Developing stable and efficient electrocatalysts is vital for boosting oxygen evolution reaction (OER) rates in sustainable hydrogen production. High-entropy oxides (HEOs) consist of five or more metal cations, providing opportunities to tune their catalytic properties toward high OER efficiency. This work combines theoretical and experimental studies to scrutinize the OER activity and stability for spinel-type HEOs.
View Article and Find Full Text PDFACS Appl Mater Interfaces
April 2021
In this work, we report the presence of surface-densified phases (β-NiO, γ-NiO, and δ-NiO) in LiNiO (LNO)- and LiNiAlO (LNA)-layered compounds by combined atomic level scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). These surface phases form upon electrochemical aging at high state of charge corresponding to a fully delithiated state. A unique feature of these phases is the periodic occupancy by Ni in the Li layer.
View Article and Find Full Text PDFIron oxide nanomaterials participate in redox processes that give them ideal properties for their use as earth-abundant catalysts. Fabricating nanocatalysts for such applications requires detailed knowledge of the deposition and growth. We report the spontaneous deposition of iron oxide nanoparticles on HOPG in defect areas and on step edges from a metal precursor solution.
View Article and Find Full Text PDFBulk magnetic materials with the noncentrosymmetric cubic B20 structure are fascinating due to skyrmion spin structures associated with Dzyaloshinskii-Moriya interactions, but the size of skyrmions are generally larger than 50 nm. The control of such spin structures in the 10 nm size ranges is essential to explore them for spintronics, ultra-high-density magnetic recording, and other applications. In this study, we have fabricated MnSi nanoparticles with average sizes of 9.
View Article and Find Full Text PDFEnabling practical utilization of layered R3̅m positive electrodes near full delithiation requires an enhanced understanding of the complex electrode-electrolyte interactions that often induce failure. Using Li[NiCoAl]O (NCA) as a model layered compound, the chemical and structural stability in a strenuous thermal and electrochemical environment was explored. Operando microcalorimetry and electrochemical impedance spectroscopy identified a fingerprint for a structural decomposition and transition-metal dissolution reaction that occurs on the positive electrode at full delithiation.
View Article and Find Full Text PDFMn-based silicides are fascinating due to their exotic spin textures and unique crystal structures, but the low magnetic ordering temperatures and/or small magnetic moments of bulk alloys are major impediments to their use in practical applications. In sharp contrast to bulk Mn5Si3, which is paramagnetic at room temperature and exhibits low-temperature antiferromagnetic ordering, we show ferromagnetic ordering in Mn5Si3 nanoparticles with a high Curie temperature (Tc ≈ 590 K). The Mn5Si3 nanoparticles have an average size of 8.
View Article and Find Full Text PDFNanoscience has been one of the outstanding driving forces in technology recently, arguably more so in magnetism than in any other branch of science and technology. Due to nanoscale bit size, a single computer hard disk is now able to store the text of 3,000,000 average-size books, and today's high-performance permanent magnets--found in hybrid cars, wind turbines, and disk drives--are nanostructured to a large degree. The nanostructures ideally are designed from Co- and Fe-rich building blocks without critical rare-earth elements, and often are required to exhibit high coercivity and magnetization at elevated temperatures of typically up to 180 °C for many important permanent-magnet applications.
View Article and Find Full Text PDFFormation of chemically ordered compounds of Fe and Au is inhibited in bulk materials due to their limited mutual solubility. However, here we report the formation of chemically ordered L12-type Fe3Au and FeAu3 compounds in Fe-Au sub-10 nm nanoparticles, suggesting that they are equilibrium structures in size-constrained systems. The stability of these L12-ordered Fe3Au and FeAu3 compounds along with a previously discovered L10-ordered FeAu has been explained by a size-dependent equilibrium thermodynamic model.
View Article and Find Full Text PDFWe present simple, self-assembled, and robust fabrication of ultrahigh density cobalt nanowire arrays. The binary Co-Al and Co-Si systems phase-separate during physical vapor deposition, resulting in Co nanowire arrays with average diameter as small as 4.9 nm and nanowire density on the order of 10(16)/m(2).
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