Morphology-Tuned Pt3 Ge Accelerates Water Dissociation to Industrial-Standard Hydrogen Production over a wide pH Range.

The discovery of novel materials for industrial-standard hydrogen production is the present need considering the global energy infrastructure. A novel electrocatalyst, Pt3 Ge, which is engineered with a desired crystallographic facet (202), accelerates hydrogen production by water electrolysis, and records industrially desired operational stability compared to the commercial catalyst platinum is introduced. Pt3 Ge-(202) exhibits low overpotential of 21.7 mV (24.6 mV for Pt/C) and 92 mV for 10 and 200 mA cm-2 current density, respectively in 0.5 m H2 SO4 . It also exhibits remarkable stability of 15 000 accelerated degradation tests cycles (5000 for Pt/C) and exceptional durability of 500 h (@10 mA cm-2 ) in acidic media. Pt3 Ge-(202) also displays low overpotential of 96 mV for 10 mA cm-2 current density in the alkaline medium, rationalizing its hydrogen production ability over a wide pH range required commercial operations. Long-term durability (>75 h in alkaline media) with the industrial level current density (>500 mA cm-2 ) has been demonstrated by utilizing the electrochemical flow reactor. The driving force behind this stupendous performance of Pt3 Ge-(202) has been envisaged by mapping the reaction mechanism, active sites, and charge-transfer kinetics via controlled electrochemical experiments, ex situ X-ray photoelectron spectroscopy, in situ infrared spectroscopy, and in situ X-ray absorption spectroscopy further corroborated by first principles calculations.

Epitaxial Growth of GaAs Nanowires on Synthetic Mica by Metal-Organic Chemical Vapor Deposition.

The epitaxial growth of III-V nanowires with excellent optoelectronic properties on low-cost, light-weight, and flexible substrates is a key step for the design and engineering of future optoelectronic devices. In our study, GaAs nanowires were grown on synthetic mica, a two-dimensional layered material, via vapor-liquid-solid growth using metal-organic chemical vapor deposition. The effect of basic epitaxial growth parameters such as temperature and V/III ratio on the vertical yield of the nanowires is investigated. A vertical yield of over 60% is achieved at an optimum growth temperature of 400 °C and a V/III ratio 18. The structural properties of the nanowires are investigated using various techniques including scanning electron microscopy, high-resolution transmission electron microscopy, and high-angle annular dark-field imaging. The vertical nanowires grown at a low temperature and a high V/III ratio are found to have a zincblende phase with a [111] B polarity. The optical properties are investigated by photoluminescence (PL) and time-resolved PL measurements. First-principles electronic structure calculations within the framework of density functional theory elucidate the van der Waals nature of the nanowire/mica interface. Our results also show that these nanowires can be easily lifted off the bulk 2D mica template, providing a pathway for flexible nanowire devices.