Graphitic carbon nitride-based photocatalysts: Toward efficient organic transformation for value-added chemicals production

Proton exchange membranes for high temperature proton exchange membrane fuel cells: Challenges and perspectives

Since severe global warming and related climate issues have been caused by the extensive utilization of fossil fuels, the vigorous development of renewable resources is needed, and transformation into stable chemical energy is required to overcome the detriment of their fluctuations as energy sources. As an environmentally friendly and efficient energy carrier, hydrogen can be employed in various industries and produced directly by renewable energy (called green hydrogen). Nevertheless, large-scale green hydrogen production by water electrolysis is prohibited by its uncompetitive cost caused by a high specific energy demand and electricity expenses, which can be overcome by enhancing the corresponding thermodynamics and kinetics at elevated working temperatures. In the present review, the effects of temperature variation are primarily introduced from the perspective of electrolysis cells. Following an increasing order of working temperature, multidimensional evaluations considering materials and structures, performance, degradation mechanisms and mitigation strategies as well as electrolysis in stacks and systems are presented based on elevated temperature alkaline electrolysis cells and polymer electrolyte membrane electrolysis cells (ET-AECs and ET-PEMECs), elevated temperature ionic conductors (ET-ICs), protonic ceramic electrolysis cells (PCECs) and solid oxide electrolysis cells (SOECs).

Water Electrolysis toward Elevated Temperature: Advances, Challenges and Frontiers.

The sheet-like material graphitic carbon-nitride (g-C3N4) is one of the most promising metal-free photocatalysts and utilized for various purposes, e.g. energy conversion, waste water remediation or organic synthesis. g-C3N4 features a suitable band gap in the visible light range and outstanding physicochemical stability. However, g-C3N4 features drawbacks such as structural disorder, low conductivity, poor dispersibility and in turn low processability. Amongst the strategies to improve g-C3N4 properties, combination with polymers is a promising avenue toward advanced materials. The present critical review highlights the development and investigation of g-C3N4/polymer combination, including (1) g-C3N4 as photoinitiator for polymer snythesis, (2) polymer modified g-C3N4 for improved dispersibility, (3) g-C3N4/polymer hybrid materials fabricated via physical or covalent attachment and (4) g-C3N4 based hydrogels. The fabrication methods and application of these areas will be critically reviewed and the advantage of g-C3N4/polymer combination comprehensively presented. Moreover, the broad range of applications is highlighted, e.g. photocatalysis, batteries, biosensors, H2 evolution and films. Finally, the review will conclude with a summary and perspective on future directions as well as current challenges of this research area in order to stimulate new research regarding the design and construction of g-C3N4/polymer materials.

/pdf/graphitic-carbon-nitride-and-polymers-a-mutual-combination-51ahlupx5n.pdf

Graphitic carbon nitride and polymers: a mutual combination for advanced properties

Poly(arylene piperidine)s with phosphoric acid doping as high temperature polymer electrolyte membrane for durable, high-performance fuel cells

A series of phosphoric acid (PA) doped imidazolium poly(phenylene oxide) (PPO) membranes with different methylimidazole (MeIM) contents were prepared to tailor the performance of solid-state membranes. First, brominated poly(phenylene oxide) (BPPO) was synthesized by methyl bromination. Then BPPO was reacted with MeIM and doped with PA. The process was confirmed by Fourier transform infrared spectroscopy and 13C NMR. The PA absorption ability of the imidazolium poly(phenylene oxide) (PPO-MeIM) membranes changed with increasing MeIM content. PPO-MeIM membrane showed the best proton conductivity of 6.79 × 10–2 S cm–1 at 0% relative humidity, the highest mechanical strength of 4.8 MPa at the molar ratio of 4:10 (M-3#) at 30 °C, and high power density of 260 mW cm–2 without additional humidification at 160 °C. Results indicated that incorporation of an appropriate amount of MeIM groups can achieve the best proton conduction performance and mechanical properties.

Effect of Methylimidazole Groups on the Performance of Poly(phenylene oxide) Based Membrane for High-Temperature Proton Exchange Membrane Fuel Cells

To achieve desirable performance of a polymer electrolyte membrane with higher proton conduction and better mechanical strength is a challenging work in the development of the phosphoric acid (PA) doped solid-state membrane for high temperature proton exchange membrane fuel cells. Firstly, phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (pPPO) was prepared by the bromination and phosphonation of poly(2,6-dimethyl-1,4-phenylene oxide). Afterward, a series of poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (PVP/pPPO) blend membranes and poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)–graphitic carbon nitride (PVP/pPPO/g-C3N4) nanocomposite membranes were prepared by a solution casting method. The PA uptake, volume swelling ratio, and proton conductivity of the PVP/pPPO blend membrane increased with increasing PVP content. But PA molecules drastically reduced the mechanical strength of the PVP/pPPO blend membrane. The incorporation of g-C3N4 improved the proton conduction and mechanical properties of the nanocomposite membrane due to the proton hopped sites provided by NH2 and the interaction of g-C3N4 and polymer chains. A higher proton conductivity of 74.4 mS cm−1 and a higher power density of 294 mW cm−2 at 180 °C without additional humidifying were observed for the PA doped PVP/pPPO nanocomposite membrane containing 5 wt% g-C3N4. The results show the PVP/pPPO nanocomposite membrane as a potential polymer electrolyte membrane for high temperature fuel cells.

Improved performance of poly(vinyl pyrrolidone)/phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)/graphitic carbon nitride nanocomposite membranes for high temperature proton exchange membrane fuel cells

To study the microscopic dispersion state of CO2 in different ester solvents, the solubility, volume expansion coefficients and in situ Fourier transform infrared (FTIR) spectra of the CO2–ester system were measured. The results show that the solubility and expansion coefficient of CO2 in ester solvents decreases as the hydrocarbon chain increases. As the pressure increases, the infrared absorption peaks of CO2 and the functional groups characteristic of ester molecules shift, indicating that CO2 molecules interact with ester molecules and that CO2 would destroy the interactions between the ester molecules. The hydrocarbon chain length of the ester molecules has a significant effect on the infrared absorption peak of the CO2–ester system. As the hydrocarbon chain length increases, the CO2 absorption peak shift and peak shift of the carbonyl groups in the ester gradually decrease.

/pdf/investigation-on-dispersion-properties-of-co2-and-ester-3pz3qy235p.pdf

Investigation on dispersion properties of CO2 and ester solvent mixtures using in situ FTIR spectroscopy

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Effect of Methylimidazole Groups on the Performance of Poly(phenylene oxide) Based Membrane for High-Temperature Proton Exchange Membrane Fuel Cells

Improved performance of poly(vinyl pyrrolidone)/phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)/graphitic carbon nitride nanocomposite membranes for high temperature proton exchange membrane fuel cells

Investigation on dispersion properties of CO2 and ester solvent mixtures using in situ FTIR spectroscopy