Research Project: Mekanik Alasımlama Ve Kinetik Kontrollü Lazer Sentezi Ile Mikro Ve Nano Soy Olmayan Yüksek Entropi Katalizörlerinin Üretimi, Karakterizasyönü Ve Karsılastırılması
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Contributors
Funders
ID
TB.00739
Authors
Jahangiri, Hadi
Researcher
Publications
Open-Air pulsed laser-deposited NiCoCuFeMoMnO x high-entropy oxide thin films for efficient electrocatalytic oxygen evolution reaction
(Amer Chemical Soc, 2025) Mahdavi, Hossein; Alamdari, Armin Asghari; Ünal, Uğur; Jahangiri, Hadi; Mahdavi, Hossein; Alamdari, Armin Asghari; KUYTAM (Koç University Surface Science and Technology Center); Graduate School of Sciences and Engineering; Department of Chemistry; KUHyTech (Koç University Hydrogen Technologies Center); Yes; Research Center; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Sciences
High-entropy materials have garnered significant attention as possible non-noble metal-based electrocatalysts for the production of hydrogen via water electrolysis. High-entropy oxides demonstrate high activity and stability at relatively low costs. This study presents the synthesis and characterization of NiCoCuFeMoMnO x high-entropy oxide thin films deposited on graphite substrates via open-air pulsed laser deposition for electrocatalytic oxygen evolution reaction. The pulsed laser deposition process facilitates the oxidation of high-entropy alloy targets, forming a stable oxide phase. X-ray diffraction patterns reveal a mixture of amorphous (28.3%) and face-centered cubic crystalline (71.7%) phases. Morphological analysis using scanning electron microscopy and transmission electron microscopy shows a porous, flower-like structure, enhancing surface area and active site availability. Electrochemical measurements demonstrate significant improvements in oxygen evolution reaction performance with reduced overpotentials down to 180 +/- 7 mV to reach 10 mAcm-2 and enhanced reaction kinetics. The high-entropy oxide films maintain stability over 100 h, showing improved catalytic efficiency after long-term stability measurements. Electrochemically active surface area and electrochemical impedance spectroscopy analyses indicate increased active surface area and reduced charge transfer resistance. These results highlight NiCoCuFeMoMnO x high-entropy oxide films as promising robust electrocatalysts for efficient water splitting.
Optimization of laser-wavelength dependence for open-air atmospheric pressure pulsed laser deposition of AlCrFeMnTi high-entropy alloy for tailored surface properties
(American Chemical Society, 2024) Alamdari, Armin Asghari; Jahangiri, Hadi; Kepçeoğlu, Abdullah; Mahdavi, Hossein; Ünal, Uğur; Yağcı, Mustafa Barış; Department of Chemistry; Graduate School of Sciences and Engineering; KUYTAM (Koç University Surface Science and Technology Center); Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Research Center
High-entropy alloys (HEAs) have garnered significant attention in different fields due to their exceptional mechanical and physical properties, making them promising candidates for various applications. Several techniques, including physical vapor deposition and pulsed laser deposition (PLD), have been employed for the fabrication of HEA thin films. In this study, we explore a novel approach to synthesizing the lightweight HEA (LWHEA) AlCrFeMnTi using PLD in air at atmospheric pressure with a particular focus on the influence of the laser wavelength on the deposition process and the resulting alloy characteristics. This research investigates the impact of different laser wavelengths on the LWHEA's characterization and the optimization of laser wavelength dependence in air at atmospheric pressure PLD of LWHEA AlCrFeMnTi for tailored surface properties such as phase composition, microstructure, and corrosion resistance. Systematically varying the laser wavelength was attempted to optimize the deposition conditions. This was aimed at achieving enhanced properties and precise control over the alloy's composition. This work contributes to a deeper understanding of the open air PLD process for LWHEAs and sheds light on the role of the laser wavelength in tailoring their properties, which can have significant implications for the development of advanced materials for aerospace, automotive, and other high-performance applications. Ultimately, this research aims to provide valuable insights into the design and fabrication of LWHEAs with tailored properties through laser-based deposition techniques.
Boron-doped NiCoCuMoMn high-entropy alloys for enhanced electrocatalytic water splitting: An experimental and computational study
(Amer Chemical Society, 2025) Ünal, Uğur; Jahangiri, Hadi; Mahdavi, Hossein; Mahdavi, Hossein; Mansoor, Maryam; Ergen, Onur; Department of Chemistry; KUYTAM (Koç University Surface Science and Technology Center); KUHyTech (Koç University Hydrogen Technologies Center); Graduate School of Sciences and Engineering; Yes; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Sciences; Research Center
High-entropy alloys offer a versatile platform for electrocatalysis, yet their optimization has so far been dominated by transition-metal compositional tuning. Here, we present the first demonstration of boron doping as a powerful nonmetal strategy to engineer high-entropy alloys for water splitting. Incorporating boron into NiCoCuMoMn HEAs drives a dramatic increase in the BCC phase fraction, refines crystallite sizes from the nanometer to subnanometer scale, and induces lattice distortions that create quasi-vacancy active sites. These unique structural modulations, validated by X-ray diffraction, Raman spectroscopy, and electron microscopy, are corroborated by first-principles calculations, showing that substitutional boron lowers oxygen adsorption energies and accelerates oxygen evolution reaction kinetics. As a result, the boron-doped HEA exhibits a breakthrough reduction in the oxygen evolution reaction overpotential (from 300 to 200 mV at 10 mA cm-2) and a sharp decrease in the Tafel slope (from 185 to 110 mV dec-1) while maintaining long-term stability over 48 h. Although the hydrogen evolution activity is moderately suppressed, this trade-off further confirms the boron-induced modulation of surface energetics. This combined experimental and theoretical study establishes boron doping as a design strategy for high-entropy alloy electrocatalysts, providing mechanistic evidence that nonmetal incorporation can rival metal compositional tuning in dictating catalytic performance.
Mixing enthalpy-driven variations in ablation thresholds and laser-induced crater morphologies of CoCuFeNiMnMox (x=0.5, 1.0, 1.5) high-entropy alloys under UV nanosecond laser pulses
(Elsevier, 2025) Mahdavi, Hossein; Kepçeoğlu, Abdullah; Alamdari, Armin Asghari; Ünal, Uğur; Jahangiri, Hadi; Mahdavi, Hossein; Alamdari, Armin Asghari; KUYTAM (Koç University Surface Science and Technology Center); Department of Chemistry; Graduate School of Sciences and Engineering; Yes; Research Center; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
This study investigates the ablation threshold fluence and power dependence of ablation process in CoCuFeNiMnMox (x = 0.5, 1.0, and 1.5) high-entropy alloys under ultraviolet nanosecond laser pulses. The ablation threshold value, a critical parameter determining the minimum energy density required for laser material removal, is explored in-depth. Mixing enthalpy, characterizing the energy change during the formation of solid solutions, is calculated for the alloys, shedding light on their atomic interactions and phase stability. Laser- induced crater morphologies are analyzed using white light interferometry and optical microscopy, showing distinct features influenced by laser fluence and pulse number. Results demonstrate that an increase in laser pulse energy correlates with an increase in standard deviation. The relationship between crater size, laser pulse energy, and ablation depth is examined, highlighting the alloys' diverse ablation thresholds.
Mechanically alloyed NiCuMnWX (X = Co, Fe, or Mo) high-entropy alloy electrocatalysts for alkaline water splitting
(Royal Society of Chemistry, 2025) Ünal, Uğur; Jahangiri, Hadi; Mahdavi, Hossein; Mahdavi, Hossein; Alamdari, Armin Asghari; Quinson, Jonathan; Department of Chemistry; KUYTAM (Koç University Surface Science and Technology Center); KUHyTech (Koç University Hydrogen Technologies Center); Yes; College of Sciences; Research Center
High-entropy alloys have great potential as electrocatalysts for water-splitting reactions. Benefiting from the cocktail effect and lattice distortion, high-entropy alloys exhibit relatively low overpotentials and significant stability, making them excellent candidates for electrocatalytic water splitting. These materials offer a cost-effective and abundant alternative to conventional noble-metal catalysts such as Pt and IrO2, which are limited by high costs and scarcity. This study investigates the electrocatalytic performance of high-entropy alloy powders prepared with equimolar ratios of Ni, Cu, Mn, and W, with additional elements (Co, Fe, or Mo) introduced to optimize their activity for the hydrogen evolution reaction and oxygen evolution reaction. The high-entropy alloy powders are synthesized via ball milling, involving both dry milling and wet milling in ethanol, followed by washing and drying at room temperature. Comprehensive characterization techniques, including X-ray diffraction, field-emission scanning electron microscopy, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, are employed to analyze their structure and properties. Electrochemical studies reveal that Fe and Mo significantly enhance hydrogen evolution reaction activity, achieving overpotentials of 301 mV and 305 mV, respectively, with corresponding Tafel slopes of 200.9 mV dec-1 and 153.3 mV dec-1. Meanwhile, Co incorporation improves oxygen evolution reaction performance, reducing the overpotential to 326 mV with a Tafel slope of 143.7 mV dec-1. These findings underscore the potential of high-entropy alloy powders for advancing renewable energy technologies.
