Remedy for Collapse of ZIF Derived Carbon: Micro-Pore Filled Synthesis to Improve ORR Catalytic Property

Zeolitic imidazolate framework (ZIF) derived carbons deliver outstanding performance as oxygen reduction reaction (ORR) catalysts. However, their electrocatalytic activities are limited due to unavoidable collapse of ZIFs upon pyrolysis, which results in degradation of porosity, sintering of metals and loss of active sites. In this work, a micro-pore filling strategy was employed to strength the architecture of ZIF by using size matched cyanamide molecules as fillers. The cyanamide with high nitrogen content shows a triple effect in stabilizing the carbonaceous skeleton, preserving of metal containing active sites and improving the conductivity of matrix. Therefore, the as-prepared Fe, Co co-doped ZIF derived carbon (FeCo@NC-N) delivers a significantly improved electrochemical activity for ORR than its unfilled counterpart, with half-wave potential upshifted by 30 mV (0.84 V vs. RHE). Besides, a promoted power density of home-assembled zinc-air battery is obtained when FeCo@NC-N is applied as cathode catalyst. This work demonstrates a reliable approach to mitigate framework collapse of metal organic framework (MOF), thus may open a new way for fabrication of MOF based catalysts with increased loading of pores and active sites.

Engineering Mn Atomic Sites in Multi-Dimensional Nitrogen-Doped Carbon for Highly Efficient Oxygen Reduction Reaction

Nitrogen-coordinated single-atom manganese in multi-dimensional nitrogen-doped carbon electrocatalysts (Mn-NC) was successful constructed by combing two-dimensional nanosheets and one-dimensional nanofibers. The Mn-NC exhibited excellent oxygen reduction reaction catalytic activity with half-wave...

Coordinated Co-NC/CoFe Dual Active Centre Embedded Three-dimensional Ordered Macroporous Framework as Bifunctional Catalyst for Efficient and Stable Zinc-Air Batteries

Developing efficient and stable multifunctional electrocatalyst is very important for zinc-air batteries in practical. Herein, semiconductive spinel CuFe2O4 supported Co-N co-doped carbon (Co-NC) and CoFe alloy nanoparticles were proposed. In this strategy, the three-dimensional ordered macroporous CuFe2O4 support provides rich channels for mass transmission, revealling good corrosion resistance and durability at the same time. ZIF-67 derived Co-NC decoration improves the conductivity of the catalyst. Further, the uniformlydistributed Co-NC and CoFe nanoparticles (C/CF) dramatically promote the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance. Accordingly, C/CF@CuFe2O4 catalyst shows remarkable bifunctional electrocatalytic activity, with an ORR half-wave potential of 0.86 V, and an OER over-potential of 0.46 V at 10 mA cm-2. The zinc-air battery using this catalyst exhibits a power density of 95.5 mW cm-2 and a durable cyclability for over 170 h at a current density of 10 mA cm-2, which implies a great potential in practical application.

N, S, P-Codoped Graphene-Supported Ag-MnFe2O4 Heterojunction Nanoparticles as Bifunctional Oxygen Electrocatalyst with High Efficiency

Due to slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharging and charging processes, it is essential to rationally design and synthesize non-precious metal bifunctional electrocatalysts with good performance for metal-air batteries. Herein, Ag-MnFe2O4 heterojunction nanoparticles supported on N, S, P-codoped graphene (NSPG) are developed with enhanced ORR and OER bifunctional electrocatalytic activities and stability. In contrast, S, P-doped graphene (SPG) and N, P-doped graphene (NPG) show less stabilization for the heterojunction particles. For example, under alkaline conditions, the ORR half-wave potential of Ag-MnFe2O4/NSPG can reach 0.831 V, and the over potential for OER is 0.56 V at the current density 10 mA·cm−2. Furthermore, Ag-MnFe2O4/NSPG shows better methanol resistance and durability than Pt/C catalysts.

Embedding Co2P nanoparticles in Cu doping carbon fibers for Zn-Air batteries and supercapacitors

Developing highly efficient and non-precious materials for Zn-air batteries (ZABs) and supercapacitors (SCs) are still crucial and challenging. Herein, electronic reconfiguration and introducing conductive carbon-based materials are simultaneously conducted to enhance the ZABs and SCs performance of Co2P. We develop a simple and efficient electrospinning technology followed by carbonization process to synthesize embedding Co2P nanoparticles in Cu doping carbon nanofibers (Cu-Co2P/CNFs). As a result, the 7% Cu-Co2P/CNFs presents high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. (half-wave potential of 0.792 V for ORR, overpotential of 360 mV at 10 mA cm-2 for OER). ZABs that employed 7% Cu-Co2P/CNFs and acetylene black at a mass ratio of 1:2 as the cathode electrocatalyst exhibit a power density of 230 mW cm-2 and excellent discharge-charge reversibility of 80 h. In addition, the 7% Cu-Co2P/CNFs show the specific capacitance of 558 F g-1 at 1 A g-1. Moreover, the asymmetric supercapacitor (ASC) is assembled applying 7% Cu-Co2P/CNFs electrode and pure CNFs, which exhibits a high energy density (25.9 Wh kg-1), exceptional power density (217.5 kW kg-1) and excellent cycle stability (96.6% retention after 10,000 cycles). This work may provide an effective way to prepared Co2P based materials for ZABs and SCs applications.

Compact and High-Efficiency Rectenna for Wireless Power-Harvesting Applications

A compact, single-layer microstrip rectenna for dedicated far-field RF wireless power-harvesting applications is presented. The proposed rectenna circuit configurations including multiband triple L-Arms patch antenna with diamond slot ground are designed to resonate at 10, 13, 17, and 26 GHz with 10 dB impedance bandwidths of 0.67, 0.8, 2.45, and 4.3 GHz, respectively. Two rectifier designs have been fabricated and compared, a half wave rectifier with a shunted Schottky diode and a voltage doubler rectifier. The measured and simulated maximum conversion efficiencies of the rectifier using the shunted diode half-wave rectifier are 41%, and 34%, respectively, for 300 Ω load resistance, whereas they amount to 50% and 43%, respectively, for voltage doubler rectifier with 650 Ω load resistance. Compared to the shunted rectifier circuit, it is significant to note that the voltage doubler rectifier circuit has higher efficiency. Both rectifier’s circuits presented are tuned for a center frequency of 10 GHz and implemented using 0.81 mm thick Rogers (RO4003c) substrate. The overall size of the antenna is 16.5 × 16.5 mm2, and the shunted rectifier is only 13.3 × 8.2 mm2 and 19.7 × 7.4 mm2 for the voltage doubler rectifier. The antenna is designed and simulated using the CST Microwave Studio Suite (Computer Simulation Technology), while the complete rectenna is simulated using Agilent’s ADS tool with good agreement for both simulation and measurements.

Active control of a sandwich plate with reinforced magnetostrictive faces and viscoelastic core, resting on elastic foundation

The current study presents a vibration investigation of a laminated plate considering a viscoelastic core with embedded magnetostrictive layers. The simply-supported plate is supported via Pasternak’s substrate medium. Based on different plate theories and employing Hamilton’s principle, the system of governing differential equations is derived. The mechanical properties of the viscoelastic core are described depend on the time varies based on Kelvin–Voigt model. Actuating magnetostrictive layers are utilized to control the vibration damping process of the system with the assistance of feedback and constant gain distributed control. The analytical solution is obtained to investigate the influence of half wave numbers, thickness ratios, core thickness, aspect ratios, lamination schemes, elastic foundation parameters, damping coefficient, feedback coefficient magnitude, magnetostrictive layers location, on the vibrational behavior of laminated plate. Some observations about the vibration damping process of the present plate are displayed. The results refer to that the vibration suppression rate depends on the thickness of the plate, the feedback control value, the foundation constants, and the viscoelastic structural damping significantly. Moreover, the study can be providing benchmark tests to validate future contributions on the viscoelastic smart structural issues and developing the design of smart viscoelastic structures and control of their vibrations.