Electrochemical and physical characterization of pristine and activated molybdenum carbide - derived carbon electrodes for the oxygen electroreduction reaction
Date
2014-05-29
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Abstract
Polümeerelektrolüütmembraan-kütuseelement (PEMFC) on paljutõotavaks energiaallikaks portatiivsetes ja statsionaarsetes seadmetes. PEMFC on kõrge kasuteguri ja madala keskkonnareostusega ning töötab suhteliselt madalatel temperatuuridel. PEMFC efektiivsust enim piiravaks teguriks on hapniku redutseerumise reaktsiooni (ORR) aeglus katoodil. Seetõttu on paljud uurimustööd suunatud uute ORR katalüsaatorite arendamisele. ORR katoodse ülepinge vähendamiseks on erinevaid süsinikmaterjale aktiveeritud plaatina, plaatina-ruteeniumi ja teiste Pt-metallide sulamite ning d-metallide (Ni, Co, Fe, Cr) nanoklastritega.
Käesoleva töö eesmärgiks oli uurida Pt ja Pt Ru sulamist katalüsaatorite alusmaterjali omaduste mõju ORR kineetikale 0,5 M H2SO4 vesilahuses. Katalüsaatori nanoosakeste kandjana kasutati Mo2C pulbrist kuuel kloreerimistemperatuuril vahemikus 600 kuni 1000 °C sünteesitud mikro-mesopoorset süsinikmaterjali. Tulemusi võrreldi kommertsiaalsest süsinikkandjast Vulcan® XC72 valmistatud elektroodi andmetega.
Uuritud materjalide füüsikaliseks karakteriseerimiseks kasutati röntgenstruktuuranalüüsi, röntgenfotoelektronspektroskoopia, Raman spektroskoopia jt meetodeid. Materjalide morfoloogia ja süsiniku elektronkonfiguratsiooni määramiseks kasutati kõrglahutusega transmissioon-elektronmikroskoopiat (HRTEM) koos elektronide energiakao spektroskoopia ja valitud alalt elektronide difraktsiooni meetoditega. Pinna topograafia uurimiseks rakendati skaneerivat elektronmikroskoopiat. Materjali poorsus ja eripind määrati lämmastiku adsorptsiooni mõõtmistest ning tulemustest järeldus, et sünteesitemperatuur mõjutab oluliselt materjalide eripinda ning poorijaotust.
Elektrokeemiliseks karakteriseerimiseks kasutati tsüklilise voltamperomeetria, pöörleva ketaselektroodi ja elektrokeemilise impedantsi spektroskoopia meetodeid.
Alternative energy conversion systems are novel solution for the energy and environmental crisis due to the limited resources of fossil fuels and the globally increasing pollution level. Many countries have invested into development of the environmental friendly renewable-and hydrogen energy technology. Polymer electrolyte membrane fuel cell (PEMFC) is a promising alternative energy conversion system, which has very high electrical efficiency because the energy of the chemical reaction is directly converted into electrical energy. The overall efficiency can be increased even further if the generated heat is used as well. The electrochemical reactions occur on the surface of the catalyst, which usually is platinum nanoparticles supported onto the porous carbon. To minimize the use of platinum in the catalyst layer and through that the cost of a fuel cell, it is important to design a catalyst structure, which has small Pt-nanoparticles with large effective surface area finely dispersed at the porous surface of the catalyst support. This is the first systematic study where the molybdenum carbide derived carbons (C(Mo2C)) with tuneable porosity have been studied as a catalyst support for the oxygen electroreduction (ORR). For this work the C(Mo2C)s were prepared from Mo2C at six different fixed chlorination temperatures from 600 °C to 1000 °C and the ORR kinetics was studied on different pristine C(Mo2C) and Pt nanoclusters activated composite Pt-C(Mo2C) and Pt Ru alloy nanoclusters activated Pt-Ru-C(Mo2C) electrode materials in 0.5 M H2SO4 solution at 22 ± 1°C. It was demonstrated that ORR at micromesoporous carbons strongly depends on the C(Mo2C) synthesis temperature, i.e. on the porosity, pore size distribution, ratio of micropore and mesopore surface area and volume, crystallinity and amount of catalytically active defected areas, expressed at the C(Mo2C) surface.
Alternative energy conversion systems are novel solution for the energy and environmental crisis due to the limited resources of fossil fuels and the globally increasing pollution level. Many countries have invested into development of the environmental friendly renewable-and hydrogen energy technology. Polymer electrolyte membrane fuel cell (PEMFC) is a promising alternative energy conversion system, which has very high electrical efficiency because the energy of the chemical reaction is directly converted into electrical energy. The overall efficiency can be increased even further if the generated heat is used as well. The electrochemical reactions occur on the surface of the catalyst, which usually is platinum nanoparticles supported onto the porous carbon. To minimize the use of platinum in the catalyst layer and through that the cost of a fuel cell, it is important to design a catalyst structure, which has small Pt-nanoparticles with large effective surface area finely dispersed at the porous surface of the catalyst support. This is the first systematic study where the molybdenum carbide derived carbons (C(Mo2C)) with tuneable porosity have been studied as a catalyst support for the oxygen electroreduction (ORR). For this work the C(Mo2C)s were prepared from Mo2C at six different fixed chlorination temperatures from 600 °C to 1000 °C and the ORR kinetics was studied on different pristine C(Mo2C) and Pt nanoclusters activated composite Pt-C(Mo2C) and Pt Ru alloy nanoclusters activated Pt-Ru-C(Mo2C) electrode materials in 0.5 M H2SO4 solution at 22 ± 1°C. It was demonstrated that ORR at micromesoporous carbons strongly depends on the C(Mo2C) synthesis temperature, i.e. on the porosity, pore size distribution, ratio of micropore and mesopore surface area and volume, crystallinity and amount of catalytically active defected areas, expressed at the C(Mo2C) surface.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
süsinikelektroodid, elektrokeemiline reduktsioon, carbon-electrodes, electrochemical reduction