Defense of the dissertation of Suleimenova Diana for the degree of Doctor of Philosophy (PhD) in the educational program «8D05306 - Chemistry»

The defense of the dissertation for the degree of Doctor of Philosophy (PhD) by Suleimenova Diana on the topic «Synthesis of cathode materials based on transition metal chalcogenides and their application for dye-sensitized solar cells» in the educational program «8D05306 – Chemistry» will be held at the L.N. Gumilyov Eurasian National University.

The dissertation was carried out at the «Chemistry education department» of L.N. Gumilyov Eurasian National University.

The language of defense is english

Official reviewers:

Ongarbayev Yerdos Kalimullauly – Doctor of Chemical Sciences, Professor, Al-Farabi Kazakh National University (Almaty, Republic of Kazakhstan);

Tileuberdi Erbol – PhD, Associate Professor, Abay Kazakh National Pedagogical University (Almaty, Republic of Kazakhstan).

Temporary members of the Dissertation Council:

Numan Arshid - PhD, Associate Professor, Sunway University (Subang Jaya, Malaysia);

Argimbayeva Akmaral Mukhambetovna – Candidate of Chemical Sciences, Associate professor (docent), Al-Farabi Kazakh National University (Almaty, Republic of Kazakhstan);

Lepikhin Maxim Sergeevich – PhD, senior researcher, Laboratory of Electrochemical Production Technology (Almaty, Republic of Kazakhstan).

Scientific advisors:

Tashenov Yerbolat Ordabekovich – PhD, Acting docent, Department of Chemistry, L.N. Gumilyov Eurasian National University (Astana, Republic of Kazakhstan);

Robert J. O'Reilly – PhD, Medical doctor (MD), Lecturer at the School of Science and Technology University of New England (Armidale, Australia).

The defense will take place on May 13, 2026, at 03:00 PM in the Dissertation Council for the training direction «8D053 – Physical and chemical sciences» in the educational program «8D05306 – Chemistry» of L.N. Gumilyov Eurasian National University. The defense meeting is planned to be held online.

Link: https://teams.microsoft.com/meet/44389222445215?p=TATAOg28rKnkaPEigA 

Address: Kazhymukan Street, 13, Room: 333, Astana

Abstract (English): ABSTRACT of the dissertation work of Diana Suleimenova on the topic «Synthesis of cathode materials based on transition metal chalcogenides and their application for dye-sensitized solar cells» submitted for the degree of Doctor of Philosophy (PhD) in the educational program 8D05306 – Chemistry General description of the work. The dissertation work is devoted to the development, synthesis, and comprehensive investigation of platinum-free electrocatalytic cathode materials (CM) for application in photoelectrochemical and photovoltaic devices, in dye-sensitized solar cells (DSSCs, also known as Gratzel cells). The main results of the dissertation work are presented in a series of scientific publications and focus on the development, investigation, and application of transition metal chalcogenide (TMC)-based CM as an efficient and economically viable alternative to platinum (Pt) in DSSCs. Relevance of the research topic. In the context of a global energy crisis, the depletion of traditional energy sources, and the worsening environmental situation, there is an increasing need to develop alternative, sustainable, and environmentally friendly methods of electricity generation. Among the various solutions, solar cells attract particular attention as one of the most promising sources of renewable energy. DSSCs stand out among other photovoltaic devices due to their simple fabrication process, low cost, and ability to operate efficiently under diffuse light conditions. However, one of the key limitations to their widespread industrial adoption remains the need to improve energy conversion efficiency, durability, and device stability. The cathode plays a crucial role in the operation of DSSCs, as its properties significantly influence the redox couple regeneration rate and, consequently, the overall efficiency of the device. Traditionally, Pt is used as CM. Pt is the most employed CM in DSSCs due to its ability to facilitate efficient electron transport at the cathode and support the regeneration of oxidized dye molecules. Moreover, Pt effectively promotes the reduction of oxidized species in the electrolyte because of its low overpotential for the reduction reaction. However, one of the main drawbacks of using Pt as a cathode is its high cost, which limits the scalability and affordability of DSSCs. In addition, Pt can degrade and oxidize in liquid electrolytes, particularly when the I-/I3- redox couple is used, leading to stability issues. In recent years, extensive efforts have been made to develop Pt-free CMs. An ideal material should not only be low-cost but also exhibit excellent electrocatalytic activity for triiodide reduction and high chemical stability. Among the various materials studied, TMCs - such as metal oxides, sulfides, and selenides - stand out due to their impressive electrocatalytic performance, chemical stability and wide availability. Thus, the topic of this doctoral dissertation, focused on the synthesis and investigation of DSSCs based on TMCs as CMs, is both contemporary and highly relevant. Purpose of the study: synthesis of cathode materials for dye-sensitized solar cells based on transition metal chalcogenides and to study their catalytic activity. Research tasks: 1. Design and synthesis of cathode materials based on transition metal chalcogenides. 2. Characterization of the structure and morphology of the synthesized electrocatalysts using modern analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). 3. Evaluation of the catalytic activity of the synthesized electrocatalysts as cathode materials for DSSCs. The objects of the study are CEs based on transition metal chalcogenides. Main provisions submitted for defense: 1. It has been established that the ternary sulfide Zn0.76Co0.24S, synthesized by a one-step solvothermal method on an FTO substrate, is an efficient and economically viable CM for DSSCs. It has been shown that Zn0.76Co0.24S exhibits higher cathodic current density than Pt, indicating enhanced electrocatalytic activity, while achieving comparable power conversion efficiency (PCE) (7.94% vs. 8.12%). It has been experimentally confirmed that the material demonstrates superior long-term stability, maintaining performance after 200 h of operation. 2. It has been established that a three-step solvothermal synthesis of FeCo2S4 nanowires make it possible to obtain a CM with reduced charge-transfer resistance (RCT ≈ 5.54 Ω•cm2) compared to Pt (≈ 7.07 Ω•cm2). It was shown that DSSCs based on FeCo2S4 nanowires achieve higher PCE (7.88% vs. 7.45%). These photovoltaic devices have been shown to have improved operational stability, whereas Pt-based cells show performance degradation. 3. It has been established that the ternary composite MWCNT@MnO/NiS is a highly efficient and low-cost CM for DSSCs. It has been shown that the use of this composite results in a high-PCE of 9.29%, exceeding that of Pt (8.54%). It has been experimentally confirmed that the low charge-transfer resistance (RCT ≈ 0.53 Ω•cm2) ensures high electrocatalytic activity and long-term operational stability. Scientific Novelty: - For the first time, new CEs based on ternary sulfide FeCo2S4 and a ternary composite MWCNTs@MnO/NiS have been synthesized and characterized. These materials exhibit high electrocatalytic activity in the I-/I3- reduction reactions in DSSCs. - A relationship has been established between the composition, morphology, structural parameters, and catalytic activity of the synthesized materials, enabling the identification of key factors influencing their efficiency as alternatives to Pt in DSSCs. - It has been demonstrated that the use of FeCo2S4 and Zn0.76Co0.24S enables the achievement of significant current densities and redox pair regeneration rates, comparable to or exceeding those of benchmark Pt electrodes. - A novel approach has been proposed for creating a composite CEs based on multi-walled carbon nanotubes (MWCNTs) modified with MnO/NiS (MWCNTs@MnO/NiS), providing a synergistic effect due to the high conductivity of the carbon matrix and the catalytic activity of transition metals. - A comprehensive physicochemical and electrochemical investigation of the synthesized CEs was carried out using XRD, SEM, EDS, TEM, XPS, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), allowing for a substantiated assessment of their potential for practical application in DSSCs. Theoretical significance of the study. The theoretical significance of the work lies in the advancement of understanding of the physicochemical properties of TMCs as promising CMs for photovoltaic devices. The study provides new insights into the influence of morphology, crystal structure, and chemical composition on their electrochemical and optical characteristics, thereby deepening the understanding of charge transport processes and material-photosensitizer interactions in DSSC architectures. The obtained results expand the theoretical framework in the fields of chemistry, materials science, nanotechnology, and electrochemical energy conversion, and contribute to research and development efforts in renewable energy technologies by opening new approaches to the engineering of functional nanostructures for efficient solar energy conversion. Practical significance of the study. The practical significance of the study lies in the development and validation of efficient CEs based on TMCs, which can be applied in DSSCs. The synthesized materials demonstrated enhanced properties, including high electrical conductivity, catalytic activity, and stability, contributing to increased solar energy conversion efficiency and reduced production costs of solar cells. The developed synthesis methods are reproducible, scalable, and adaptable for industrial use. The research outcomes can be applied in the development of next-generation, low-cost, and environmentally friendly photovoltaic devices, as well as in related fields such as biosensors, supercapacitors, lithium-ion batteries, electrochromic devices, fuel cells, and catalytic systems. Relations to research programs. The research was supported by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grants № AP13068358 – «Inexpensive solid-state dye sensitized solar cells - a new industry development strategy», № AP23490505 - «Indoor photovoltaics based on solid-state dye-sensitized solar cells of advanced architecture»). The author’s personal contribution includes the formulation of the research aim and objectives, the execution of experimental work, the interpretation and presentation of the obtained results, and the preparation of scientific articles for publication in international journals related to the dissertation topic. All results presented in this work were obtained independently by the author or with their direct involvement. In the first article entitled “Tailored Manganese Oxide and Nickel Sulfide Composites with MWCNTs as Platinum-Free Electrodes for Solar Energy Conversion”, the author performed the main experiments and data analysis, wrote the draft manuscript text. In the second article entitled “Enhanced Efficiency and Stability of Dye-Sensitized Solar Cells Utilizing FeCo2S4 Nanowires as Pt-Free Counter Electrodes”, the author contributed to the Software, Resources, Methodology, Formal analysis, Data curation, Conceptualization. In the third article entitled “Efficient One-Step Synthesis of a Pt-Free Zn0.76Co0.24S Counter Electrode for Dye-Sensitized Solar Cells and Its Versatile Application in Photoelectrochromic Devices”, the author contributed to the methodology, investigation, writing - original draft preparation. Publications: Based on the results and conclusions of the dissertation research, 4 scientific works have been published, including 3 articles in international peer-reviewed journals indexed in Scopus and Web of Science with a non-zero impact factor, 1 article in a journal recommended by the Committee for Quality Assurance under the Ministry of Science and Higher Education, Kazakhstan; 4 presentations at an international conference and one patent of the Republic of Kazakhstan. List of publications based on the research results: 1. Diana Suleimenova, Yerbolat Tashenov, Ayagoz Ibrayeva, Robert J. O’Reilly, Bakhytzhan Baptayev, Mannix P. Balanay. Tailored Manganese Oxide and Nickel Sulfide Composites with MWCNTs as Platinum-Free Electrodes for Solar Energy Conversion // Scientific Reports – 2025. - V. 15., Iss.1. – Article number 29723. https://doi.org/10.1038/s41598-025-14954-5 The article is indexed in the Web of Science Core Collection and Scopus databases. At the time of its publication in 2025, the journal «Scientific Reports» had an impact factor for 2024 of 3.9 and a Q1 quartile in multidisciplinary sciences. It has a CiteScore for 2024 of 6.7 and a multidisciplinary percentile of 89. 2. Diana Suleimenova, Yerbolat Tashenov, Bakhytzhan Baptayev, Mannix P. Balanay. Enhanced Efficiency and Stability of Dye-Sensitized Solar Cells Utilizing FeCo2S4 Nanowires as Pt-Free Counter Electrodes // Journal Photochemistry and Photobiology A: Chemistry. - 2024, - V. 457. Article number 115908. https://doi.org/10.1016/j.jphotochem.2024.115908 The article is indexed in the Web of Science Core Collection and Scopus databases. At the time of its publication in 2024, the journal «Photochemistry and Photobiology A: Chemistry» had an Impact Factor for 2023 of 4.1 and a Q2 quartile in physical chemistry. It had a CiteScore for 2023 of 7.9, with a percentile of 86 in general physics and astronomy, 81 in general chemical engineering, and 81 in general chemistry. 3. Yerbolat Tashenov, Diana Suleimenova, Bakhytzhan Baptayev, Salimgerey Adilov, Mannix P. Balanay. Efficient One-Step Synthesis of a Pt-Free Zn0.76Co0.24S Counter Electrode for Dye-Sensitized Solar Cells and Its Versatile Application in Photoelectrochromic Devices // Nanomaterials. – 2023. - V. 13., Iss.20. – Article number 2812. https://doi.org/10.3390/nano13202812 The article is indexed in the Web of Science Core Collection and Scopus databases. At the time of its publication in 2023, the journal «Nanomaterials» had an Impact Factor for 2022 of 5.3 and a Q2 quartile in multidisciplinary chemistry and multidisciplinary materials science. It had a CiteScore for 2022 of 7.4, with a percentile of 81 in general chemical engineering and 78 in general materials science. In publications recommended by the authorized body: 4. Diana Suleimenova, Yerbolat Tashenov, Mannix P. Balanay, Bakhytzhan Baptayev. Unveiling the Potential of MnxCo3-xS4 Electrocatalyst in Triiodide Reduction for Dye-Sensitized Solar Cells // Bulletin of the Karaganda University. Physics Series. – 2023. - V. 111., № 3. – P. 58-64. https://doi.org/10.31489/2023ph3/58-64 List of presentations at international conferences: 5. Diana Suleimenova, Ayagoz Ibrayeva, Bakhytzhan Baptayev, Yerbolat Tashenov, Mannix P. Balanay. Pt-free and efficient counter electrode with nanostructured MnCo2S4 for dye-sensitized solar cells. // The 10 International Conference on Nanomaterials and Advanced Energy Storage Systems, INESS-22, August 4-6, 2022, Nur-Sultan, Kazakhstan. 6. Diana Suleimenova, Yerbolat Tashenov, Bakhytzhan Baptayev, Mannix P. Balanay. Pt-free and efficient counter electrode with FeCo2S4 nanowires for dye-sensitized solar cells. // The 12th International Conference on Nanomaterials and Advanced Energy Storage Systems (INESS-2024), August 7-9, 2024, Nazarbayev University, Astana, Kazakhstan. 7. Diana Suleimenova, Bakhytzhan Baptayev, Mannix P. Balanay. FeCo2S4 nanowires as an effective counter electrode for dye-sensitized solar cells. // NU Annual Research Conference 2024, September 19-21, 2024, Nazarbayev University, Astana, Kazakhstan. 8. Diana Suleimenova, Bakhytzhan Baptayev, Mannix P. Balanay. Efficient dye-sensitized solar cells with easily fabricated Pt-free MnxOy/Ni3S4/MWCNT composite counter electrodes. // The 4th International Symposium on Emerging Materials and Devices, hosted by the Renewable Energy Lab at National Laboratory Astana, May 28-30, 2025, Nazarbayev University, Kazakhstan. One patent of the Republic of Kazakhstan: 9. Utility Model Patent No. 11168 dated September 19, 2025: Suleimenova D.A., Ibrayeva A.K., Balanay M.P., Baptayev B.D. "Method of production of electrocatalyst for dye-sensitized solar cells".

Dissertation

List of Scientific Works

Consultant's Review

Foreign Consultant's Review

Conclusion of the Research Ethics Committee