Optimization of CuO thickness in the Cu2O/CuO photocathode by controlling the annealing time: optimal thickness of CuO induces the improved light utilization and band bending, resulting in the enhanced photoelectrochemical performance.

No abstract

The authors report high-temperature stable, spectrally tunable, Pt/alumina hyperbolic metafilms with broadband absorption. Two uniform pairs of Pt (10 nm)/alumina (100, 150, or 200 nm) multilayer films with a top alumina passivation layer and a bottom Pt mirror and are prepared on sapphire substrates by sputtering. These Pt/alumina multilayer films yielded strong light absorption at visible to near-infrared wavelengths that are spectrally tunable by modulating the thickness of each alumina layer. Based on effective medium theory for 1D metafilms, such tuning behavior is well understood; the maximum absorption occurred at a specific range of wavelengths wherein the real part of the effective permittivity was near-zero. The broadband absorption spectrum is only marginally altered over a wide range of incident angles from 0 to 70 , a finding supported by simulations using the transfer matrix method using the experimentally derived optical constants of Pt and alumina. The fabricated Pt/alumina multilayer films maintained their initial absorption spectra after a heating test at 1450 K for 12 h. Transmission electron microscopy images and fast Fourier transform diffraction patterns show pristine Pt/alumina interfaces, devoid of any features related to oxidation, interdiffusion, and deformation after the heating test. These pristine interfaces are further verified with the elemental mapping results obtained by energy dispersion X-ray spectroscopy. This work demonstrates that a one-dimensional stack of Pt and alumina layers with deep-submicron thicknesses functions as a refractory hyperbolic metamaterial with a large absorption at specific wavelengths, which will be extensively utilized in a diverse range of thermal radiation-engineered applications.

No abstract

Nickel phosphide (Ni-P) films as a catalytic cathode for the hydrogen evolution reaction (HER) of a water splitting were fabricated by a pulse-reverse electrodeposition technique. The electrochemical behaviors for the electrodeposition of Ni-P were investigated by the characterization of peaks in a cyclic voltammogram. The composition of the electrodeposited Ni-P alloys was controlled by adjusting duty cycles of the pulse-reverse electrodeposition. The HER electrocatalytic properties of the Ni-P electrodeposits with an amorphous phase as a function of phosphorous contents existing in Ni-P were electrochemically characterized by the analysis of overpotentials, Tafel slopes, and electrochemical impedance spectrometry. Additionally, the elemental Ni-embedded crystalline Ni3P was prepared by an annealing process with the amorphous Ni69P31 electrodeposit with high contents of phosphorus. The crystalline structure with Ni inclusions in the matrix of Ni3P was formed by the precipitation of excess Ni. The electrocatalytic properties of crystalline Ni3P with elemental Ni inclusions were also investigated by electrochemical characterization.