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Abstract: The positive effect of intermetallic ordering of platinum alloy nanoparticles on oxygen reduction reaction (ORR) activity has been well established. What is still missing is an understanding of selective leaching of the less noble metal from the ordered structure and its correlation to longterm ORR performance. Using a combination of kinetic Monte Carlo simulations and advanced characterization techniques, we provide unprecedented insight into dealloying of intermetallic PtCu3 nanoparticles a well-known binary alloy. Comparison of ordered and disordered samples with identical initial compositions and particle size distributions reveals an unexpected correlation: whereas the copper dealloying rates in the ordered and disordered counterparts are almost the same, in the ordered structure Pt atoms are surrounded by 15−30% more Cu atoms throughout all the stages of acid leaching. This more convenient Pt−Cu coordination explains the statistically significant increase of 23−37% in ORR activity of the ordered structure at all stages of alloy degradation.
Found in: osebi
Keywords: ORR activity, fuel cells, platinum alloy, nanoparticle stability, intermetallic ordering, kinetic Monte Carlo, dealloying, in situ ICP-MS
Published: 27.09.2016; Views: 3182; Downloads: 0
Fulltext (3,27 MB)

Abstract: Nitrogvajakoli so rumeno obarvane spojine, ki prispevajo k absorpciji rjavega ogljika v ozračju. Na podnebje vplivajo z absorbiranjem svetlobe v bližnjem UV in vidnem delu spektra, saj po absorpciji sproščajo toploto, kar vodi v ogrevanje ozračja. Poleg tega imajo škodljiv vpliv tudi na ekosistem. Prisotnost v ozračju in njihovi mehanizmi nastanka so že raziskani, mehanizmi razpadanja v vodni fazi ozračja pa so malo znani. V tem delu smo raziskali, kako sončna svetloba vpliva na staranje nitrogvajakolov v ozračju. Z uporabo fotospektroskopije smo najprej proučili spektroskopske lastnosti vodnih raztopin gvajakola, 4-nitrogvajakola, 5-nitrogvajakola in dinitrogvajakola ter kako nanje vpliva pH. Preiskovani nitrogvajakoli v vidnem delu spektra močno absorbirajo le pri visokih pH, dinitrogvajakol pa zaradi nekoliko nižjega pKa absorbira tudi že pri rahlo kislih pH vrednostih. pH raztopin 4-nitrogvajakola in 5-nitrogvajakola različnih koncentracij smo pred fotolizo prilagodili na vrednost atmosferskih vod (pH okoli 5), nato pa smo jih izpostavili sončnemu simulatorju z močjo enega sonca. Produkte fotorazgradnje smo ločili in identificirali s tekočinsko kromatografijo sklopljeno s pretočnim spektrometrom in tandemskim masnim spektrometrom (LC-UV/Vis-MS/MS). Fotorazgradnja nitrogvajakolov poteka zelo počasi. Najdeni produkti imajo ohranjen aromatski obroč in eno ali več nitro skupin (dinitrogvajakol, 4-nitrokatehol). Zaključimo lahko, da so nitrogvajakoli v vodni fazi ozračja obstojni, absorbirajo v širokem območju pH vrednosti in s svojimi absorpcijskimi lastnostmi skupaj s produkti fotorazgradnje prispevajo k vplivu rjavega ogljika na podnebje.
Found in: osebi
Keywords: Rjavi ogljik, nitrogvajakol, fotorazpad, spektroskopske lastnosti, vpliv pH, identifikacija produktov, LC-UV/Vis-MS/MS
Published: 03.06.2020; Views: 1407; Downloads: 61
Fulltext (1,62 MB)

Abstract: The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiONx) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by various state-of-the-art materials’ characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO2 benchmarks as well as the Ir-supported samples on morphologically different TiONx from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.
Found in: osebi
Keywords: electrocatalysis, oxygen-evolution reaction, TiONx-Ir powder catalyst, iridium nanoparticles, anodic oxidation, morphology−activity correlation
Published: 04.01.2021; Views: 666; Downloads: 0
Fulltext (6,36 MB)