Engineering Proton-Compatible MIEC Oxide Thin Films for Solid State Electrochemical Systems

Chirag Chotai^a, Federico Baiutti^a, Francesco Chiabrera^a, Lisa Laa^a, Andrea Turino^a, Alex Morata^a, Albert Tarancon^a^,^b

^aInstitut de Recerca en Energia de Catalunya (IREC), Jardins de les Dones de Negre, 1, 2ª pl., 08930, Sant Adrià del Besòs, Barcelona, Spain

^bCatalan Institution for Research and Advanced Studies (ICREA), Passeig de Lluís Companys, 23, 08010 Barcelona, Spain

Proceedings of MATSUS Spring 2026 Conference (MATSUSSpring26)

F5 Lithium Batteries and Beyond: From Fundamentals to Materials Discovery

Barcelona, Spain, 2026 March 23rd - 27th

Organizers: Chia-Chin Chen and Gints Kucinskis

Oral, Chirag Chotai, presentation 503
Publication date: 15th December 2025

Mixed ionic–electronic conductors (MIECs) which can host mobile protons have attracted interest for low- to intermediate-temperature (25ºC - 300 ºC) electrochemical technologies e.g. energy-conversion, sensing and information-processing. However, the challenge remains in determining the proton uptake, electronic leakages and chemical stability when in contact with different media.

In this work, we introduce a thin-film materials comparison of proton-active oxides, combining perovskite-type electrodes (LaSr₀.₄Fe₀.₆O₃, SrFe₀.₅Co₀.₅O₃, Ba₀.₉₅La₀.₀₅Fe₀.₈Zn₀.₂O₃) with widely studied proton storing simple oxides (TiO₂ and WO3). Dense electrode films are deposited using pulsed laser deposition, enabling precise control of thickness, texture and interfaces.

The thin films are characterized using PICET (proton insertion coupled with electron transfer)-inspired electrochemical protocols. Materials are characterized both acidic and alkaline aqueous electrolytes to probe proton-coupled redox processes and their associated charge storage. Cyclic voltammetry and galvanostatic charge-discharge are used to map the accessible potential window, charge insertion per unit cell and rate response for each composition. The evolution of current–potential profiles with pH, scan rate and film thickness provide insight into the balance of near-surface reactions and deeper proton insertion, while extended cycling defines voltage ranges that preserve electrochemical response and structural integrity. This yields a comparative view on how Fe/Co-based perovskites w.r.t Ti/W simple oxides operate as proton-responsive MIECs under different chemical environments. MIEC thin films are also combined with proton conducting perovskites like BaCe₀.₈Y₀.₁Yb₀.₁O₃ and BaZr₀.₄Sc₀.₆O₃ to explore proton insertion using air electrode at relevant temperature ranges.

Overall, this study identifies favorable compositional and microstructural features that govern proton-enabled MIEC behavior. We explored the comparison of proton insertion in MIEC perovskites with simple oxides in different media and proton uptake by hydrogenation of materials with air electrode. The results outline design principles for oxide thin films with tailored protonic and electronic transport, suitable for integration in next-generation intermediate temperature energy storage devices as well as memory devices.

References:

[1] Tang, Yunqing, et al. “Ion Intercalation in Lanthanum Strontium Ferrite for Aqueous Electrochemical Energy Storage Devices.” ACS Applied Materials & Interfaces, vol. 14, no. 16, 12 Apr. 2022, pp. 18486–18497, https://doi.org/10.1021/acsami.2c01379. Accessed 26 Nov. 2025.

[2] Rocca, Tom, et al. “Multivalent-Ion versus Proton Insertion into Nanostructured Electrochromic WO3 from Mild Aqueous Electrolytes.” ACS Applied Materials & Interfaces, vol. 16, no. 18, 24 Apr. 2024, pp. 23567–23575, https://doi.org/10.1021/acsami.4c02152. Accessed 26 Nov. 2025

[3] Isoda, Yosuke, et al. “Stabilization of Oxygen Vacancy Ordering and Electrochemical-Proton-Insertion-And-Extraction-Induced Large Resistance Modulation in Strontium Iron Cobalt Oxides Sr(Fe,Co)Oy.” Nature Communications, vol. 16, no. 1, 2 Jan. 2025, pmc.ncbi.nlm.nih.gov/articles/PMC11696809/, https://doi.org/10.1038/s41467-024-55517-y. Accessed 15 Jan. 2025.

[4] Nikolina Makivić, et al. “Evidence of Bulk Proton Insertion in Nanostructured Anatase and Amorphous TiO 2 Electrodes.” Chemistry of Materials, vol. 33, no. 9, 27 Apr. 2021, pp. 3436–3448, https://doi.org/10.1021/acs.chemmater.1c00840. Accessed 26 Nov. 2025.

[5] Hwang, Sung Hyun, et al. “Triple-Component Composite Cathode for Performance Optimization of Protonic Ceramic Fuel Cells.” International Journal of Hydrogen Energy, vol. 46, no. 67, Sept. 2021, pp. 33551–33560, https://doi.org/10.1016/j.ijhydene.2021.07.179. Accessed 3 Feb. 2025

Acknowledgements:

This work is part of the project POWERDOT, funded by MCIN/AEI/FEDER with PID2022-142003OB-C21. The author acknowledges financial support from an FPI predoctoral fellowship (grant no. PREP2022-000002)

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