RESUMEN
In this work, three dimensional (3D) self-supported Ni-FeOH@Ni-FeP needle arrays with core-shell heterojunction structure are fabricated via in situ hydroxide growth over Ni-FeP surface. The as-prepared electrodes show an outstanding oxygen evolution reaction (OER) performance, only requiring the low overpotential of 232 mV to reach 200 mA cm-2 with the Tafel slop of 40 mV dec-1. For overall water splitting, an alkaline electrolyzer with these electrodes only requires a cell voltage of 2.14 V to reach 1 A cm-2. Mechanistic investigations for such excellent electrocatalytic performances are utilized by in situ Raman spectroscopy in conjunction with density functional theory (DFT) calculations. The computation results present that Ni-FeOH@Ni-FeP attains better intrinsic conductivity and the D-band center (close to that of the ideal catalyst), thus giving superior excellent catalytic performances. Likewise, the surface Ni-FeOH layer can improve the structural stability of Ni-FeP cores and attenuate the eventual formation of irreversible FeOOH products. More importantly, the appearance of FeOOH intermediates can effectively decrease the energy barrier of NiOOH intermediates, and then rapidly accelerate the sluggish reaction dynamics, as well as further enhance the electrocatalytic activities, reversibility and cycling stability.
RESUMEN
We report a wavelength-tunable harmonically mode-locking dissipative soliton fiber laser based on a high-speed intensity modulator with a simple all-polarization-maintaining (all-PM) cavity. The center wavelength can be precisely tuned from 1029.35 to 1079.25 nm by tuning only the frequency of the pulse pattern generator (PPG), and the linear tuning accuracy of the wavelength can reach 0.0093 nm/kHz. The degree of polarization can reach 98.969%. The FWHM of the pulse is measured to be 30.1 ps, and the intracavity pulse energy after the gain fiber can reach 5.41 nJ. All orders of the harmonic mode-locking repetition rate are tuned from â¼33.346 to â¼366.806 MHz through adjustment of the data length and frequency of PPG.