Proton Exchange Membrane Fuel Cells (PEMFCs): Advances and Challenges

The study of the electrochemical catalyst conversion of renewable electricity and carbon oxides into chemical fuels attracts a great deal of attention by different researchers. The main role of this process is in mitigating the worldwide energy crisis through a closed technological carbon cycle, where chemical fuels, such as hydrogen, are stored and reconverted to electricity via electrochemical reaction processes in fuel cells. The scientific community focuses its efforts on the development of high-performance polymeric membranes together with nanomaterials with high catalytic activity and stability in order to reduce the platinum group metal applied as a cathode to build stacks of proton exchange membrane fuel cells (PEMFCs) to work at low and moderate temperatures. The design of new conductive membranes and nanoparticles (NPs) whose morphology directly affects their catalytic properties is of utmost importance. Nanoparticle morphologies, like cubes, octahedrons, icosahedrons, bipyramids, plates, and polyhedrons, among others, are widely studied for catalysis applications. The recent progress around the high catalytic activity has focused on the stabilizing agents and their potential impact on nanomaterial synthesis to induce changes in the morphology of NPs

Revisão sobre a síntese de grafeno por esfoliação em fase líquida: Mecanismos, fatores e técnicas

El objetivo del presente trabajo es crear un consenso acerca del método de exfoliación en fase líquida (LPE) para la producción de grafeno y, a su vez, conocer las causas y los diversos factores que afectan el rendimiento y la calidad del grafeno obtenido. Para lograr este objetivo, se realiza una revisión bibliográfica sistemática usando el buscador de Google Académico por la extensión de su acervo. En el presente escrito los resultados obtenidos de esta revisión bibliográfica exhaustiva de la LPE de grafeno se ordenan de acuerdo con su relevancia, dando prioridad en conocer las causas y los fenómenos físicos claves relacionados con la LPE. Los artículos centrados en entender los fenómenos físicos y químicos que gobiernan la LPE fueron clasificados en la sección mecanismo, con el fin de tener una mejor comprensión del fenómeno a nivel molecular. Con esta información, se propone una clasificación de acuerdo con las técnicas más comúnmente usadas (sonicación, microfluídica, etc) para lograr un consenso sobre las técnicas que se clasifican dentro del método de LPE de grafeno con base en el mecanismo, lo que da pauta al desarrollo de nuevas técnicas que mejoren significativamente el desempeño de este método. De la revisión sistemática se concluye que el método de exfoliación en fase líquida es un método robusto, atractivo para la industria, de fácil escalabilidad y de alto rendimiento en general dependiendo de las técnicas de preparación. The objective of this article is to create a consensus about the graphene production by the liquid-phase exfoliation (LPE) method, as well as to understand the key causes and factors affecting the yield and quality of the graphene obtained. An exhaustive bibliographic search was conducted in Google Scholar given the extent of its collection. The results of the search are ordered by relevance, giving priority to key causes and physical phenomena related to LPE. The articles focused on understanding physical and chemical phenomena were classified in the mechanism section, in order to have a better understanding of the method at the molecular level. With this information, a classification of the most common LPE techniques (sonication, microfluidics, etc.) is proposed in order to reach a consensus on which techniques belong to the LPE method in function of their mechanism. The proposed classification aims at developing new techniques to significantly improve the performance of this method. From this systematic review, it is concluded that the liquid-phase exfoliation method is robust and very attractive to the industry and has easy scalability with high performance in relation to the techniques analyzed.O objetivo do presente trabalho é criar um consenso no que diz respeito ao método de esfoliação em fase líquida (LPE) para a produção de grafeno e, por sua vez, conhecer as causas e os diversos fatores que afetam o desempenho e a qualidade do grafeno obtido. Para alcançar este objetivo, realiza-se uma revisão bibliográfica sistemática usando o buscador do Google Acadêmico na extensão de seu acervo. No presente escrito, os resultados obtidos desta revisão bibliográfica exaustiva da LPE de grafeno são ordenados segundo sua relevância, dando prioridade em conhecer as causas e os fenômenos físicos fundamentais relacionados com a LPE. Os artigos centralizados em entender os fenômenos físicos e químicos que governam a LPE foram classificados na seção mecanismo, objetivando ter uma melhor compreensão do fenômeno no âmbito molecular. Com essa informação, propõe-se uma classificação de acordo com as técnicas usadas com mais frequência (sonicação, microfluídica, etc.) para obter um consenso sobre as técnicas que são classificadas dentro do método de LPE de grafeno com base no mecanismo, o que dá pauta para o desenvolvimento de novas técnicas que melhorem significativamente o desempenho deste método. Da revisão sistemática, conclui-se que o método de esfoliação em fase líquida é um método robusto e atraente para a indústria, de fácil escalabilidade e de alto desempenho em geral, dependendo das técnicas de preparação

Nitrogen-carbon graphite-like semiconductor synthesized from uric acid

A new carbon-nitrogen organic semiconductor has been synthesized by pyrolysis of uric acid. This layered carbon-nitrogen material contains imidazole-, pyridine (naphthyridine)- and graphitic-like nitrogen, as evinced by infrared and X-ray photoelectron spectroscopies. Quantum chemistry calculations support that it would consist of a 2D polymeric material held together by hydrogen bonds. Layers are stacked with an interplanar distance between 3.30 and 3.36 Å, as in graphite and coke. Terahertz spectroscopy shows a behavior similar to that of amorphous carbons, such as coke, with non-interacting layers. This material features substantial differences from polymeric carbon nitride, with some characteristics closer to those of nitrogen-doped graphene, in spite of its higher nitrogen content. The direct optical band gap, dependent on the polycondensation temperature, ranges from 2.10 to 2.32 eV. Although in general the degree of crystallinity is low, in the material synthesized at 600 °C some spots with a certain degree of crystallinity can be found

Effect of Different Carbon Supports on the Activity of PtNi Bimetallic Catalysts toward the Oxygen Reduction

To evaluate supports’ effects on catalytic activity toward the oxygen reduction reaction (ORR), a simple and controlled chemical synthesis, involving the hot injection of metal precursors, was developed to produce bimetallic PtNi nanoparticles (75 wt.% Pt and 25 wt.% Ni), supported on carbon nanotubes (CNTs) and carbon nanofibers (CNFs). The synthesized electrocatalyst was characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning transmission electron microscopy (STEM). To determine the catalytic activity, an electrochemical evaluation of the synthesized catalysts in an acidic medium was performed using cyclic voltammetry (CV), CO stripping, and rotating disk electrode (RDE) tests. The presence of Pt and Ni in the nanoparticles was confirmed by EDS and XRD. Based on the STEM micrographs, the average particle size was 30 nm. Compared to the commercial Pt/C catalyst, the PtNi/CNT catalyst exhibited higher specific activity and slightly lower mass activity toward ORR in a 0.1 M HClO4 electrolyte solution

Nanoparticulated PdNi2 on mesoporous carbon: a methanol tolerant electrocatalyst for the oxygen reduction reaction

The kinetics of the oxygen reduction reaction (ORR) of PdNi 2 nanoparticles supported on a high specific area mesoporous carbon (MC) and Vulcan carbon was studied in the presence and absence of methanol in acid media. The electrocatalysts, synthesized by chemical reduction of the metal chlorides with NaBH 4 in aqueous media were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The catalyst supported on MC has a higher degree of Ni alloying and a smaller particle size than that supported on Vulcan. The electrochemical characterizations by RDE and DEMS indicate that PdNi 2 supported on the high surface area MC exhibits higher catalytic activity for the ORR, very similar to that of Pd- and Pt-based alloys with the advantage of a very low noble metal loading. Moreover, the PdNi 2 supported on MC shows an excellent methanol tolerance in acid media. Thus, this novel combination catalyst/support would be a suitable cathodic catalyst for direct methanol fuel cells.Fil: Ramos Sánchez, Guadalupe. CENTRO DE INVESTIGACIÓN Y DE ESTUDIOS AVANZADOS ; INSTITUTO POLITÉCNICO NACIONAL;Fil: Bruno, Mariano M.. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: Thomas, Yohann. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Corti, Horacio Roberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Solorza Feria, Omar. CENTRO DE INVESTIGACIÓN Y DE ESTUDIOS AVANZADOS ; INSTITUTO POLITÉCNICO NACIONAL

Synthesis and characterization of organic agar-based membranes for microbial fuel cells

[EN] The goal of this work was the synthesis and characterization of agar membranes for microbial fuel cells applications. Three sets of membranes were synthesized. For a first set of membranes (2, 4, 6, and 8 wt% agar concentration), both proton conductivity (sigma) and O-2 permeability (OP) increased as a function of agar concentration, up to 4 wt% agar. Beyond this concentration, the a levelled-off at 2.43 mS cm(-1) and OP increased. A second one set was obtaining by mixing 2, 4, 6, and 8 wt% concentrations of agar with KC110 wt%. Both a and OP increased as a function of increased agar concentration; nevertheless, the presence of KCl slightly affected in a negative way the OP. For the last set, agar concentration was fixed at 2 wt%, while KCl concentration was increased to 2, 4, 6, 8, and 10 wt%. The a did not significantly increase with salt concentration and the worst values of OP were observed. It was thus confirmed that agar concentration plays a significant role in the increase of a, but KCl does not improve membrane performance. Moreover, the agar membranes cost is two orders of magnitude lower than Nafion (R) 117. Therefore, the best membranes were those produced solely with agar.The authors gratefully acknowledge the support provided by CONACYT, Mexico and Mr. Adrian Velazquez for the English revision of this work. Giovanni Hernandez Flores expresses his acknowledgements for his graduate scholarship. Partial financial support was provided by CINVESTAV-IPN and the Ministerio de Economia y Competitividad (MINECO), Spain, through project ENE/2015-69203-R.Hernández-Flores, G.; Andrio, A.; Compañ Moreno, V.; Solorza-Feria, O.; Poggi-Varaldo, HM. (2019). Synthesis and characterization of organic agar-based membranes for microbial fuel cells. Journal of Power Sources. 435:1-11. https://doi.org/10.1016/j.jpowsour.2019.226772S11143

Use of Novel Reinforced Cation Exchange Membranes for Microbial Fuel Cells

This work has been focused on the synthesis and characterization of different blended membranes SPEEK-35PVA (Water), SPEEK-35PVA (DMAc) prepared by casting and nanofiber-reinforced proton exchange membranes Nafion-PVA-15, Nafion-PVA-23 and SPEEK/PVA-PVB. The two first reinforced membranes were made up of Nafion (R) polymer deposited between polyvinyl alcohol (PVA) nanofibers. The last composite membrane is considered because the PVA is a hydrophilic polymer which forms homogeneous blends with SPEEK suitable to obtain high proton conductivity, while the hydrophobic PVB can produce blends in a phase separation morphology in which very low water uptake can be found. The synthesized membranes showed an outstanding stability, high proton conductivity, and enhanced mechanical and barrier properties. The membranes were characterized in single chamber microbial fuel cells (SCMFCs) using electrochemically enriched high sodic saline hybrid H-inocula (Geobacter metallireducen, Desulfurivibrio alkaliphilus, and Marinobacter adhaerens) as biocatalyst. The best performance was obtained with Nafion-PVA-15 membrane, which achieved a maximum power density of 1053 mW/m(3) at a cell voltage of 340 mV and displayed the lowest total internal resistance (Rint approximate to 522 Omega). This result is in agreement with the low oxygen permeability and the moderate conductivity found in this kind of membranes. These results are encouraging towards obtaining high concentrated sodic saline model wastewater exploiting MFCs.The authors wish to thank SEP and CINVESTAV-IPN for granting a PhD fellowship to one of the authors (KSK). We gratefully acknowledge the financial support of the National Council of Science and Technology, CONACYT, under grant FOINS 75/2012 and the Ministry of Science and Innovation of Spain through the project SP-ENE-20120718 and Support Programme for Research and Development of the Polytechnic University of Valencia through the project ref. 24761. Dr O. Solorza thanks Plan de Movilidad e Internalizacion Academica VLC/CAMPUS fellowship at the Universidad Politecnica de Valencia.Kamaraj, S.; Mollá Romano, S.; Compañ Moreno, V.; Poggi-Varaldo, HM.; Solorza-Feria, O. (2015). Use of Novel Reinforced Cation Exchange Membranes for Microbial Fuel Cells. Electrochimica Acta. 176:555-566. doi:10.1016/j.electacta.2015.07.042S55556617

Using Nano Zero-Valent Iron Supported on Diatomite to Remove Acid Blue Dye: Synthesis, Characterization, and Toxicology Test

This work aimed to synthesize and characterize nanoscale zero-valent iron (nZVI), supported on diatomaceous earth (DE) at two different molar concentrations, 3 and 4 M (nZVI-DE-1 nZVI-DE-2), to test the decolorization treatment of acid blue dye (AB) and perform a toxicological test using zebrafish. The synthesis of the nanoparticles was obtained using the chemical reduction method. The material was fully characterized by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy and specific surface area (BET). The results showed spherical forms in clusters between 20 and 40 nm of zero-valent iron supported on diatomaceous earth. The removal of 1 g/L of AB from water treated with nZVI-DE-1 and nZVI-DE-2 reached the decolorization of 90% and 98% of all dye. By contrast, controls such as nZVI and DE-1 and DE-2 removed 40%, 37%, and 24% of the dye. Toxicological analysis using zebrafish showed that AB causes a severe defect in development, and embryos die after exposure. However, the water samples treated with nZVI-DE-1 and nZVI-DE-2 are not harmful to the zebrafish embryos during the first 24 h. However, all embryos exposed to the new material for more than 48 hpf had cardiac edema, smaller eyes, and curved and smaller bodies with less pigmentation

Mesoporous carbon as Pt support for PEM fuel cell

A mesoporous carbon (MP) supported Pt nanocatalyst was evaluated as anode and cathode catalyst for PEM fuel cell. Kinetics study of the oxygen reduction reaction were characterized by using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques in acid media. Membrane electrode assemblies (MEAs) were prepared using Pt supported on MP as anodic and cathodic catalysts and the fuel cell performance evaluated. Polarization and power curves show a similar performance as cathode catalyst when compared to commercial catalyst while there is an 8% improvement when used as anode catalyst.Fil: Viva, Federico Andrés. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bruno, Mariano Martín. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: Franceschini, Esteban Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Thomas, Yohann. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ramos Sanchez, Guadalupe. Instituto Politécnico Nacional. Centro de Investigación y Estudios Avanzados. Departamento de Química; MéxicoFil: Solorza Feria, Omar. Instituto Politécnico Nacional. Centro de Investigación y Estudios Avanzados. Departamento de Química; MéxicoFil: Corti, Horacio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentin