19 research outputs found
Carbon Nanofibers as Potential Catalyst Support for Fuel Cell Cathodes: A Review
No full textPolymer electrolyte membrane fuel cells (PEMFCs) are a fast growing next-generation energy conversion technology, which hold promising interest for transportation and other applications. Nevertheless, successful commercialization of PEMFCs has been significantly retarded principally due to the high cost and poor durability of Pt/C catalysts used for anodic and cathodic reactions. Under typical fuel cell operating conditions, a traditional Pt/C catalyst is prone to degrade by various mechanisms, such as electrochemical carbon corrosion, which results in detrimental effects on the long-term performance. There have been tremendous efforts undertaken to develop durable carbon supports by introducing graphitic carbon components. In this context, carbon nanofiber supported catalysts have been investigated as highly durable supports for Pt and non-Pt nanoparticles in recent years. We anticipate it is timely to review the developments in this topic. This Review highlights the current progress on the graphitic nanofibers as a catalyst support in terms of morphology, electrocatalytic activity, various functionalization strategies, and so on, specifically focusing on the effect of nanofiber edge carbons and the advantages of surface reconstruction of nanofiber edge carbon into loops with regard to the stability of carbon support and fuel cell performance. We believe this Review stands as a guide for future researchers to figure out a rational design of oxygen reduction reaction catalysts, especially dealing with highly graphitized carbons.
M-N4 makrotsüklilised katalüsaatorid hapniku redutseerumis- ja eraldumisreaktsiooni elektrokatalüüsis
No full textVäitekirja elektrooniline versioon ei sisalda publikatsiooneBifunktsionaalsed katalüsaatormaterjalid on vajalikud koostisosad mitmesugustes elektrokeemilistes seadmetes, kus nad elektrokatalüüsivad hapniku redutseerimisreaktsiooni ja hapniku eraldumisreaktsiooni. Need reaktsioonid toimuvad mitmetes elektrokeemilistes energia muundamise ja salvestamise tehnoloogiates, näiteks kütuseelementides, metall-õhk akudes ja elektrolüüserites, mis võimaldavad üleminekut fossiilkütustel põhinevatelt energiasüsteemidelt. Doktoritöö eesmärk oli uurida siirdemetallidel põhinevate materjalide bifunktsionaalseid elektrokatalüütilisi omadusi hapniku redutseerimis- ja eraldumis-reaktsioonil. Katalüsaatormaterjalidena kasutati bimetalseid ftalotsüaniinidega dopeeritud süsiniknanotorusid ja teisi süsiniknanomaterjale ning ka polümeersetel võrgustikel põhinevaid siirdemetallidega dopeeritud materjale. Uuringute põhiline fookus oli hapniku redutseerimis- ja eraldumisreaktsiooni elektrokatalüütilist aktiivsust määravate tegurite väljaselgitamine, et leida materjalide struktuuri ja omaduste vahelisi seoseid ning arendada veelgi paremaid katalüsaatoreid. Neid materjale kasutati katoodkatalüsaatorina anioonvahetusmembraaniga kütuseelementides ja õhuelektroodina tsink-õhk akudes, kus need näitasid suurepärast jõudlust ja mõnedki neist ületasid kommertsiaalsete väärismetallkatalüsaatoritega saadud jõudluse. Doktoritöö raames tehtud laiahaardelised uuringud ulatusid uudsete katalüsaatormaterjalide sünteesist kuni nende elektrokeemiliste omaduste süvaanalüüsini, andes seega olulise panuse elektrokatalüüsi valdkonnale.Bifunctional oxygen electrocatalysts have emerged as pivotal components in a broad spectrum of electrochemical devices, playing a crucial role in facilitating the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). These reactions are crucial in various electrochemical energy conversion and storage technologies, including fuel cells, metal-air batteries and water electrolysers, thereby aiding in the transition away from reliance on fossil fuel-based energy systems. The aim of this doctoral thesis was to explore the electrocatalytic performance of a range of first-row transition metal-based materials for bifunctional oxygen electrocatalysis. These materials encompassed bimetal-doped carbon nanotubes, catalysts doped with metal phthalocyanines on various commercial carbon supports and polymer framework-derived carbon materials doped with transition metals. The specific focus of this investigation was to elucidate the influence of various factors on the ORR and OER activity. The key objective was to develop better electrocatalysts and to establish relationships between their structure and properties. These materials were employed as cathode catalysts in anion-exchange membrane fuel cells and as air electrodes in zinc-air batteries, demonstrating exceptional performance with several of them matching or even surpassing the performance of commercial noble metal-based catalysts. This comprehensive research spanning from the synthesis of novel catalyst materials to the thorough analysis of their electrochemical behaviour, strives to make a meaningful contribution to the dynamic field of electrocatalysis.https://www.ester.ee/record=b564545
Structurally Modulated Graphitic Carbon Nanofiber and Heteroatom (N,F) Engineering toward Metal-Free ORR Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells
No full textThe present study
designates the heteroatom (N,F)-doped various
graphitic carbon nanofibers (GNFs) viz. GNF-linear segmented platelets,
antlers, herringbone type, and their structural deformations from
pristine fiber with many open-edge active centers as metal-free, cost-effective
electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte
membrane fuel cells (PEMFCs). Introduction of heteroatoms to GNF frameworks
enlarges the lattice spacing between graphene platelets and leads
to structural modulation. The developed GNF/N–F catalysts show
excellent ORR activity with insensitivity to CH3OH and
demonstrated outstanding electrochemical potential cycling stability
of 10,000 cycles with well-retained ORR kinetics without much loss
in the activity. X-ray photoelectron spectroscopy investigation of
GNF/N–F catalysts explicitly shows the highly active forms
of N (pyridinic, pyrrolic, and graphitic-N) and semi-ionic, ionic
C–F of F in the catalysts. The deep-rooted synergistic effect
among N and F atoms creates more active centers entrenched with extensive
C–C bond polarization and larger charge delocalization with
larger spin density differences accomplished in GNF/N–F catalysts.
Wide open-edge cavities, opened tips, and many extensively accessible
facets collectively enhance the ORR activity of the GNF-H/N–F
catalyst. The present study provides a deep insight into the understanding
of advanced metal-free electrocatalysts for efficient ORR in PEMFCs
and metal–air batteries
Surfactant templated nanoporous carbon-Nafion hybrid membranes for direct methanol fuel cells with reduced methanol crossover
No full textN, F, and Fe-Doped Mesoporous Carbon Derived from Corncob Waste and Creating Oxygen Reduction Reaction Active Centers with a Maximum Charge Density of 0.25 for a Polymer Electrolyte Fuel Cell Catalyst
No full textDefect
chemistry, increasing charge, and spin density in the carbon
lattice are keys to the advancement of any alternative non-precious
cathodic oxygen reduction electrocatalyst for broad dissemination
of polymer electrolyte fuel cells (PEFCs). In view of this prospective,
we developed porous carbon from a biomass-derived source, such as
corncob (CC) waste, and heteroatom N and F doping on it to increase
functionalities and defects. Fe was further incorporated in N–F/CC-C
to enhance the oxygen reduction reaction (ORR) activity and power
density in PEFCs. Finely mesoporous carbon derived from CC undergoes
structural transformation, having numerous open edge active sites
after N–F co-doping, and alters the textural characteristics
favorable for ORR. The Fe/N–F/CC-C catalyst shows outstanding
ORR activity, insensitivity toward CH3OH in alkaline conditions,
and insignificant deprivation in ORR activity after a recurrent 10 000
potential cycles that prevails a highly enticing ORR electrocatalyst
for PEFCs. The presence of active pyridinic, pyrrolic, and graphitic
kinds of nitrogen along with ionic and semi-ionic active bonds between
C and F in graphitic arrangement of the Fe/N–F/CC-C catalyst
cumulatively ameliorates the catalytic activity. Furthermore, generation
of maximal C–C bond polarization, redistribution in charge
density, and high spin densities in the carbon lattice of the catalysts
were theoretically investigated, which cumulatively boost the ORR
activity
Heteroatom Engineering and Co-Doping of N and P to Porous Carbon Derived from Spent Coffee Grounds as an Efficient Electrocatalyst for Oxygen Reduction Reactions in Alkaline Medium
No full textProton Conducting Nafion-Sulfonated Graphene Hybrid Membranes for Direct Methanol Fuel Cells with Reduced Methanol Crossover
No full textNitrogen–Fluorine Dual Doped Porous Carbon Derived from Silk Cotton as Efficient Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells
No full textPorous carbon derived from silk cotton
and heteroatom engineering is explored in this study for developing
metal-free electrocatalysts for oxygen reduction (ORR). Individual
and dual doping of N and F heteroatoms was conducted to regulate defects
and the pore geometry to the porous carbon matrix. Microscopic analysis
of N–F co-doped cotton carbon (N–F/CTC) undergoes morphological
amendments in its textural properties and defects responsible in creating
active sites for ORR. N–F/CTC catalyst exhibits excellent ORR
catalytic activity and methanol and CO tolerance in the alkaline medium,
which makes it a potential metal-free ORR catalyst for the polymer
electrolyte membrane fuel cell. N–F/CTC catalyst is subjected
to 10 000 repeated potential cycles with no degradation in
its activity. XPS analysis of N–F/CTC catalyst revealed the
presence of N in the form of pyridinic-N, pyrrolic-N, graphitic-N,
active species, and F in the form of C–F ionic and C–F
semi-ionic active forms. The maximum C–C bond polarization,
charge redistribution, and high spin densities in the carbon matrices
are attained by all these active forms present in the catalyst and
synergistically enhance the ORR activity
Simultaneous Co-Doping of Nitrogen and Fluorine into MWCNTs: An In-Situ Conversion to Graphene Like Sheets and Its Electro-Catalytic Activity toward Oxygen Reduction Reaction
No full textSimultaneous Co-Doping of Nitrogen and Fluorine into MWCNTs: An In-Situ Conversion to Graphene Like Sheets and Its Electro-Catalytic Activity toward Oxygen Reduction Reaction
No full textIn the process of developing non-metallic electro-catalyst for oxygen reduction reaction (ORR), simultaneous co-doping of N and F into Multiwalled carbon nanotubes (MWCNTs) are synthesized and their structural and electrochemical properties are investigated. Microscopic analysis confirms that N-F/MWCNTs undergo structural transformation to wrinkled graphene like structures with many open-edge active sites favorable for ORR. The enhanced catalytic activity with dominant 4 electron transfer process during ORR is evidenced for the N-F/MWCNT catalysts. N-F/MWCNT catalyst has no effect on CH3OH or CO, which makes it highly desirable as metal-free ORR catalyst for polymer electrolyte fuel cell (PEFC) applications. The developed catalyst is subjected to 10,000 repeated potential cycles in acidic media and found absolutely no degradation in their ORR activity. XPS analysis of N-F/MWCNT exhibited the presence of active graphitic-N, pyridinic-N species and active semi-ionic C-F bonds. The co-existence of all these species induces the maximum polarization of C-C bonds in the graphitic matrix and synergistically enhances the ORR
