High Peak Power Density Research Articles

Nitrogen‐Rich Rigid Polybenzimidazole With Phosphoric Acid Shows Promising Electrochemical Activity and Stability for High‐Temperature Proton Exchange Membrane Fuel Cells

AbstractPolybenzimidazoles (PBIs) are the most promising binders for the catalyst layer (CL) in high‐temperature proton exchange membrane fuel cells (HT‐PEMFC). However, traditional commercial PBIs are not applied in binders because they do not enhance the electrochemical performance and because the related solvents are not environmentally friendly. In addition, proton transfer channels in PBIs are not investigated at the microscopic and atomic scales to date. In this study, a nitrogen‐rich rigid PBI binder containing pyridine, diazofluorene, and partially grafted nitrile (PBPBI‐3CN) is prepared with a functionalized structure, good thermal stability, and good solubility in an environmentally friendly solvent. A membrane electrode assembly (MEA) is fabricated with the PBPBI‐3CN binder, providing a high peak power density, low resistance, and good stability. The protonation, hydrogen bond networks, and platform for proton transfer are confirmed in the CLs. The protonation of PBPBI‐3CN occurs in two steps. First, some phosphoric acid (PA) molecules bind to nitrogen‐containing acidophilic groups via preliminary protonation; second, multiple PA molecules then interact with nitrogen‐containing acidophilic groups via further protonation. With protonation as the foundation, a sufficient amount of PA molecules form a hydrogen bond network, and proton transfer channels are established.

Microlens array device for laser light shaping in laser scanning smart headlights.

We present, what we believe to be, a novel microlens array (MLA) scheme for laser light shaping in laser scanning smart headlight. The laser spot has a Gaussian distribution that may reach a high peak power density in the central part, which is called hot spot. When the laser beam is applied to a phosphor plate for luminous conversion, the hot spot of Gaussian beam causes thermal quench and decreases luminous efficacy. To avoid this effect, an MLA is used, so as to achieve a uniform energy distribution. In this study, we propose a laser scanning smart headlight fabricated by a new MLA structure, with an arrangement providing both light uniformity and shaping. The novel MLA is designed by two-dimensional micro-concave lens array yielding a flat-top beam. The flexible fabrication process employs laser drilling to shape the micro-hole array on the glass substrate surface and then etch it to form MLA without requiring any mask lithography process. The full-width half maximum (FWHM) of light output distribution can be adjusted by the glass etching parameters, and the light distribution could be controlled by the arranged layout of the array. Thus, beams with FWHM divergence ranging from 5° to 34° has been fabricated and characterized. The typical pixel shape is a rectangle with two different FWHMs in two orthogonal directions, and the fabrication method achieves this goal as well. This novel design and unique maskless process of the MLAs is a promising tool for development the next generation laser scanning smart headlight.

Covalent organic framework-derived fluorine, nitrogen dual-doped carbon as metal-free bifunctional oxygen electrocatalysts

The construction of heteroatom-doped metal-free carbon catalysts with bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired for Zn-air batteries, but remains a great challenge owing to the sluggish kinetics of OER and ORR. Herein, a self-sacrificing template engineering strategy was employed to fabricate fluorine (F), nitrogen (N) co-doped porous carbon (F-NPC) catalyst by direct pyrolysis of F, N containing covalent organic framework (F-COF). The predesigned F and N elements were integrated into the skeletons of COF precursor, thus achieving uniformly distributed heteroatom active sites. The introduction of F is beneficial for the formation of edge-defects, contributing to the enhancement of the electrocatalytic activity. Attributing to the porous feature, abundant defect sites induced by F doping, as well as the strong synergistic effect between N and F atoms to afford a high intrinsic catalytic activity, the resulting F-NPC catalyst exhibits excellent bifunctional catalytic activities for both ORR and OER in alkaline mediums. Furthermore, the assembled Zn-air battery with F-NPC catalyst shows a high peak power density of 206.3 mW cm−2 and great stability, surpassing the commercial Pt/C + RuO2 catalysts.

Hierarchically Porous Carbons with Highly Curved Surfaces for Hosting Single Metal FeN4 Sites as Outstanding Oxygen Reduction Catalysts.

Iron-nitrogen-carbon (FeNC) materials have emerged as a promising alternative to platinum-group metals for catalyzing the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells. However, their low intrinsic activity and stability are major impediments. Herein, an FeN-C electrocatalyst with dense FeN4 sites on hierarchically porous carbons with highly curved surfaces (denoted as FeN4 -hcC) is reported. The FeN4 -hcC catalyst displays exceptional ORR activity in acidic media, with a high half-wave potential of 0.85V (versus reversible hydrogen electrode) in 0.5m H2 SO4 . When integrated into a membrane electrode assembly, the corresponding cathode displays a high maximum peak power density of 0.592W cm-2 and demonstrates operating durability over 30000 cycles under harsh H2 /air conditions, outperforming previously reported Fe-NC electrocatalysts. These experimental and theoretical studies suggest that the curved carbon support fine-tunes the local coordination environment, lowers the energies of the Fe d-band centers, and inhibits the adsorption of oxygenated species, which can enhance the ORR activity and stability. This work provides new insight into the carbon nanostructure-activity correlation for ORR catalysis. It also offers a new approach to designing advanced single-metal-site catalysts for energy-conversion applications.

Contracted Fe-N5-C11 Sites in Single-Atom Catalysts Boosting Catalytic Performance for Oxygen Reduction Reaction.

Promoting the catalyst performance for oxygen reduction reaction (ORR) in energy conversion devices through controlled manipulation of the structure of catalytic active sites has been a major challenge. In this work, we prepared Fe-N-C single-atom catalysts (SACs) with Fe-N5 active sites and found that the catalytic activity of the catalyst with shrinkable Fe-N5-C11 sites for ORR was significantly improved compared with the catalyst bearing normal Fe-N5-C12 sites. The catalyst C@PVI-(TPC)Fe-800, prepared by pyrolyzing an axial-imidazole-coordinated iron corrole precursor, exhibited positive shifted half-wave potential (E1/2 = 0.89 V vs RHE) and higher peak power density (Pmax = 129 mW/cm2) than the iron porphyrin-derived counterpart C@PVI-(TPP)Fe-800 (E1/2 = 0.81 V, Pmax = 110 mW/cm2) in 0.1 M KOH electrolyte and Zn-air batteries, respectively. X-ray absorption spectroscopy (XAS) analysis of C@PVI-(TPC)Fe-800 revealed a contracted Fe-N5-C11 structure with iron in a higher oxidation state than the porphyrin-derived Fe-N5-C12 counterpart. Density functional theory (DFT) calculations demonstrated that C@PVI-(TPC)Fe-800 possesses a higher HOMO energy level than C@PVI-(TPP)Fe-800, which can increase its electron-donating ability and thus help achieve enhanced O2 adsorption as well as O-O bond activation. This work provides a new approach to tune the active site structure of SACs with unique contracted Fe-N5-C11 sites that remarkably promote the catalyst performance, suggesting significant implications for catalyst design in energy conversion devices.

Durable and High-Performance Thin-Film BHYb-Coated BZCYYb Bilayer Electrolytes for Proton-Conducting Reversible Solid Oxide Cells.

Proton-conducting reversible solid oxide cells are a promising technology for efficient conversion between electricity and chemical fuels, making them well-suited for the deployment of renewable energies and load leveling. However, state-of-the-art proton conductors are limited by an inherent trade-off between conductivity and stability. The bilayer electrolyte design bypasses this limitation by combining a highly conductive electrolyte backbone (e.g., BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb1711)) with a highly stable protection layer (e.g., BaHf0.8Yb0.2O3-δ (BHYb82)). Here, a BHYb82-BZCYYb1711 bilayer electrolyte is developed, which dramatically enhances the chemical stability while maintaining high electrochemical performance. The dense and epitaxial BHYb82 protection layer effectively protects the BZCYYb1711 from degradation in contaminating atmospheres such as high concentrations of steam and CO2. When exposed to CO2 (3% H2O), the bilayer cell degrades at a rate of 0.4 to 1.1%/1000 h, which is much lower than the unmodified cells at 5.1 to 7.0%. The optimized BHYb82 thin-film coating adds negligible resistance to the BZCYYb1711 electrolyte while providing a greatly enhanced chemical stability. Bilayer-based single cells demonstrated state-of-the-art electrochemical performance, with a high peak power density of 1.22 W cm-2 in the fuel cell mode and -1.86 A cm-2 at 1.3 V in the electrolysis mode at 600 °C, while demonstrating excellent long-term stability.

Construction of Co4 Atomic Clusters to Enable Fe-N4 Motifs with Highly Active and Durable Oxygen Reduction Performance.

Fe-N-C catalysts with single-atom Fe-N4 configurations are highly needed owing to the high activity for oxygen reduction reaction (ORR). However, the limited intrinsic activity and dissatisfactory durability have significantly restrained the practical application of proton-exchange membrane fuel cells (PEMFCs). Here, we demonstrate that constructing adjacent metal atomic clusters (ACs) is effective in boosting the ORR performance and stability of Fe-N4 catalysts. The integration of Fe-N4 configurations with highly uniform Co4 ACs on the N-doped carbon substrate (Co4 @/Fe1 @NC) is realized through a "pre-constrained" strategy using Co4 molecular clusters and Fe(acac)3 implanted carbon precursors. The as-developed Co4 @/Fe1 @NC catalyst exhibits excellent ORR activity with a half-wave potential (E1/2 ) of 0.835 V vs. RHE in acidic media and a high peak power density of 840 mW cm-2 in a H2 -O2 fuel cell test. First-principles calculations further clarify the ORR catalytic mechanism on the identified Fe-N4 that modified with Co4 ACs. This work provides a viable strategy for precisely establishing atomically dispersed polymetallic centers catalysts for efficient energy-related catalysis.

Construction of Co4 Atomic Clusters to Enable Fe−N4 Motifs with Highly Active and Durable Oxygen Reduction Performance

AbstractFe−N−C catalysts with single‐atom Fe−N4 configurations are highly needed owing to the high activity for oxygen reduction reaction (ORR). However, the limited intrinsic activity and dissatisfactory durability have significantly restrained the practical application of proton‐exchange membrane fuel cells (PEMFCs). Here, we demonstrate that constructing adjacent metal atomic clusters (ACs) is effective in boosting the ORR performance and stability of Fe−N4 catalysts. The integration of Fe−N4 configurations with highly uniform Co4 ACs on the N‐doped carbon substrate (Co4@/Fe1@NC) is realized through a “pre‐constrained” strategy using Co4 molecular clusters and Fe(acac)3 implanted carbon precursors. The as‐developed Co4@/Fe1@NC catalyst exhibits excellent ORR activity with a half‐wave potential (E1/2) of 0.835 V vs. RHE in acidic media and a high peak power density of 840 mW cm−2 in a H2−O2 fuel cell test. First‐principles calculations further clarify the ORR catalytic mechanism on the identified Fe−N4 that modified with Co4 ACs. This work provides a viable strategy for precisely establishing atomically dispersed polymetallic centers catalysts for efficient energy‐related catalysis.

MOF–Derived N–Doped C @ CoO/MoC Heterojunction Composite for Efficient Oxygen Reduction Reaction and Long-Life Zn–Air Battery

The high activity and reliability of bifunctional oxygen catalysts are imperative for rechargeable metal–air batteries. However, the preparation of bifunctional non–noble metal electrocatalysts with multiple active sites remains a great challenge. Herein, an MOF–derived N–doped C–loaded uniformly dispersed CoO/MoC heterojunction catalyst for high–performance dual function was prepared by a simple “codeposition–pyrolysis” method. Experimental investigations revealed that the formation of the heterojunction can tailor the valence of Co and Mo sites, which impressively modulates the electronic properties of the active sites and promotes the electrocatalytic processes. The optimal catalyst reveals a high–wave half potential (E1/2 = 0.841 V) for ORR and a low overpotential (E10 = 348 mV) for OER. The NCCM–600–based Zn–air battery displays a high peak power density of 133.36 mW cm−2 and a prolonged cycling life of more than 650 h. This work provides avenues for the development of functional materials with enhanced properties in a variety of practical energy applications.

Compact Design of 40 kV 100 A High-Voltage Pulsed-Power Modulator for Driving X-Band Magnetrons

This paper describes the design of a very compact high voltage pulsed power modulator for application in a medical linear accelerator (LINAC). This modulator is manufactured with a modular cell structure based on a semiconductor switch, and the heat dissipation structure is minimized through a simple and efficient charge-and-discharge circuit design. In addition, an equalized charging strategy for multiple capacitors and a high voltage electric field noise reduction strategy were applied. Thus, a high voltage pulsed-power modulator with a very compact size (310 (W) mm × 480 (H) mm × 230 (D) mm) and a high peak power density of 111 kW/L was realized without the use of an external cooling device such as a chiller. The modulator was built and experiments were conducted on high-voltage non-inductive resistive load outputs. The results show that the modulator had-a stable pulse voltage under various conditions, such as an output voltage of up to -40 kV, an output current of up to 100 A, a variable pulse width of 2∼10 μs, and an output repetition rate of up to 1 kHz. In addition, the high-voltage insulation reliability of the proposed modulator and its applicability to magnetron loads were verified.

A breakthrough in the performance and fuel utilization of methanol microfluidic fuel cell via viscous co-flow electrolyte

Microfluidic fuel cells (MFCs) employ laminar flows to eliminate the expensive polymer electrolyte membrane and overcome the various drawbacks caused by it. However, there is a trade-off between their electrochemical performance and fuel utilization, especially with methanol fuel due to its high diffusivity in water. Also, the power density and fuel utilization of existing methanol MFCs still need improvement. In this work, a MFC with an alkaline anolyte and acidic catholyte co-flow configuration was designed to achieve high open-circuit voltage and high power density. To better form a steady alkaline-acid co-flow interface and to suppress the methanol crossover, gelling polymers were added to increase the density and viscosity of the electrolytes. This reduced the flow rate required from hundreds to 25 μL min−1. In this manner, not only the trade-off was resolved, but also the peak power density and fuel utilization were prominently promoted. The highest peak power density was nearly 43.5 and 90 mW cm−2 at 25 and 100 μL min−1, respectively, and the fuel utilization per pass was 7.5 times higher compared with that in the literature. Moreover, the cell robustness was greatly improved because of the viscous co-flow configuration.

A General "In Situ Etch-Adsorption-Phosphatization" Strategy for the Fabrication of Metal Phosphides/Hollow Carbon Composite for High Performance Liquid/Flexible Zn-Air Batteries.

Benefiting from the admirable energy density (1086Whkg-1 ), overwhelming security, and low environmental impact, rechargeable zinc-air batteries (ZABs) are deemed to be attractive candidates for lithium-ion batteries. The exploration of novel oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts is the key to promoting the development of zinc-air batteries. Transitional metal phosphides (TMPs) especially Fe-based TMPs are deemed to be a rational type of catalyst, however, their catalytic performance still needs to be further improved. Considering Fe (heme) and Cu (copper terminal oxidases) are nature's options for ORR catalysis in many forms of life from bacteria to humans. Herein, a general "in situ etch-adsorption-phosphatization" strategy is designed for the fabrication of hollow FeP/Fe2 P/Cu3 P-N, P codoped carbon (FeP/Cu3 P-NPC) catalyst as the cathode of liquid and flexible ZABs. The liquid ZABs manifest a high peak power density of 158.5mWcm-2 and outstanding long-term cycling performance (≈1100 cycles at 2mAcm-2 ). Similarly, the flexible ZABs deliver superior cycling stability of 81h at 2mAcm-2 without bending and 26h with different bending angles.

NiCo alloy‐anchored self‐supporting carbon foam as a bifunctional oxygen electrode for rechargeable and flexible Zn–air batteries

AbstractThe design and fabrication of flexible, porous, conductive electrodes with customizable functions become the prime challenge in the development of new‐generation wearable electronics, especially for rechargeable batteries. Here, the NiCo bialloy particulate catalyst‐loaded self‐supporting carbon foam framework (NiCo@SCF) as a flexible electrode has been fabricated through one facile adsorption‐pyrolysis method using a commercial melamine foam. Compared with the electrode with Pt/C and Ir/C benchmark catalysts, the NiCo@SCF electrode exhibited superior bifunctional electrocatalytic performance in alkaline media with a half‐wave potential of 0.906 V for oxygen reduction reaction, an overpotential of 286 mV at j = 10 mA cm−2 for oxygen evolution reaction, and stable bifunctional performance with a small degradation after 20,000 voltammetric cycles. The as‐assembled aqueous zinc–air battery (ZAB) with NiCo@SCF as a self‐supporting air cathode demonstrated a high peak power density of 178.6 mW cm−2 at a current density of 10 mA cm−2 and a stable voltage gap of 0.94 V over a 540 h charge−discharge operation. Remarkably, the as‐assembled flexible solid‐state ZAB with self‐supporting NiCo@SCF as the air cathode presented an engaging peak power density of 80.1 mW cm−2 and excellent durability of 95 h undisrupted operation, showing promise for the design of wearable ZAB. The demonstrated electrode fabrication approach exemplifies a facile, large‐scale avenue toward functional electrodes, potentially extendable to other wearable electronics for broader applications.

Tailoring triple charge (O2−/H+/e−) conducting nature of Fe-based lanthanum doped samarium oxides for ceramic fuel cells (CFCs)

Lattice defects in rare earth (RE) doped single-phase semiconductor materials play a key role in structural modifications and physicochemical characteristics, resulting to enhance the ionic conductivity. In this work, we synthesized lanthanum doped samarium oxide with different mole ratios and applied it as a ceramics membrane fuel cell device to enable high peak power density (PPD) at low operational temperatures (520–400 °C). The samples are capable of triple charge H+/O2−/e− conduction and enhance the catalytic function of the cell in terms of HOR and ORR kinetics by producing lattice defects. The fabricated Sm1.5La1.5Fe5O12 (2-SLFO) fuel cell device exhibits a high OCV of 1.13 V with a maximum PPD of 864.26 mW/cm2 at 520 °C. Durability measurement verifies that 2-SLFO-based fuel cell device can be worked for 60 h under fuel cell conditions (H2/air) at 520 °C. The first principle calculations using density functional theory (DFT) demonstrate that the higher oxygen vacancy concentration in the 2-SLFO sample may cause to the higher charge-transfer kinetics, subsequent in the enhancement of ions transportation of the fabricated fuel cell device.

F‐Doped Co−N−C Catalysts for Enhancing the Oxygen Reduction Reaction in Zn‐Air Batteries

AbstractZn‐air battery is a promising next‐generation energy storage device. Its performance, however, is limited by a high overpotential resulted from the slow kinetics of the cathodic oxygen reduction reaction (ORR). This study reports a simple strategy for preparation of a fluorine‐doped Co−N−C composite as highly efficient electrocatalyst for ORR. The C@PVI‐(TPFC)Co‐800 catalyst was prepared by pyrolysis of F‐containing Co‐corrole that was assembled on PVI‐functionalized carbon black through the axial imidazole coordination (PVI=polyvinylimidazole, TPFC=5,10,15‐triperfluorophenyl‐21H, 22H‐corrole). The C@PVI‐(TPFC)Co‐800 catalyst exhibited much more positive ORR half‐wave potential (E1/2=0.88 V vs. RHE) than its counterpart C@PVI‐(TPC)Co‐800 (E1/2=0.82 V, TPC=5,10,15‐triphenyl‐21H, 22H‐corrole) without F‐doping in 0.1 M KOH electrolyte. C@PVI‐(TPFC)Co‐800 also achieved a greater kinetic current density and enhanced durability in alkaline media. In addition, a Zn‐air battery with C@PVI‐(TPFC)Co‐800 loaded at the cathode delivered much higher peak power density (Pmax=141 mW/cm2) and open‐circuit voltage (OCV=1.45 V) over the C@PVI‐(TPC)Co‐800 counterpart (Pmax=110 mW/cm2, OCV=1.39 V) and the commercial 20 % Pt/C (Pmax=119 mW/cm2, OCV=1.42 V) as well. The promoted catalyst performance for ORR was attributed to the increased specific surface area, more defects generated, and reduced electron density distribution around the Co metal center after F‐doping.

NaCl-assisted synthesis of 2D hexagonal FeNC nanosheets as efficient oxygen reduction catalyst for metal-air batteries

Iron coordinated with nitrogen (FeNx) sites hosted in the micropores of carbon substrate offer excellent performance for the oxygen reduction reaction (ORR). Achieving a highly exposed and dispersed FeNx sites accessible for ORR is still challenging to date. In this work, two-dimensional hexagonal carbon nanosheets supported FeNx moieties (FeNC-NaCl-T) were synthesized via a molten NaCl-assisted pyrolysis strategy. Benefit from the high specific surface area (1371.635 m3·g−1) and highly dispersed FeNx sites, the optimized FeNC-NaCl-900 exhibits superior ORR activity with a high half-wave potential of 0.90 V in alkaline electrolyte. Impressively, with FeNC-NaCl-900 as the cathode catalyst in aqueous zinc–air battery, achieving a remarkable performance with a high peak power density of 177 mW·cm−2 and competitive durability (200 h). Furthermore, the Al-air battery equipped with FeNC-NaCl-900 attained an ultrahigh specific capacity of 2257.48 mAh·g−1 at a large discharge current of 100 mA cm−2. These findings provide guidance for the development of high performance FeNC catalysts and their applications in metal-air batteries.

In-situ gas foaming synthesis of N, S-rich co-doped hierarchically ordered porous carbon as an efficient oxygen reduction reaction catalyst

The design and manufacture of cost-effective and efficient oxygen reduction reaction (ORR) catalysts is critical to the widespread application of multiple energy conversion devices. Herein, a combination of in-situ gas foaming and the hard template method is proposed to construct the N, S-rich co-doped hierarchically ordered porous carbon (NSHOPC) as an effective metal-free electrocatalyst for ORR via carbonizing a mixture of polyallyl thiourea (PATU) and thiourea in silica colloidal crystal template (SiO2-CCT) voids. Benefiting from the hierarchically ordered porous (HOP) architectures and the mass doping of N and S, NSHOPC displays excellent ORR activities (the half-wave potential of 0.889 V in 0.1 M KOH and 0.786 V in 0.5 M H2SO4) and long-term stability, which are all better than those of Pt/C. As the air cathode in a Zn-air battery (ZAB), NSHOPC exhibits a high peak power density of 174.6 mW·cm−2 and long-term discharge stability. The remarkable performance of the as-synthesized NSHOPC signifies broad prospects for actual applications in energy conversion devices.

Ag Anchored Atomically Around Nanopores of Porous Co(OH)2 for Efficient Bifunctional Oxygen Catalysis

AbstractVarious clean energy storage and conversion systems highly depend on rational design of efficient electrocatalysts for oxygen reactions. Increasing both gas molecular diffusion and intrinsic activity is critical to boosting its efficiency for bifunctional oxygen electrocatalysis. However, controllable synthesis of catalysts that combines gas molecular diffusion and intrinsic activity remains a fundamental challenge. Herein, a two‐step synthetic strategy is adopted to fabricate a composite oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalyst (P‐Ag‐Co(OH)2), of which, atomic Ag is anchored in reactive oxygen atoms around nanopores of Co(OH)2 nanosheets. Abundant nanopores provide enough gas molecular diffusion channels, and the special Ag‐O‐Co‐OH catalytic groups around nanopores display high intrinsic catalytic activity, which jointly result in an excellent ORR/OER performance. In alkaline electrolyte, P‐Ag‐Co(OH)2 displays a high half‐wave potential (0.902 V versus RHE) for ORR, and a low overpotential (235 mV at 10 mA cm−2) for OER, which is superior to non‐noble catalysts in previous studies and Pt/C (Ir/C) catalyst. At the same time, the single‐cell zinc‐air battery is prepared with an extremely high discharge peak power density of 435 mW cm−2 and excellent discharge–charge cycle stability.

High platinum utilization for proton exchange membrane fuel cells via low-temperature substrate sputtering on acid-treated carbon nanotube sheet

Low-temperature substrate sputtering on an acid-treated carbon nanotube (ATCNT) sheet result in high platinum (Pt) utilization. A thin catalyst layer (CL, ∼300 nm) with a high density of Pt and vacancies was formed on the ATCNT sheet (Pt-deposited ATCNT). It replaced the commercial carbon-supported Pt and microporous layers of the proton exchange membrane fuel cells. The substrate temperature (Tsub: 20, 5, −10, −30, and −50 ℃) contributed to crack formation in the porous Pt thin film and restrained the growth of Pt grain (average grain size from 8.60 to 3.97 nm). Below −10 ℃, the crack and grain size changed significantly. The increased crack and smaller grain size enlarged the Pt surface area while forming vacancies; this was confirmed via physical and electrochemical characterizations. When compared to Pt-deposited ATCNT (Tsub = 20 ℃, 47.61 m2 g-1Pt), the electrochemical surface area of Pt-deposited ATCNT (Tsub = -50 ℃, 72.06 m2 g-1Pt) increased by 51.35%. We present a high Pt mass-specific peak power density (5.93 kW g-1Pt), focusing on a strategy to increase Pt utilization.

N-doping FeNi@C(Nx) core-shell nanoparticles synthesized by arc plasma as a highly efficient bifunctional electrocatalyst for all-solid zinc-air batteries

Applications of zinc-air batteries (ZABs) are generally hampered by limited efficiency and poor stability of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode. The key to solving the problem is the highly efficient bifunctional electrocatalyst. Herein, the bifunctional electrocatalyst of nitrogen-doping carbon-coated FeNi (FeNi@C(Nx)) core-shell nanostructures was fabricated by one-step physical vapor evaporation technology of DC arc plasma and subsequent -nitrogen treatment. The energy state in the synthesis of FeNi@C precursor was monitored by a real-time optical emission spectroscopy (OES) measurement. The obtained FeNi@C(N15) nanoparticles was proved to be an excellent electrocatalyst for both ORR and OER processes, the OER overpotential is 326 mV which is better than that of RuO2 (405 mV) and the ORR catalytic reaction is close to the typical 4e− process. It is indicated that all-solid Zn-air battery assembled with this FeNi@C(N15) electrocatalyst provides a high open circuit voltage of 1.394 V, and a high peak power density of 59.7 mW cm−2. The synergistic effect between the bimetallic FeNi core and the N-doped carbon shell is responsible for the bifunctional activities, and such a core-shell nanostructure can prevent the catalyst from corrosion in working. This study provides a new approach for the design and preparation of transition metal alloys nanostructures encapsulated into the carbon-shell with quantitative nitrogen-doping, such a core-shell structured nanocapsule has excellent potential as the electrochemical bifunctional catalyst in some renewable energy devices.