Nanotechnology, University of Twente
References
[1] S. Wang, A. Lu, C. J. Zhong, Nano Converg 2021, 8, 1.
[2] T. Naito, T. Shinagawa, T. Nishimoto, K. Takanabe, Inorg Chem Front 2021, 8, 2900.
[3] Technical Targets for Proton Exchange Membrane Electrolysis | Department of Energy.
[4] M. Altomare, N. T. Nguyen, P. Schmuki, Chem Sci 2016, 7, 6865.
[5] C. V. Thompson, Annu Rev Mater Res 2012, 42, 399.
[6] S. Harsha, R. K. Sharma, M. Dierner, C. Baeumer, I. Makhotkin, G. Mul, P. Ghigna, E. Spiecker, J. Will, M. Altomare, Adv Funct Mater 2024, 2403628.