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.

The critical role of the thicknesses of the top and bottom oxide layers, as well as Ag layer, in ZnO/ Ag/ZnO transparent conductive electrodes were investigated. The Ag forms a nearly continuous layer at the thickness of 8 nm, at which the Ag sheet resistance of 8.0 Ω/Sq. is lower than the typical criteria of 10 Ω/ Sq. By making independent changes in the thickness of the top and bottom ZnO layers, which serve as antireflection layers, it was found that the top ZnO layer thickness has a dominant impact, with the bottom ZnO layer thickness contributing a less but still significant amount. The optimized thicknesses for the top and bottom ZnO layers were found to be 40 and 20-30 nm, respectively, resulting in a peak transmittance of 97.1% and average visible light transmittance of 90.8%. According to the Haccke figure of merit ( ), the value for the optimized ZnO/Ag/ZnO electrode was 0.048, which is highly competitive for transparent conductive electrodes for future optoelectronic devices.

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.