ABSTRACT
Electrocatalysts in acidic media face the issues of inactivation and degradation with complex thermodynamic processes. A density functional theory (DFT) calculation is performed to investigate the galvanic and pitting etching processes of metal@Pt (M@Pt) core-shell nanoparticles (12 transition elements are selected to replace the core atoms). The dissolution process with atomic etching follows the dissolution potential site-dependence phenomena, and the dissolution potential of the Pt shell exhibits a negative linear correlation with the average d-band center of the Pt shell. We have found that the specific shape effect, core-shell contact area and period effect all affect the potential difference at each step in the dissolution process. Meanwhile, the core atom segregation reduces the dissolution potential to form defects on the outermost shell, which is the driving force of halogen-pitting. By analyzing the 12 core elements and M@Pt nanoparticles of three specific shapes, Ir@Pt nanoparticles with a TCO-structure exhibit a high initial potential in multistep dissolution process throughout the galvanic etching process and good performance with respect to pitting corrosion and are strong candidates for nanoparticle catalysts.
ABSTRACT
Barium strontium zirconate titanate ceramics ((BaSr)(ZrTi)O3-BSZT) with Zr4+ ionic contents of 15 and 20 mol % and Sr2+ ionic contents of 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. X-ray diffraction and scanning electron microscopy were used to characterize the lattice structure and morphologies of the ceramics. Permittivity and polarization as a function of temperature were characterized using an impedance analyzer and a Tower-Sawyer circuit. The electrocaloric effect was measured directly and calculated using the Maxwell relation (indirectly). The results indicated that the BSZT ceramics change from a normal ferroelectric to a relaxor ferroelectric with increasing Zr4+ ionic content, which can be further modified by the addition of Sr2+ ionic content. The optimized adiabatic temperature change Δ T obtained is 2.43 K in (Ba0.85Sr0.15)(Zr0.15Ti0.75)O3 ceramics, and Δ T >1.6 K over a wide temperature span of 120 °C was obtained.
ABSTRACT
Barium zirconate titanate (BZT) (Ba(ZrxTi1-x)O3) ceramics with Zr4+ contents of x = 5, 10, 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. The microstructures, morphologies, and electric properties were characterized using X-ray diffraction, scanning electron microscopy, and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The electrocaloric effect adiabatic temperature change decreases with the increasing Zr4+ content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol % of Zr4+ ionic content.
