Producing hydrogen by unassisted solar water splitting is one essential step to make direct solar fuel conversion a viable energy source. To date, however, there has been no demonstration of stable photoelectrodes for high-efficiency photoelectrochemical water splitting. In this work, we report that a GaInP 2 /GaAs/Ge triple-junction (3J) photocathode protected by multifunctional GaN nanostructures can enable both efficient and relatively stable solar water splitting. A 12.6% solar-to-hydrogen (STH) efficiency is measured without any external bias. Of particular importance, we demonstrate relatively stable solar water splitting for 80 h in three-electrode configuration and 57 h in twoelectrode measurement at zero bias. This is the best reported stability for multijunction III-V semiconductor photocathodes in two-electrode configuration to our knowledge. The multifunctional GaN nanostructure significantly reduces the charge transfer resistance at the semiconductor/electrolyte interface and protects III−V materials against corrosion. Such multifunctional GaN photocatalytic nanostructures provide a new pathway to improve the performance of conventional photoelectrodes to achieve both efficient and stable unassisted solar water splitting.
In conventional superconductors an external magnetic field generally suppresses superconductivity. This results from a simple thermodynamic competition of the superconducting and magnetic free energies. In this study, we report the unconventional features in the superconducting epitaxial thin film tungsten telluride (WTe2). Measuring the electrical transport properties of Molecular Beam Epitaxy (MBE) grown WTe2 thin films with a high precision rotation stage, we map the upper critical field Hc2 at different temperatures T. We observe the superconducting transition temperature Tc is enhanced by in-plane magnetic fields. The upper critical field Hc2 is observed to establish an unconventional non-monotonic dependence on temperature. We suggest that this unconventional feature is due to the lifting of inversion symmetry, which leads to the enhancement of Hc2 in Ising superconductors.
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