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Abstract: In this work, a hierarchically porous and ultrathick “breathable” wood‐based cathode for high‐performance Li‐O2 batteries is developed. The 3D carbon matrix obtained from the carbonized and activated wood (denoted as CA‐wood) serves as a superconductive current collector and an ideal porous host for accommodating catalysts. The ruthenium (Ru) nanoparticles are uniformly anchored on the porous wall of the aligned microchannels (denoted as CA‐wood/Ru). The aligned open microchannels inside the carbon matrix contribute to unimpeded oxygen gas diffusion. Moreover, the hierarchical pores on the microchannel walls can be facilely impregnated by electrolyte, forming a continuous supply of electrolyte. As a result, numerous ideal triphase active sites are formed where electrolyte, oxygen, and catalyst accumulate on the porous walls of microchannels. Benefiting from the numerous well‐balanced triple‐phase active sites, the assembled Li‐O2 battery with the CA‐wood/Ru cathode (thickness: ≈700 µm) shows a high specific area capacity of 8.58 mA h cm−2 at 0.1 mA cm−2. Moreover, the areal capacity can be further increased to 56.0 mA h cm−2 by using an ultrathick CA‐wood/Ru cathode with a thickness of ≈3.4 mm. The facile ultrathick wood‐based cathodes can be applied to other cathodes to achieve a super high areal capacity without sacrificing the electrochemical performance. [ABSTRACT FROM AUTHOR]

The wettability, or hydrophobic-hydrophilic balance, of cathode catalyst layer influences the performance of the proton exchange membrane fuel cell. In this paper, cathode catalyst layer with different polytetrafluoroethylene contents are prepared, and the effect of hydrophobic-hydrophilic balance on the performance of the membrane electrode assembly is investigated intensively. It is found that wettability, or hydrophobic-hydrophilic balance, of cathode catalyst layer can significantly affect the performance of membrane electrode assembly, and it can be effectively tuned by varying the loading of polytetrafluoroethylene. With the addition of polytetrafluoroethylene, the hydrophobicity of cathode catalyst layer, reflected by the contact angel, can be changed from 135.6° of that without addition of polytetrafluoroethylene to 146.5° with 70 wt.% polytetrafluoroethylene addition, and the optimal addition amount is 50 wt.%. For our optimal membrane electrode assembly with optimal addition of polytetrafluoroethylene in cathode, its current density are recorded as 990 mA cm –2  at 0.7 V and 1400 mA cm –2  at 0.6 V, respectively; its maximum power density is up to 856 mW cm −2 . Furthermore, our polytetrafluoroethylene-incorporated membrane electrode assembly also exhibits excellent stability, and current density only drops from 1000 mA cm −2 to 900 mA cm −2 after a continuous operation of 60 h. [ABSTRACT FROM AUTHOR]

The performance of the proton exchange membrane fuel cell (PEMFC) is significantly improved through introducing nitrogen-doped carbon nanotubes (NCNTs) into the catalyst layer (CL) and microporous layer (MPL) of the membrane electrode assembly (MEA), it reveals by SEM images that the NCNTs are uniformly dispersed in CL and MPL, resulting in the more plenty of porosity, higher surface area, better conductivity, and better prevention of the layer cracks. The BET surface area and pore volume of MPL are increased by 88% and 77% respectively with the addition of 20 wt% of NCNTs in MPL. The membrane electrode assembly (MEA) with adding 20 wt% NCNTs both in cathode CL and in cathode GDL can yield the best cell performance. At a cell temperature of 70 °C and 30 psi back pressures, the current density is up to 1000 mA cm −2 at 0.7 V and 1600 mA cm −2 at 0.6 V, and the max power density reaches 997 mW cm −2 . [ABSTRACT FROM AUTHOR]

The Li–O 2 battery is one of the most promising next-generation energy storage systems due to its super-high theoretical energy density. However, its further development is impeded by the current cathode system, which exhibits low energy efficiency and poor cycling stability. Herein, we report a composite of vanadium nitride coated with nitrogen-doped carbon nanoribbons grown in situ on carbon paper (denoted as VN@C) as a novel binder-free cathode for Li–O 2 batteries. We find that the nitrogen-doped carbon coating can significantly improve the stability of VN and enhance the composite's ORR/OER activities. The Li–O 2 batteries with our optimal VN@C-850 cathodes achieve an initial discharge capacity of 8269 mA h g−1, a discharge-charge voltage gap of 0.88 V, and considerable cycling stability for 183 cycles with a cut-off capacity of 1000 mA h g−1, compared with 2027 mA h g−1, 1.21 V, and 12 cycles with uncoated VN cathodes. • In situ grown VN coated with N -doped carbon cathode was fabricated. • The cathode exhibited high capacity and excellent cyclability in Li–O 2 battery. • It is found that the synergetic effects between VN and N -doped carbon is existed. [ABSTRACT FROM AUTHOR]

Highly effective cathode materials are critical to improve existing Li–O 2 batteries. In this paper, we report a free-standing Co 3 O 4 @NiCo 2 O 4 sheet array cathode, which is prepared by in-situ growing an array of sword-like cobalt-based metal-organic framework (Co-MOF) sheets on a carbon cloth (CC) substrate, followed by impregnated with nickel nitrate solution and pyrolyzed in air flow. The Co 3 O 4 @NiCo 2 O 4 /CC cathode exhibits excellent ORR/OER bifunctional activity and high cathodic performance in a Li–O 2 battery, achieving a specific capacity of 10645 mAh g−1 and a stability of 225 cycles. We suggest the high performance of our cathode can be ascribed to its well-defined 3D sheet array structure, which can facilitate O 2 diffusion and electrolyte impregnation, provide sufficient space for the discharge products, and the synergistic effect between Co 3 O 4 and NiCo 2 O 4. This work provides an effective method for the rational design of electrode composition and structure. Image 1 • A sword-like Co 3 O 4 @NiCo 2 O 4 nanosheet array cathode for Li–O 2 battery is prepared. • The cathode exhibited enhanced bifunctional OER/ORR activities in Li–O 2 batteries. • The high performance can be ascribed to its hybrid and array structure. • A high specific capacity of 10645 mAh g−1 with stability of 225 cycles is achieved. [ABSTRACT FROM AUTHOR]

Core-shell structured catalysts, made by placing either a monolayer or a thin layer of a noble metal on relatively cheap core-metal nanoparticles, are fascinating and promising fuel cell catalysts due to their high utilization of noble metals. Here, we report our development of a core-shell structured catalyst, Ru@Pt/C, generated by a novel and facile pulse electrochemical deposition (PED) approach. We demonstrate that compared with a commercial Pt/C catalyst, this novel catalyst achieves over four times higher mass activity towards the anodic oxidation of methanol, and 3.6 times higher mass activity towards the cathodic reduction of oxygen. Importantly, we find that the intrinsic activity of Pt in this Ru@Pt/C catalyst is doubled due to the formation of the core-shell structure. The catalyst also shows superior stability: even after 2000 scans, it still retains up to 90% of the peak current. Our findings demonstrate that this novel PED approach is a promising method for preparing high-performance core-shell catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]