Nanoparticle-Decorated Ultrathin La2O3 Nanosheets as an Effcient Electrocatalysis for Oxygen Evolution Reactions

Electrochemical catalysts for oxygen evolution reaction are a critical component for many renewable energy applications. To improve their catalytic kinetics and mass activity are essential for sustainable industrial applications. Here, we report a rare-earth metal-based oxide electrocatalyst comprised of ultrathin amorphous La2O3 nanosheets hybridized with uniform La2O3 nanoparticles(La2O3@NP-NS). Significantly improved OER performance is observed from the nanosheets with a nanometer-scale thickness. The as-synthesized 2.27-nm La2O3@NP-NS exhibits excellent catalytic kinetics with an overpotential of 310 mV at 10 m A cm^-2, a small Tafel slope of 43.1 mV dec^-1, and electrochemical impedance of 38 Ω. More importantly, due to the ultrasmall thickness, its mass activity, and turnover frequency reach as high as 6666.7 A g^-1 and 5.79 s^-1, respectively, at an overpotential of 310 mV. Such a high mass activity is more than three orders of magnitude higher than benchmark OER electrocatalysts, such as IrO2 and RuO2. This work presents a sustainable approach toward the development of highly e cient electrocatalysts with largely reduced mass loading of precious elements.

Thickness-Dependent Piezoelectric Property from Quasi-Two-Dimensional Zinc Oxide Nanosheets with Unit Cell Resolution

A quantitative understanding of the nanoscale piezoelectric property will unlock many application potentials of the electromechanical coupling phenomenon under quantum confinement.In this work,we present an atomic force microscopy-(AFM-)based approach to the quantification of the nanometer-scale piezoelectric property from single-crystalline zinc oxide nanosheets(NSs)with thicknesses ranging from 1 to 4 nm.By identifying the appropriate driving potential,we minimized the influences from electrostatic interactions and tip-sample coupling,and extrapolated the thickness-dependent piezoelectric coefficient(d_(33)).By averaging the measured d_(33) from NSs with the same number of unit cells in thickness,an intriguing tri-unit-cell relationship was observed.From NSs with 3n unit cell thickness(n=1,2,3),a bulk-like d_(33) at a value of~9 pm/V was obtained,whereas NSs with other thickness showed a~30%higher d_(33) of~12 pm/V.Quantification of d_(33) as a function of ZnO unit cell numbers offers a new experimental discovery toward nanoscale piezoelectricity from nonlayered materials that are piezoelectric in bulk.