We recently showed that phase-pure molybdenum carbide nanotubes can be durable supports for platinum (Pt) nanoparticles in hydrogen evolution reaction (HER). In this paper we further characterize surface properties of the same Pt/β-MoC catalyst platform using carbon monoxide (CO)-Pt and CO-MoC bond strength of different Pt particle sizes in the <3 nm range. Results from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temporal analysis of products (TAP) revealed the existence of different active sites as Pt particle size increases. Correlation between the resultant catalyst activity and deposited Pt particle size was further investigated using water-gas-shift (WGS) as a probe reaction, suggesting that precise control of particle diameter and thickness is needed for optimized catalytic activity.
Ionic liquids (ILs) are environmentally friendly solvents that have been used to extract valuable compounds from coal and biomass. In this work, eight methylimidazolium-based ionic liquids were selected based on their different capabilities of interactions with solutes. ζ-Potential characterization was used as a descriptor to reveal the type of interactions (e.g., hydrogen bonding, π−π interaction, and dispersion force) between the chosen ILs and coal particles. Consequently, the different interactions with certain strengths between the selected cations/anions and coal particles provide unprecedented selectivity of ILs in coal extraction. For aromatic-rich bituminous coal, the ILs associated with Cl − preferably extracted polycyclic aromatic hydrocarbons (PAHs). In contrast, for the same cations, BF 4 − and SbF 6 − anions did not show significant PAH extraction for bituminous coal. On the other hand, for oxygen-rich subbituminous coal, the fatty acids (FAs) with more than 20 carbon atoms were found to be rich in the extracts from the ILs associated with Cl − , whereas the same C 4 mim + cation with BF 4 − , PF 6 − , and SbF 6 − anions extracted unique tricyclic diterpanes. As such, this study provides systematic experimental results demonstrating that ILs may be custom designed to extract targeted compounds from coal or other complex feedstock such as lignocellulosic biomass.
By incorporating a parallel wire collector in electrospinning process with a hot-drawing treatment, carbon fiber mats with well-aligned coal-derived carbon nanofibers (CCNFs) were successfully fabricated. It was previously reported that the well-aligned fiber orientation could facilitate the mass transfer of electrolyte ion. In this paper, we demonstrate that surface oxygen concentration, pore area/volume and electrical conductivity were also significantly enhanced by the well-aligned carbon fiber, compared the randomly aligned CCNFs. Consequently, the well-aligned CCNFs generated the areal specific capacitance of 1590 mF cm −2 at the current density of 4 mA cm −2 in 6M KOH solution, which outperformed the aligned carbon nanofibers derived from adding carbon nanotubes or graphene as fillers into polymer precursors. Finally, a carbon/carbon supercapacitor cell was assembled with the well-aligned CCNFs mats as electrodes, showing the areal energy density of 15 μWh cm −2 at the power density of 0.3 mW cm −2 , as well as gravimetric energy density of 30 Wh kg −1 at the power density of 0.6 kW kg −1 and the volumetric energy density of 18.2 mWh cm −3 at the scan rate of 50 mV s −1 . 88.6% specific capacitance of full cell was retained after 5000 cycles of charge-discharge running at current density of 1 A g −1 .
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