A systematic study of the preparation of porphyrins with extended conjugation by meso,β-fusion with polycyclic aromatic hydrocarbons (PAHs) is reported. The meso-positions of 5,15-unsubstituted porphyrins were readily functionalized with PAHs. Ring fusion using standard Scholl reaction conditions (FeCl(3), dichloromethane) occurs for perylene-substituted porphyrins to give a porphyrin β,meso annulated with perylene rings (0.7:1 ratio of syn and anti isomers). The naphthalene, pyrene, and coronene derivatives do not react under Scholl conditions but are fused using thermal cyclodehydrogenation at high temperatures, giving mixtures of syn and anti isomers of the meso,β-fused porphyrins. For pyrenyl-substituted porphyrins, a thermal method gives synthetically acceptable yields (>30%). Absorption spectra of the fused porphyrins undergo a progressive bathochromic shift in a series of naphthyl (λ(max) = 730 nm), coronenyl (λ(max) = 780 nm), pyrenyl (λ(max) = 815 nm), and perylenyl (λ(max) = 900 nm) annulated porphyrins. Despite being conjugated with unsubstituted fused PAHs, the β,meso-fused porphyrins are more soluble and processable than the parent nonfused precursors. Pyrenyl-fused porphyrins exhibit strong fluorescence in the near-infrared (NIR) spectral region, with a progressive improvement in luminescent efficiency (up to 13% with λ(max) = 829 nm) with increasing degree of fusion. Fused pyrenyl-porphyrins have been used as broadband absorption donor materials in photovoltaic cells, leading to devices that show comparatively high photovoltaic efficiencies.

A systematic study of the interaction between π-extended porphyrins and single-walled carbon nanotubes (SWNTs) is reported here. Zinc porphyrins with 1-pyrenyl groups in the 5,15-meso positions, 1, as well as compounds where one or both of the pyrene groups have been fused at the meso and β positions of the porphyrin core, 2 and 3, respectively, have been examined. The strongest binding to SWNTs is observed for porphyrin 3, leading to debundling of the nanotubes and formation of stable suspensions of 3-SWNT hybrids in a range of common organic solvents. Absorption spectra of 3-SWNT suspensions are broad and continuous (λ=400-1400 nm), and the Q-band of 3 displays a significant bathochromic shift of 33 nm. The surface coverage of the SWNTs in the nanohybrids was estimated by spectroscopic and analytical methods and found to reach 64% for (7,6) nanotubes. The size and shape of π-conjugated porphyrins were found to be important factors in determining the strength of the π-π interactions, as the linear anti-3 isomer displays more than 90% binding selectivity compared to the bent syn-3 isomer. Steady-state photoluminescence measurements show quenching of porphyrin emission from the nanohybrids. Femtosecond transient absorption spectroscopy reveals that this quenching results from ultrafast electron transfer from the photoexcited porphyrin to the SWNT (1/kCT=260 fs) followed by rapid charge recombination on a picosecond time scale. Overall, our data demonstrate that direct π-π interaction between fused porphyrins and SWNTs leads to electronically coupled stable nanohybrids.

With the growth of new energy economy, proton exchange membrane fuel cell (PEMFC) has great potential to be success. However, the lack of high-performance catalyst layer (CL) especially at cathode limits its applications. It is becoming increasingly important to understand interface property during electrocatalytic oxygen reduction reaction (ORR). Here, the rotating disk electrode (RDE) method is developed to study the temperature and Nafion ionomer content effects on interface formed between Nafion and Pt/C. The results show that the temperature has the significant influence on electrochemical active sites, charging double capacitance, and reaction polarization resistance at low Nafion content region. Excess Nafion loaded in CLs will turn to self-reunion and increase the exposed active sites. We find that the optimum Nafion loading is in the range of 30 to 40 wt.%. The highest specific activity we achieve is 107.8 μA/cm 2 .Pt at 60°C with 0.4 of ionomer/catalyst weight ratio, corresponding to the kinetic current 283.5 μA at 0.9 V. This finding provides new insights into enhancing the Pt utilization and designing high-efficiency catalysts for ORR.

Summary Gas diffusion layer (GDL) plays an important role in the performance of membrane electrode assembly (MEA) in polymer electrolyte fuel cells. In this work, 2‐type MEAs were prepared by 2 different GDLs of 29 BC and 29‐WUT, and the performance were investigated using polarization curve methods. The performance of MEA with 29‐WUT was 120 mV higher than 29 BC at 1600 mA/cm2. Electrochemical impedance spectroscopy (EIS) was applied to measure the mass transport resistance of 2‐type MEAs under normal running condition. The results of EIS showed that the mass transport resistance of 29 BC was 3.15 times higher than that of 29‐WUT at 1600 mA/cm2. To clarify this phenomenon, limiting current methods were applied under diluting oxygen concentration, low humidity, and high flow rate conditions. The results of limiting current methods showed that both the total oxygen transport resistance and the molecular diffusion resistance in the GDL of 29 BC were larger than that of 29‐WUT due to the lower porosity of gas diffusion substrate in 29 BC. As a result, EIS can be well combined with limiting current methods to analyze oxygen transport resistance in GDLs of fuel cells.

No abstract

Well-defined triblock copolymers with a photocleavable middle block were synthesized by RAFT polymerization and the photodegradation process was tracked by GPEC.

No abstract

In this paper, we evaluated the oxygen reduction reaction (ORR) activities of Pt/C, PtCo/C, and PtCoMn/C catalysts using charge-transfer resistance (Rct) and ΔRct onset voltage from electrochemical impedance spectroscopy as indicators in proton exchange membrane fuel cells (PEMFC) over a wide voltage range of 0.66 V∼0.95 V. ORR activity of the PtCoMn/C ternary alloy catalyst is higher than that of Pt/C over a large voltage range. A decal transfer method was used to prepare a membrane electrode assembly (MEA) with PtCoMn/C as a cathode catalyst. The cross-sectional micrograph of MEA-PtCoMn/C was characterized using scanning electron microscopy. A continuous ultrathin cathode catalyst layer that was 3 μm thick was successfully prepared. The performance of MEA-PtCoMn/C with an ultralow Pt loading of 0.147 mg/cm2 was evaluated using the single cell test. The highest achieved power density of MEA-PtCoMn/C was 1.42 W/cm2. The corresponding amount of platinum was 0.1035 gPt/kW, which reaches the index of the Department of Energy (DOE).