Processes used in colloidal chemistry can be jointly exploited to make complex metal alloy nanoparticles.

The oxygen evolution reaction is the bottleneck to energy-efficient water-based electrolysis for the production of hydrogen and other solar fuels. In proton exchange membrane water electrolysis (PEMWE), precious metals have generally been necessary for the stable catalysis of this reaction. In this work, we report that delamination of cobalt tungstate enables high activity and durability through the stabilization of oxide and water-hydroxide networks of the lattice defects in acid. The resulting catalysts achieve lower overpotentials, a current density of 1.8 amperes per square centimeter at 2 volts, and stable operation up to 1 ampere per square centimeter in a PEMWE system at industrial conditions (80°C) at 1.77 volts; a threefold improvement in activity; and stable operation at 1 ampere per square centimeter over the course of 600 hours.

The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented. A variety of shorter and longer segments of zinc-blende or wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.

The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high‐surface area nickel boride (Ni_xB) nanosheets as a low‐cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm⁻² at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V at 20 mA cm⁻² when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X‐ray absorption fine‐structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni‐B under OER conditions, owing to a Ni‐B core@nickel oxyhydroxide shell (Ni‐B@NiO_xH) structure, and increase in disorder of the NiO_xH layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution.

Graphitic carbon nitride (g-C₃N₄), a metal-free semiconductor with a band gap of 2.7 eV, has received considerable attention owing to its fascinating photocatalytic performances under visible-light. g-C₃N₄ exhibits high thermal and chemical stability and non-toxicity such that it has been considered as the most promising photocatalyst for environmental improvement and energy conservation. Hence, it is of great importance to obtain high-quality g-C₃N₄ and gain a clear understanding of its optical properties. Herein, we report a high-yield synthesis of g-C₃N₄ products via heating of high vacuum-sealed melamine powder in an ampoule at temperatures between 450 and 650 °C. Using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the chemical composition and crystallization of the as-produced g-C₃N₄ are demonstrated. A systematic optical study of g-C₃N₄ is carried out with several approaches. The optical phonon behavior of g-C₃N₄ is revealed by infrared and Raman spectroscopy, and the emission properties of g-C₃N₄ are investigated using photoluminescence (PL) spectroscopy, while the photocatalytic properties are explored by the photodegradation experiment.