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Petal-like ultra-evenly Rh-doped Co2Fe-P composite was fabricated by a solvothermal and in-situ phosphorization strategy. Through doping a small amount of Rh within the Co2Fe-P structure, the catalytic activities of the composite for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) could be highly improved, and an excellent electrochemical bifunctional catalyst could be achieved. Under acidic reaction conditions, it only required an overpotential of 76 mV for HER to achieve a current density of 10 mA·cm−2. Meanwhile, excellent electrochemical performance could also be obtained in alkaline electrolytes. The overpotential was 48 mV for HER and 303 mV for OER at 10 mA·cm−2 in 1 M KOH, respectively. Impressively, as a bifunctional electrode, the Rh doped Co2Fe-P composite can release a current density of 10 mA·cm−2 at a low cell voltage of 1.54 V in 1 M KOH for overall water splitting, which could be compared with that using commercial noble metal catalysts.

This study presents a novel planar coupled-line directional coupler with tunable both power division ratio and operating frequency, which is achieved using microstrip technology for the first time. Its tunability of the operating frequency and the power division ratio, or coupling ratio, can be independently controlled by the bias voltages. Moreover, it can simultaneously maintain perfect port match and isolation. On the basis of the even–odd mode analysis method, both the closed-form analytical equations and parameter discussions are provided to facilitate the practical design. An experimental prototype of the tunable coupler is simulated, fabricated, and measured to demonstrate how it works. The measured results indicate that power division ratio can vary from 0.35 (9 dB) to 0.71 (3 dB) when operating frequency ranges from 0.55 to 1.48 GHz (91.63%) while power division ratio varies from 0.35 (9 dB) to 1 (0 dB) when operating frequency is fixed at 1 GHz, which validated the reliability of the proposed model.

In this paper, a novel coupled-line tunable Wilkinson power divider with perfect port match and isolation in a continuously tunable passband is presented. The proposed tunable power divider consists of an isolation resistor, two coupled lines, and two types of varactors. By providing these varactors with suitable bias voltages, the operating frequency of the proposed power divider can be flexibly changed as desired. Meanwhile, perfect port match and isolation are maintained at all tunable operating frequencies. After applying the even-odd mode analysis method, the closed-form equations of the design parameters are derived to illuminate the effects on the minimum and maximum operating frequencies. These equations exhibit that the proposed power divider has a wide frequency tuning range and a high tunability (more than 110% in ideal conditions). Owing to the limitation of manufacturing process, a microstrip power divider with a tunable frequency of 0.54–1.41 GHz (89.23%) is designed and simulated based on the provided closed-form equations. The measured results show a frequency tuning range from 0.56 to 1.39 GHz (85.13%) with a more than 20-dB return loss and isolation in the entire tuning range, agreeing well with the simulation results.

In this paper, a novel compact tunable coupled-line power divider using varactors is presented. It has a compact circuit due to the coupled line with short electrical length. The operating frequency can be flexibly controlled by the bias voltage because the capacitance of the varactors is regulated by the applied bias voltage. The theory of this power divider is analyzed and a microstrip example of this tunable power divider is designed, fabricated, and measured. The measured results indicate that the operating frequency of the proposed tunable power divider ranges from 0.8 to 1.15 GHz, agreeing well with the simulated result.