Search

Silica nanosheets (SN) derived from natural vermiculite (Verm) were successfully incorporated into polyethersulfone–polyvinylpyrrolidone (PES–PVP) polymer to fabricate high–temperature proton exchange membranes (HT–PEMs). The content of SN filler was varied (0.1–0.75 wt%) to study its influence on proton conductivity, power density and durability. Benefiting from the hydroxyl groups of SN that enable the formation of additional proton–transferring pathways, the inorganic–organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm2 at 150 °C without humidification when the content of SN is 0.25 wt%. Furthermore, exfoliated SN (E–SN) and sulfonated SN (S–SN), which were fabricated by a liquid–phase exfoliation method and silane condensation, respectively, were embedded in PES–PVP polymer matrix by a simple blending method. Due to the significant contribution from sulfonic groups in S–SN, the membrane with 0.25 wt% S–SN reached the highest proton conductivity of 51.5 mS/cm and peak power density of 546 mW/cm2 at 150 °C, 48% higher than the pristine PES–PVP membranes. Compared to unaltered PES–PVP membrane, SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150 °C. Using a facile method to prepare 2D SN from natural clay minerals, the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT–PEMs.

High–temperature proton exchange membrane fuel cells (HT–PEMFCs) are pursued worldwide as efficient energy conversion devices. Great efforts have been made in the area of designing and developing phosphoric acid (PA)–based proton exchange membrane (PEM) of HT–PEMFCs. This review focuses on recent advances in the limitations of acid–based PEM (acid leaching, oxidative degradation, and mechanical degradation) and the approaches mitigating the membrane degradation. Preparing multilayer or polymers with continuous network, adding hygroscopic inorganic materials, and introducing PA doping sites or covalent interactions with PA can effectively reduce acid leaching. Membrane oxidative degradation can be alleviated by synthesizing crosslinked or branched polymers, and introducing antioxidative groups or highly oxidative stable materials. Crosslinking to get a compact structure, blending with stable polymers and inorganic materials, preparing polymer with high molecular weight, and fabricating the polymer with PA doping sites away from backbones, are recommended to improve the membrane mechanical strength. Also, by comparing the running hours and decay rate, three current approaches, 1. crosslinking via thermally curing or polymeric crosslinker, 2. incorporating hygroscopic inorganic materials, 3. increasing membrane layers or introducing strong basic groups and electron–withdrawing groups, have been concluded to be promising approaches to improve the durability of HT–PEMFCs. The overall aim of this review is to explore the existing degradation challenges and opportunities to serve as a solid basis for the deployment in the fuel cell market.

Nowadays, oils and organics pollutions have become more serious, which causes great threats both to the ecological environment and human life. To solve this problem, development of absorbent materials with high absorption capacity and good recyclability for large-scale oils and organics separation from water still remains large challenge. In this work, we propose a facile and low-cost method to prepare 3-D PVDF/TPU composite foam with superoleophilicity (0°) and hydrophobicity (143°) by combining vacuum-assisted solution casting and particle leaching techniques. The proposed PVDF/TPU composite foam shows high absorption capacity toward different of oils and organics, and its maximum absorption capacity can achieve 55 g/g for dichloromethane, which is attributed to its high porosity (95%) and excellent interconnectivity. The absorbed oils and organics can be readily removed by simply squeezing the PVDF/TPU composite foam due to its outstanding elasticity, suggesting that it has prominent recyclability. More importantly, the composite foam can quickly and continuously separate oils and organics from water through a peristaltic pump and has a high separation efficiency of 98.5% even after 10 cycles, which indicating a promising prospect for cleaning the large-scale oils and organics pollutions. Furthermore, the composite foam also can be applied to separate surfactant-stabilized oils and organics in-water emulsion. These results showed that the PVDF/TPU composite foam has the potential to be widely applied in practice for oils and organics separation.

A machine-learning approach is used to segment 14 X-ray computed-tomography datasets acquired by lab-based scanning of laser-milled, high-temperature polymer electrolyte fuel cell samples mounted in a 3D-printed sample holder. Two modes of operation, one with constant current load and the other with current cycling, are explored and their impact on microstructural change is correlated with electrochemical performance degradation. Constant-current testing shows the overall quantity of phosphoric acid in the gas diffusion layers is effectively unchanged between 50 and 100 h of operation but that inter-electrode distribution becomes less uniform. Current-cycling tests reveal similar quantities of phosphoric acid but a different intra-electrode distribution. Membrane swelling appears more pronounced after current-cycling tests and in both cases, significant catalyst layer migration is observed. The present analysis provides a lab-based approach to monitoring microstructural degradation in high-temperature polymer electrolyte fuel cells and provides a more accessible and more statistically robust platform for assessing the impact of phosphoric acid mitigation strategies.

Oxysterol-binding protein–related protein (ORP) 4L acts as a scaffold protein assembling CD3-e, G-αq/11, and PLC-β3 into a complex at the plasma membrane that mediates inositol (1,4,5)-trisphosphat...

Nitrogen doping of the carbon is an important method to improve the performance and durability of catalysts for proton exchange membrane fuel cells by platinum-nitrogen and carbon-nitrogen bonds. This study shows that p-phenyl groups and graphitic N acting bridges linking platinum and the graphene/carbon black (the ratio graphene/carbon black=2/3) hybrid support materials achieved the average size of platinum nanoparticles with (4.88 +/- 1.79) nm. It improved the performance of the lower-temperature hydrogen fuel cell up to 0.934 W cm-2 at 0.60 V, which is 1.55 times greater than that of commercial Pt/C. Doping also enhanced the interaction between Pt and the support materials, and the resistance to corrosion, thus improving the durability of the low-temperature hydrogen fuel cell with a much lower decay of 10 mV at 0.80 A cm-2 after 30k cycles of an in-situ accelerated stress test of catalyst degradation than that of 92 mV in Pt/C, which achieves the target of Department of Energy (, 22 pages, 8 figures and supplementary information

To improve the performance and durability of phosphoric acid (PA) doped polybenzimidazole (PBI) membranes in high–temperature proton exchange membrane fuel cells (HT–PEMFCs), in this work, as–received natural muscovite (Mus), a clay material, was successfully incorporated into PBI matrix as an inorganic filler through the doctor blade method. The amount of Mus was varied (0.5–2 wt%) to explore its impact on the proton conductivity, mechanical and dimensional stability, power density, durability, and acid retention ability of the composite membranes. As the incorporation of Mus into membranes can introduce interactions with polymer chains and PA molecules to afford additional proton transport pathways at the interfaces in Mus–PBI and Mus–PA crosslinks, the membrane with 1 wt% Mus showed highest power density of 586 mW cm−2 at 150 °C without humidification, 24% higher than the pure PBI membrane (474 mW cm−2). Meanwhile, the PA doped composite membrane with 1 wt% Mus also displayed the highest mechanical strength (7.5 MPa) and lowest dimensional swelling (70.99% in area swelling and 202% in volume swelling). Compared with the pristine PBI membrane, the composite membranes had significantly improved durability under accelerated stress test (AST). The decreased ohmic resistance and increased polarization resistance after AST are related to the membrane thinning and the loss of catalyst active area, respectively. Most importantly, it was found that the strong interactions between Mus and PA molecules lead to improved acid retention ability of the composite membranes, thus less leached acid from the composite membrane reduces the negative effects on the catalyst degradation to alleviate degradation on cell performance and durability.

Reduced electrochemically exfoliated graphene oxide (rEGO) is combined with carbon black (CB) as a hybrid support material to improve platinum (Pt) catalyst electrochemical activity and durability. Pt/rEGO2-CB3 (rEGO/CB ratio 2/3) retains 71% of initial electrochemical surface area (ECSA) and maintains higher oxygen reduction reaction (ORR) activity compared to Pt/CB after 30000 cycles of the accelerated stress test (AST). In addition, Pt/rEGO2-CB3 shows a 1.8 times improvement in the hydrogen fuel cell performance compared with Pt/CB and is more stable after 24 h at a continuous 0.60 V. The Pt/rEGO2-CB3 promotes the 4e− reaction pathway demonstrated by linear sweep voltammetry (LSV), which leads to greater ORR activity. In addition, the combination of rEGO and CB leads to both enhanced transport properties and improved stability. The Pt particles on both CB and rEGO are less likely to agglomerate in the composite support than in either of the two carbon supports when used alone.

In this work, a 3D-printed reactor was designed to enable natural graphite flakes to be used for electrochemical exfoliation to quickly obtain graphene oxide. Graphite foil as a typical raw material of electrochemical exfoliation was also exfoliated for comparison. Under the same conditions (10 V, 1 mol L-1 ammonium sulphate solution as electrolyte), the graphene products obtained by one-step electrochemical exfoliation using natural graphite flakes based on the reactor, have a significantly higher degree of oxidation than products obtained using graphite foil (the oxygen content is increased by 50.2%). In addition, the degree of oxidation can be further increased by increasing the electrolyte concentration or reaction time. This design achieves one-step exfoliation using natural graphite flakes to obtain graphene oxide with tunable oxygen content in short time without using any strong oxidants or strong acids. The as-prepared electrochemically exfoliated graphene oxide (EGO) was used to prepare polybenzimidazole (PBI)/graphene oxide (GO) composite membranes for high-temperature polymer electrolyte membrane fuel cells (HTPEMFC). The 0.5%, 1% and 2% EGO loadings in the PBI membrane increased the peak power density by 13.8%, 24.4% and 29.2%, respectively.

Graphene, a two-dimensional (2D) structure of honeycomb lattice material with long-range π-conjugation, is an ideal catalyst support material due to its large surface area, excellent electrical conductivity, good mechanical and electrochemical stability [1]. It has already been reported that platinum nanoparticles (PtNPs) supported on reduced graphene oxide (rGO), is limited by van der Waals force resulting in the restacked rGO flakes during the reduction process, thereby hindering the transport of fuel gas to approach Pt active sites [2, 3]. To overcome this issue, several publications have successfully developed PtNPs catalyst supported on rGO and carbon black (CB) hybrid supporting materials [4]. The synergistic effect between rGO and CB could enhance its activity for oxygen reduction reaction through controlling PtNPs size as well as improve its durability by preventing the agglomeration and corrosion of supporting materials [3]. However, Hummers GO leads to environmental and safety issues (use KMnO4, strong oxidizing agents and concentrated H2SO4) as well as a long-time preparation with high cost [2]. Our previous research has already developed a novel graphene-based material prepared by electrochemical exfoliation of graphite, which is faster, more environmentally friendly and has a high yield, intercalated by CB as a bi-support and achieved 50% improvement performance compared with Pt/CB. To further improve catalyst activity, some research proposed that the introduction of nitrogen, especially graphitic N and pyridinic N, on the surface of carbon materials could improve ORR activity and electronic conductivity by changing the local electronic structure as well as polarization of the graphene network with smaller energy band gap [3, 5]. However, the effect and comparation of nitrogen doped rEGO intercalated by CB (NrEGO-CB) and nitrogen doped both EGO and CB (NrEGO-NCB) as bi-support materials to improve the performance of the hydrogen fuel cell have not been studied. In this work, EGO and EGO-CB was doped with nitrogen by hydrothermal treatment with urea as a nitrogen precursor in a Teflon-steel autoclave. Pt catalysts were synthesized by a modified polyol reduction method. Successful preliminary results can be observed in Fig 1, which shows that PtNPs supported on NrEGO-CB with ratio of 2 to 3 has a maximum power density of 1.2 W cm-2. It is more than 4 times compared with that 0.3 W cm-2 of Pt/CB. References [1] Haibo Wang, Thandavarayan Maiyalagan, Xin Wang. Review on recent progress in nitrogen-doped graphene: synthesis, characterization, and its potential applications. ACS Catalysis. 2012. 2 (5): 781-794. [2] Erwan Bertin, Adrian Münzer, Sven Reichenberger, Rene Streubel, Thomas Vinnay, Hartmut Wiggers, Christof Schulz, Stephan Barcikowski, Galina Marzun. Durability study of platinum nanoparticles supported on gas-phase synthesized graphene in oxygen reduction reaction conditions. Applied Surface Science. 2019. 467-468, 1181-1186. [3] W.H. Lee, H.N. Yang, K.W. Park, B.S. Choi, S.C. Yi, W.J. Kim. Synergistic effect of boron/nitrogen co-doping into graphene and intercalation of carbon black for Pt-BCN-Gr/CB hybrid catalyst on cell performance of polymer electrolyte membrane fuel cell. Energy. 2016. 96: 314-324. [4] Yujing Li, Yongjia Li, Enbo Zhu, Tait McLouth, Chin-Yi Chiu, Xiaoqing Huang, Yu Huang. Stabilization of high-Performance oxygen reduction reaction Pt electrocatalyst supported on reduced graphene oxide/carbon black composite. Journal of The American Chemical Society. 2012. 134: 12326-12329. [5] Yue Jiang, Jia Zhang, Yuanhang Qin, Dongfang Niu, Xinsheng Zhang, Li Niu, Xinggui Zhou, Tianhong Lu, Weikang Yuan. Ultrasonic synthesis of nitrogen-doped carbon nanofibers as platinum catalyst support for oxygen reduction. Journal of Power Source. 2011. 196: 9356-9360. Figure 1

Since its discovery in 2004, Graphene has been widely study for different applications, noticeable for electrochemical energy devices, due to its excellent properties as a barrier material, electrical conductivity or high surface area. However, it is still an expensive material since it cannot be produced in a large scale. Graphene based materials such as Graphene oxide (GO) or Reduced Graphene Oxide (rGO) also present similar properties than Graphene and can be produce in a more economical way [1]. However, traditional method to produce GO, Hummer’s method, which base on chemical exfoliation of graphite, is a long and tedious process which requires the use of strong oxidants and hazardous chemicals leading environmental pollution that cannot be repaired [2,3]. Recently, electrochemical exfoliation of graphite to produce GO has attracted more and more attention due its environmental protection, low price, easy process and high efficiency [4-7]. Since natural graphite is mostly in the form of flakes and its tiny size is not conducive to its direct use in electrochemical exfoliation, currently, electrochemical exfoliation is mostly made of graphite foil, graphite rod and other graphite processed products. These materials are obtained by using processes such as chemical, thermodynamic, and mechanical compression, leading in physical or chemical changes that alter their original properties or structure. There are also some attempts to use natural graphite flakes for electrochemical exfoliation [8,9]. However, this makes electrochemical exfoliation require more voltage, longer time and less yield. In this work, we present novel design reactor to perform electrochemical exfoliation using natural graphite flakes as raw materials. By using ammonium sulphate as electrolyte, electrochemical exfoliation of natural graphite flakes can be done at low voltage with short time. This achievement also enables the comparison of electrochemical exfoliation products with different raw materials (graphite foil and natural graphite flakes) at the same exfoliation voltage and the same exfoliation time. We explored the properties of the product by raman spectroscopy, ultraviolet–visible spectroscopy (UV-VIS), fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), four-probe method and contact angle measurement. We have found that by combining natural graphite flakes with the reactor, the product obtained is significantly different from the exfoliated product based on graphite foil, achieving better oxidation, better dispersion in deionized water, more defects and greater yield. In addition, the special structure of the reactor allows the exfoliation time to be controlled, and we also compare the products obtained at different exfoliation times. The Exfoliated Graphene Oxide (EGO) obtained it has been used as a filler material in proton exchange membranes for hydrogen fuel cells as well as a support material for electrocalyst to enhance the kinetics for the reactions which take place in these fuel cells. References: [1] Perreault F, De Faria A F, Elimelech M. Environmental applications of graphene-based nanomaterials[J]. Chemical Society Reviews, 2015, 44(16): 5861-5896. [2] Eigler S. Controlled Chemistry Approach to the Oxo‐Functionalization of Graphene[J]. Chemistry–A European Journal, 2016, 22(21): 7012-7027. [3] Eigler S, Hirsch A. Chemistry with graphene and graphene oxide—challenges for synthetic chemists[J]. Angewandte Chemie International Edition, 2014, 53(30): 7720-7738. [4] Gurzęda B, Florczak P, Kempiński M, et al. Synthesis of graphite oxide by electrochemical oxidation in aqueous perchloric acid[J]. Carbon, 2016, 100: 540-545. [5] Su C Y, Lu A Y, Xu Y, et al. High-quality thin graphene films from fast electrochemical exfoliation[J]. ACS nano, 2011, 5(3): 2332-2339. [6] Tian Z, Yu P, Lowe S E, et al. Facile electrochemical approach for the production of graphite oxide with tunable chemistry[J]. Carbon, 2017, 112: 185-191. [7] Liu J, Poh C K, Zhan D, et al. Improved synthesis of graphene flakes from the multiple electrochemical exfoliation of graphite rod[J]. Nano Energy, 2013, 2(3): 377-386. [8] Yu P, Tian Z, Lowe S E, et al. Mechanically-assisted electrochemical production of graphene oxide[J]. Chemistry of Materials, 2016, 28(22): 8429-8438. [9] Lowe S E, Shi G, Zhang Y, et al. Scalable Production of Graphene Oxide Using a 3D-Printed Packed-Bed Electrochemical Reactor with a Boron-Doped Diamond Electrode[J]. ACS Applied Nano Materials, 2019, 2(2): 867-878.

The electrolyte plays an important role in the Membrane Electrode Assembly (MEA) of Polymeric Electrolyte Membranes Fuel Cells, (PEMFCs), having three main functions, to act as ion conductor, electronic insulator and a separator for the reactant gases [1]. The electrolyte is a Proton Exchange Membrane and Nafion is the most widely used polymeric membrane in this technology. However, because its particular structure it requires a good hydration to lead a high proton conductivity, which limit the operating temperature to lower than 100 oC. Poly[2,2′-m-(phenylene)-5,5′-benzimidazole (PBI) membrane doped with Phosphoric Acid, has been presented as an alternative to Nafion membranes allowing higher operating temperatures, 200oC, which enhance the kinetics of the reactions. However, during the operation of High Temperature Fuel Cells (HT-PEMFCs) these membranes suffer Phosphoric Acid leaching leading to a low proton conductivity and degradation of the fuel cell [2]. The 2D honeycomb lattice of Graphene provides this material particular properties such as high surface area, exceptionally high electrical conductivity, good chemical and thermal stability and excellent barrier properties, which make it a potential material for a large number of applications. In addition to this [1], Hu. et al. [3] have demonstrated that Single Layer Graphene present a high proton conductivity being at the same time a barrier for other elements, which makes this material a potential electrolyte for PEMFC. However, SLG has some drawbacks notably due to the complex process to produce it and its high cost. These limitations leave an open window to Graphene based materials such as Graphene Oxide, which shows very attractive properties to act as filler in Nafion and PBI membranes due to its chemical functionalization and its non-porous structure, which provides additional resistance for mass transport and increases the tortuosity of the permeation pathways leading to higher selectivity [1]. Here we will describe the work carried out at University of Mancheschester incorporating SLG and GO composite membranes into the MEA of both PEM Fuel Cells, Low Temperature (LT-PEMFC) and HT-PEMFC. The addition of the SLG produced by CVD into the MEA of LT-PEMFC has demonstrated no change in the proton conductivity, supporting the hypothesis that SLG is a good proton conductor. In addition, for a particular LT-PEMFC, Direct Methanol Fuel Cells (DMFC), a decreasing of the methanol crossover has found leading a significant enhancement of the power density [4]. SLG has been also incorporated into the MEA of HT-PEMFC, which use PBI membrane instead of Nafion, to evaluate its proton conductivity and barrier properties, this time to stop the Phosphoric Acid leaching. Although positive results have been reported by adding SLG into the MEAs, a different approach has been conducted by the development of GO-composite membranes also for both type of PEMFC. Exfoliated Graphene Oxide has been synthesized by electrochemical exfoliation of graphite and has been incorporated as a filler into two different of matrix polymer, Nafion and PBI, to evaluate their performance in both PEMFC, high and low temperature. References: [1] Perez-Page Maria, Sahoo Madhumita, Holmes, M Stuart. Single Layer 2D Crystals for Electrochemical Applications of Ion Exchange Membranes and Hydrogen Evolution Catalyst. Advance Materials Interfaces (2019) 6, 1801838. [2] S. H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F. N. Buchi and T. J. Schmidt. Dynamic Operation of HT-OEFC: In-Operando Imaging of Phosphoric Acid Profiles and (Re)distribution. Journal of The Electrochemical Society, (2015), 162, 3, F310-F316. [3] S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu, A. K. Geim. Proton transport one-atom-thick crystals. Nature (2014), 516, 227. [4] Stuart M. Holmes, Orabhuraj Balakrishnan, Vasu. S. Kalangi, Xiang Zhang, Marcelo Lozada-Hidalgo, Pulickel M Ajayan, Rahul R. Nair. 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Advance Energy Materials, 7, (2017).