Ambient Deposition of Single Atoms for Enhancement of Nanostructured Metal Oxide Electrode Catalytic Performance

Single-atom decoration represents cutting-edge technology for enhancing heterogeneous catalysis by utilizing the unique capabilities of catalysts at the atomic level. However, the high surface energy of single atoms often causes them to aggregate, forming nanoparticles [1]. To address this challenge, we first modify the surface structure by synthesizing nanostructured support layers, such as TiO 2 nanotubes, TiO 2 nanosheets, and NiO nanosponge. Especially TiO 2 nanotubes and NiO nanosponge pose relevant support layers due to their favorable attributes, including a high surface-to-volume ratio, abundance, and excellent chemical stability, while TiO 2 nanosheets serve as model system. Vertically aligned, well-ordered, self-organized oxide nanostructures can be conveniently fabricated through anodization, allowing precise control over the geometry of the nanotubes and nanopores [2,3]. Well-defined atomic-scale defects on the surface of the supports are generated to immobilize single-atom co-catalysts. Therefore, defect engineering techniques typically require high-temperature thermal reduction. We present more gentle defect-engineering approaches, including room-temperature sonochemical treatment or UV-light irradiation. By combining these approaches, we are able to effectively trap Pt and Ir single atoms. We present a direct method utilizing UV-light radiation to induce point defects, specifically Ti 3+ and oxygen vacancies (V O ) onto the surface of TiO 2 nanosheets and efficiently decorate them with Pt single atoms [4]. Our findings demonstrate that sonochemically treated TiO 2 nanotubes provide a remarkable substrate for single-atom decoration from dilute solutions, resulting in promising performance in H 2 evolution catalysis and renewable energy conversion. Additionally, the role of V single-atom decoration in ultrasonic treatment of support materials is investigated. Thermal annealing in a reductive atmosphere induces the formation of numerous defects, facilitating the anchoring of single Ir atoms onto the surface of annealed NiO nanostructures. Additionally, the novel ultrasound-driven method stabilizes these Ir atoms within the porous structure. By employing both approaches, we effectively trap Ir single atoms, thereby enhancing the efficiency of the oxygen evolution reaction in electrocatalysis [5]. The characterization of the electrodes is conducted using microscopy techniques (FESEM, TEM, and HAADF-STEM) and spectroscopy (XPS and ToF-SIMS) [6]. Gas chromatography is employed to evaluate the H 2 photocatalytic performance of TiO 2 electrodes, while linear sweep voltammetry is utilized to assess the H 2 and O 2 electrochemical activity of NiO electrodes [5]. Our findings highlight the significant enhancement of photo- and electrocatalytic efficiency of nanostructured oxide electrodes modified with highly stable single-atom co-catalysts by gentle treatments. References [1] L. Zhang, X. Zhao, Z. Yuan, M. Wu, H. Zhou, Oxygen defect-stabilized heterogeneous single atom catalysts: preparation, properties and catalytic application, J. Mater. Chem. A. 9 (2021) 3855–3879. https://doi.org/10.1039/D0TA10541D [2] S. Hejazi, S. Pour-Ali, M.S. Killian, S. Mohajernia, One-dimensional suboxide TiO 2 nanotubes for electrodics applications, Electrochem. Commun. 136 (2022) 107246. https://doi.org/10.1016/j.elecom.2022.107246. [3] U. Sultan, F. Ahmadloo, G. Cha, B. Gökcan, S. Hejazi, J.E. Yoo, N.T. Nguyen, M. Altomare, P. Schmuki, M.S. Killian, A High-Field Anodic NiO Nanosponge with Tunable Thickness for Application in p-Type Dye-Sensitized Solar Cells, ACS Appl. Energy Mater. 3 (2020) 7865–7872. https://doi.org/10.1021/acsaem.0c01249. [4] S. Hejazi, S. Mohajernia, B. Osuagwu, G. Zoppellaro, P. Andryskova, O. Tomanec, S. Kment, R. Zbořil, P. Schmuki, On the Controlled Loading of Single Platinum Atoms as a Co-Catalyst on TiO 2 Anatase for Optimized Photocatalytic H 2 Generation, Adv. Mater. 32 (2020) 1908505. https://doi.org/10.1002/adma.201908505. [5] S. Hejazi, H. Mehdi-pour, C.O. Otieno, J. Müller, S. Pour-Ali, M. Shahsanaei, S.S. Tafreshi, B. Butz, M.S. Killian, S. Mohajernia, Room-temperature defect-engineered titania: An efficient platform for Pt single atom decoration for photocatalytic H 2 evolution, Int. J. Hydrogen Energy. 51 (2024) 222–233. https://doi.org/10.1016/j.ijhydene.2023.08.126. [6] K. Toukabri, S. Hejazi, M. Shahsanaei, S. Pour-Ali, A. Kosari, B. Butz, M.S. Killian, S. Mohajernia, Spontaneous Deposition of Single Platinum Atoms on Anatase TiO 2 for Photocatalytic H 2 Evolution, Langmuir. 40 (2024) 4661–4668. https://doi.org/10.1021/acs.langmuir.3c03316.

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