Vanadium-doped Ni microspheres loaded with phosphatization of NiMoO4 contributing to enhanced electron transfer for stable overall water splitting.

At present, there are few reports on the micron-sized catalysts for overall water splitting. In this study, phosphating method were used to construct the self-supporting catalyst (V doped Ni microspheres coated by NiMoO4/Ni12P5) with microspherical structure, providing a short path and a stable structure to guarantee quick electron transfer and excellent catalytic performance. Hence, oxygen evolution reaction (OER) only needs 254 mV to reach a current density of 50 mA cm-2 in 1.0 mol/L KOH, after 114 h without attenuation. The catalyst can achieve a current densitiy of 10 mA cm-2 with a voltage of only 158 mV for hydrogen evolution reaction (HER). When micron scale V-Ni@NiMoO4/Ni12P5 is used as both anode and cathode for overall water splitting, the device can operate at a current density of 10 mA cm-2 for more than 200 h of good stability. Its superior catalytic performance can be attributed to the construction of micron size and phosphating. DFT calculations indicate that the introduction of P better activates the adsorbed *OH and H2O*, reduces reaction the energy barrier, and improves the catalytic activity.

CeO2 for modulating the electronic structure of nickel-cobalt bimetallic phosphides to promote efficient overall water splitting.

The discovery of earth-abundant electrocatalysts to replace platinum and iridium for overall water splitting is a crucial step in reducing the cost of green hydrogen production. Transition metal phosphides have drawn wide attention due to their non-toxicity, good chemical stability, low cost, and stable catalytic activity in alkaline electrolytes. We report a three-dimensional flower-like structure composed of core-shell nanoneedles as catalysts, in which CeO2 is introduced on the surface of nickel cobalt bimetallic phosphide through electrodeposition. And X-ray photoelectron spectroscopy testing and DFT calculations show electron coupling and transfer between CeO2 and CoP3, thereby modulating the electronic structure of the catalyst surface and reducing the adsorption energy of H atoms during the catalytic process, resulting in enhanced catalytic activity. In 1 M KOH, it exhibits a low overpotential of 109 and 296 mV to achieve the current density of 50 mA cm-2 for HER and OER, respectively. When used as both cathode and anode as a bifunctional catalyst, a voltage of only 1.77 V is required to achieve a current density of 50 mA cm-2, demonstrating great industrial potential.

Tunable triangular frequency modulated microwave waveform generation with improved linearity using an optically injected semiconductor laser.

A photonic approach to generating a triangular frequency modulated microwave waveform with improved linearity using an optically injected semiconductor laser is proposed and demonstrated. By controlling the optical injection strength to the semiconductor laser at the period-one oscillation state to have a triangular shape, a triangular frequency modulated microwave waveform is generated after the optical-electrical conversion. A method based on a generalized regression neural network is proposed to improve the linearity of the generated waveform. By adjusting the parameters of the low-frequency electrical triangular control signal, the tunability of the center frequency, bandwidth, and time duration of the generated waveform can be realized. In the proof-of-concept experiment, a triangular frequency modulated microwave waveform with a frequency range from 14-24 GHz and a time duration of 2 µs has been successfully generated. The improvement of the linearity of the waveform is experimentally verified. The performance of the generated triangular frequency modulated microwave waveforms for reducing the range-Doppler coupling is verified through the analyses of the ambiguity function. The tunability of the center frequency, bandwidth, and time duration is also experimentally demonstrated.

Microwave channelizer based on a photonic dual-output image-reject mixer.

A microwave channelizer based on a photonic dual-output image-reject mixer (IRM) is proposed and demonstrated. By introducing the dual-output IRM based on the balanced Hartley structure, 2N channels can be produced by using the optical frequency combs (OFCs) with N comb lines. The required electrical hybrids and the optical filters are also reduced by half. In addition, the channelization efficiency is doubled, and the in-band interferences, including the image and the nonlinear mixing spurs, are greatly suppressed. A proof-of-concept experiment is performed. By applying a pair of OFCs with three comb lines, an RF signal with a 6 GHz instantaneous bandwidth is successfully divided into six channels with 1 GHz bandwidth. The in-band interference is suppressed by more than 25 dB for all channels.

Photonics-based reconfigurable multi-band linearly frequency-modulated signal generation.

A photonics-based multi-band linearly frequency-modulated (LFM) waveform generator with reconfigurable center frequency, bandwidth and time duration is proposed and demonstrated. By introducing two coherent optical frequency combs (OFCs) with a frequency shift and different free spectral ranges (FSRs) as multi-frequency optical LOs, a set of LFM signals with different center frequencies will be generated if one of the combs is modulated by an intermediate-frequency (IF) LFM signal. The center frequencies of the generated RF-LFM signals can be flexibly tuned by adjusting the frequency shift between the two OFCs. In addition, by introducing a series of proper time delays to the LFM signals and combining them, a frequency-stepped LFM signal can be generated. Furthermore, when the bandwidth of the IF-LFM signal equals the difference of the comb FSRs, and the time duration of IF-LFM signal equals the time delay of the consecutive channels, a LFM signal with both bandwidth and time duration multiplied can be obtained. With N comb lines, the maximum achievable time-bandwidth product (TBWP) is N × N times of the applied IF LFM signal. A proof-of-concept experiment is carried out. A set of LFM signals with frequencies ranging from L to Ka bands are generated. By introducing proper time delays, a frequency-stepped LFM signal with frequency steps between 10 GHz and 20 GHz is also produced. In addition, LFM signals with the bandwidth and time duration multiplied by 2 and 5 are realized (4-GHz bandwidth, 2-µs time duration and 10-GHz bandwidth, 5-µs time duration), respectively. Correspondingly, the TBWPs are increased by 4 and 25 times.