Research on non-noble metal bifunctional electrocatalysts with high efficiency and long-lasting stability is crucial for many energy storage devices such as zinc-air batteries. In this report, ...nitrogen-doped porous hollow carbon spheres with a size of about 300 nm were fabricated using a modified Stöber method and decorated with an FeNi alloy through a pyrolytic reduction process, resulting in a promising bifunctional electrocatalyst for both the oxygen evolution reaction and oxygen reduction reaction. The as-prepared FeNi@NHCS electrocatalyst exhibits excellent bifunctional activity in KOH electrolyte, attributed to its mesoporous structure, large specific surface area, and the strong coupling between the FeNi nanoalloy and nitrogen-doped carbon carriers. The electrocatalyst demonstrates excellent ORR performance with
E
1/2
= 0.828 V and OER activity with
E
j
=10 mA
= 1.51 V. A zinc-air battery using FeNi@NHCS as the air electrode achieves an open-circuit voltage of 1.432 V and a maximum power density of 181.8 mW cm
−2
. After 300 h of galvanostatic charge-discharge cycles, the charge-discharge voltage gap (Δ
U
) of the battery had only decayed by 2.7%, demonstrating superior cycling stability.
The Zn-air battery assembled by the bifunctional FeNi@HMCS electrocatalyst displayed a maximum power density of 181.8 mW cm
−2
and superior stability for over 300 hours.
The use of transition metals as bifunctional catalysts for rechargeable zinc-air batteries has recently attracted much attention. Due to their multiple chemical valence states, the cobalt oxides are ...considered to be promising catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, bifunctional Ag-decorated Cosub.3 Osub.4 -nitrogen doped porous carbon composite (Cosub.3 Osub.4 -NC&Ag) catalysts were synthesized by annealing ZIF-67 in Nsub.2 and Osub.2 , respectively, followed by Ag deposition using chemical bath deposition. Due to the decoration of Ag nanoparticles and high specific surface area (46.9 msup.2 gsup.−1 ), the electrochemical activity of Cosub.3 Osub.4 increased significantly. The optimized Cosub.3 Osub.4 -NC&Ag catalysts possessed superior ORR performance with a half-wave potential of 0.84 V (vs. RHE) and OER activity with an overpotential of 349 mV at 10 mA cmsup.−2 . The open circuit voltage of the Cosub.3 Osub.4 -NC&Ag-based zinc-air battery was 1.423 V. Meanwhile, the power density reached 198 mW cmsup.−2 with a specific discharge capacity of 770 mAh gsup.−1 at 10 mA cmsup.−2 , which was higher than that of Pt/C-based zinc-air battery (160 mW cmsup.−2 and 705 mAh gsup.−1 ). At a current density of 10 mA cmsup.−2 , the charge-discharge performance was stable for 120 h (360 cycles), exhibiting better long-term stability than the Pt/C&RuOsub.2 counterpart.
The use of transition metals as bifunctional catalysts for rechargeable zinc-air batteries has recently attracted much attention. Due to their multiple chemical valence states, the cobalt oxides are ...considered to be promising catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, bifunctional Ag-decorated Co3O4-nitrogen doped porous carbon composite (Co3O4-NC&Ag) catalysts were synthesized by annealing ZIF-67 in N2 and O2, respectively, followed by Ag deposition using chemical bath deposition. Due to the decoration of Ag nanoparticles and high specific surface area (46.9 m2 g−1), the electrochemical activity of Co3O4 increased significantly. The optimized Co3O4-NC&Ag catalysts possessed superior ORR performance with a half-wave potential of 0.84 V (vs. RHE) and OER activity with an overpotential of 349 mV at 10 mA cm−2. The open circuit voltage of the Co3O4-NC&Ag-based zinc-air battery was 1.423 V. Meanwhile, the power density reached 198 mW cm−2 with a specific discharge capacity of 770 mAh g−1 at 10 mA cm−2, which was higher than that of Pt/C-based zinc-air battery (160 mW cm−2 and 705 mAh g−1). At a current density of 10 mA cm−2, the charge-discharge performance was stable for 120 h (360 cycles), exhibiting better long-term stability than the Pt/C&RuO2 counterpart.
Substrate-integrated waveguides (SIWs) have recently attracted increasing attention for the development of terahertz (THz) circuits and systems. However, conventional SIWs employ fixed metallic vias ...to form the waveguide sidewalls, resulting in limited tunability and reconfigurability. In this paper, we report a novel approach for the realization of high-performance tunable and/or reconfigurable THz SIW structures. In this approach, photo-induced free carriers are generated in a high-resistivity silicon pillar-array structure to form well-defined, highly conductive, vertical sidewalls. The wave propagation properties of these optically-defined photo-induced SIWs (PI-SIWs) have been evaluated using full-wave electromagnetic simulations. Higher-functionality THz components, including a single-pole double-throw switch and a phase shifter were also designed and simulated. Based on these example circuits, PI-SIWs using pillar-array structures appear to be attractive candidates for the development of tunable and reconfigurable THz components for THz sensing, imaging, and communication systems.
A novel and cost-effective approach for high-resolution terahertz (THz) imaging using photoinduced (PI) coded-apertures on micromachined mesa-array structures is reported. The mesa-array structures ...are designed to have subwavelength electrically isolated mesas for generation of high-fidelity photopatterns for THz imaging. An Si mesa-array prototype structure was successfully fabricated and tested. Measurements show that a modulation depth of ∼22 dB was obtained in the frequency range of 740-750 GHz under a light intensity of 11.7 W/cm 2 , which agrees well with theoretical analysis and full-wave simulation. Initial imaging experiments were first performed using 64 pixels (over different areas) for validation and performance evaluation. More advanced imaging using quadrupled pixel number (256 pixels) was conducted in order to resolve subwavelength features. As a result, a wavelength-scale spatial resolution of 400 μm has been successfully demonstrated, and a subwavelength resolution as small as ∼250 μm (0.625 λ at 740 GHz) has been shown to be potentially achievable. The proposed PI coded-aperture imaging using mesa arrays is promising for developing real-time high-resolution THz imaging with simple system and low cost.
We report a novel approach for achieving subwavelength terahertz (THz) imaging using photo-induced coded apertures on mesa-array structures. The structure facilitates the generation of ...high-resolution photopatterns by confining photo-induced free carriers inside isolated mesas. Such mesa-array structures were successfully fabricated on Si substrates. Measurement shows that an average modulation depth of ~20 dB over the frequency range of 500-750 GHz has been achieved using the mesa-array under a light intensity of ~11.7 W/cm 2 , which agrees well with theoretical analysis and fullwave simulation. For prototype imaging demonstrations, a set of objects were successfully imaged at 740 GHz over different areas, and the initial results indicate that a ~438 µm imaging resolution was achieved. The coded-aperture imaging using mesa-arrays is promising for extension to subwavelength imaging for applications in high-performance THz imaging systems.
We report a novel high-performance terahertz (THz) switch using photoconductivity modulation. By using a Ge or Si thin film capacitively coupled across a coplanar waveguide (CPW), a non-contact shunt ...switch configuration offering extremely low insertion loss and superior isolation at THz frequencies can be achieved. Physics-based modeling and HFSS full wave simulation from 110-220 GHz for a Ge-based switch show that an insertion loss (IL)<0.3 dB and isolation (Iso)>70 dB can be achieved with an illumination light intensity of 100 W/cm 2 . As a prototype to validate the approach, a micromachined Si chip of 73 μm thickness was mounted on top of D- and G-band CPWs on alumina substrates. To control the switch, an 808 nm wavelength fiber-coupled laser diode was used for illumination. On-wafer measurements over D- and G-bands agree with the simulations. At 170 GHz, the measured on-state IL was 0.4 dB, and the off-state isolation exceeded 32 dB. This outperforms most reported THz switches, across a range of technologies. The proposed THz switching is promising for developing high performance reconfigurable circuits required for more advanced THz sensing, imaging and communication applications.
A novel design of wideband filtering power divider (FPD) with high selectivity, good isolation and widen upper stopband is presented in this paper. A new topology is proposed by adding an isolation ...resistor between two tri-mode resonators to guarantee the isolation. Besides, owing to the intrinsic characteristics of tri-mode resonators and coupled lines with one of them terminated by an open-circuited stub, four transmission zeros (TZs) can be generated outside the operating band to improve the signal selectivity. For demonstration, a FPD operating at 2.35 GHz with 3-dB fractional bandwidth of 25.6% is designed, fabricated and measured. The measured isolation is better than 15.5 dB and the upper stopband is extended to 7.6 GHz (3.23f0) with a rejection level of 20 dB.
![Ag Decorated Co[sub.3]O[sub...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2071-1050/small "Ag Decorated Co[sub.3]O[sub.4]-Nitrogen Doped Porous Carbon as the Bifunctional Cathodic Catalysts for Rechargeable Zinc-Air Batteries")
PDF
