ABSTRACT
Lowering platinum (Pt) loadings without sacrificing power density and durability in fuel cells is highly desired yet challenging because of the high mass transport resistance near the catalyst surfaces. We tailored the three-phase microenvironment by optimizing the ionomer by incorporating ionic covalent organic framework (COF) nanosheets into Nafion. The mesoporous apertures of 2.8 to 4.1 nanometers and appendant sulfonate groups enabled the proton transfer and promoted oxygen permeation. The mass activity of Pt and the peak power density of the fuel cell with Pt/Vulcan (0.07 mg of Pt per square centimeter in the cathode) both reached 1.6 times those values without the COF. This strategy was applied to catalyst layers with various Pt loadings and different commercial catalysts.
ABSTRACT
Dual ion batteries (DIBs) have recently attracted ever-increasing attention owing to the potential advantages of low material cost and good environmental friendliness. However, the potential safety hazards, cost, and environmental concerns mainly resulted from the commonly used nonaqueous organic solvents severely hinder the practical application of DIBs. Herein, a hybrid aqueous/nonaqueous water-in-bisalt electrolyte with both broad electrochemical stability window and excellent safety performance is developed. The lithium-based DIB assembled using KS6 graphite and niobium pentoxide as the active materials in the cathode and anode exhibits good comprehensive performance including capacity, cycling stability, rate performance, and medium discharge voltage. Initial capacities of ≈47.6 and 29.6 mAh g-1 retention after 300 cycles can be delivered with a medium discharge voltage of around 2.2 V in the voltage window of 0-3.2 V at the current density of 200 mA g-1 . Good rate performance for the battery can be indicated by 29.7 mAh g-1 discharge capacity retention at 400 mA g-1 . It is noteworthy that the coulombic efficiency of the battery can reach as high as 93.9%, which is comparable to that of the corresponding DIBs using nonaqueous organic electrolytes.
ABSTRACT
Sodium nitrate is a main component of aging sea salt aerosol, and its phase behavior has been studied repeatedly with wide ranges observed in the efflorescence relative humidity (RH) in particular. Studies of the efflorescence dynamics of NaNO3 droplets deposited on a ZnSe substrate are reported, using an in situ Fourier transform infrared attenuated total reflection (FTIR-ATR) technique. The time-dependence of the infrared spectra of NaNO3 aerosols accompanying step changes in RH have been measured with high signal-to-noise ratio. From the IR difference spectra recorded, changes of the time-dependent absorption peak area of the O-H stretching band (ν-OH, â¼3400 cm(-1)) and the nitrate out-of-plane bending band (ν2-NO3(-), â¼836 cm(-1)) are obtained. From these measurements, changes in the IR signatures can be attributed to crystalline and solution phase nitrate ions, allowing the volume fraction of the solution droplets that have crystallized to be determined. Then, using these clear signatures of the volume fraction of droplets that have yet to crystallize, the homogeneous and heterogeneous nucleation kinetics can be studied from conventional measurements using a steady decline in RH. The nucleation rate measurements confirm that the rate of crystallization in sodium nitrate droplets is considerably less than in ammonium sulfate droplets at any particular degree of solute supersaturation, explaining the wide range of efflorescence RHs observed for sodium nitrate in previous studies. We demonstrate that studying nucleation kinetics using the FTIR-ATR approach has many advantages over brightfield imaging studies on smaller numbers of larger droplets or measurements made on single levitated particles.
