Influence of the tungsten carbide and carbon anode catalyst supports on PEM fuel cell performance

Gorivne ćelije su elektrohemijski izvori struje koji direktno prevode hemijsku energiju goriva u električnu energiju. Vodonične gorivne ćelije (eng. Proton Exchange Membrane Fuel Cell, PEMFC) kao gorivo koriste vodonik, a kao oksidans kiseonik ili vazduh, a pored dobijene električne energije jedini prateći proizvodi su voda i toplota. Poslednjih godina se intenzivno razvijaju sistemi koji koriste PEMFC namenjeni snabdevanju električnom energijom pojedinačnih domaćinstava ili zgrada. Ovakvi sistemi (eng. Micro Combined Heat and Power, μCHP) koriste dobijenu toplotu, nastalu proizvodnjom električne energije, za grejanje/ hlađenje pojedinačnih domaćinstava ili zgrada. Kako centralnu komponentu μCHP sistema čine PEM gorivne ćelije, visoka cena komponenti PEMFC i opadanje performansi tokom dugotrajnog rada usporavaju široku primenu u decentralizaciji energetskih sistema. Oko 50% cene PEMFC čini cena korišćenog katalizatora, a promene u strukturi katalizatora nastale oksidacijom nosača katalizatora i niskom tolerancijom na nečistoće u gorivu direktno utiču na dugotrajnost upotrebe μCHP sistema za snabdevanje električnom energijom i toplotom. U okviru ove disertacije je razvijen i karakterisan interaktivan nosač katalizatora na bazi nanopraha volfram-karbida. Ovakav materijal služi kao nosač nekoliko različitih katalizatora (Pt, Pd, Pt-Pd i Pt-Ru). Pored ovoga pripremljen je i neplatinski katalizator na bazi kobalta. Rezultati fizičko-hemijske karakterizacije su korelisani sa elektrohemijskim merenjima, kako bi se dobio uvid u ponašanje sintetisanih katalizatora. Kinetika reakcije oksidacije vodonika je ispitana korišćenjem klasičnih metoda elektrohemije. Pokazano je da je reakcija oksidacije vodonika veoma brza na svim ispitivanim katalizatorima, tj. da je kinetički kontrolisana do nadnapona od 50 mV. Interakcija čestica Pt ili Pd sa nosačem od WC je opisana, i doprinos ove interakcije jasno ukazuje na mogućnost sniženja količine plemenitog metala na WC nosaču, što dovodi do sniženja cene katalizatora za PEMFC. Ispitivanje uticaja ugljen-monoksida na reakciju HOR je vršeno u smeši H2+ 2% CO, na svim pripremljenim katalizatorima, kao i komercijalnim Pt/C (40%) i Pt-Ru/C (50%)...Fuel cells are electrochemical power sources that directly transform chemical energy of fuels into electricity. Hydrogen fuel cells (Proton Exchange Membrane Fuel Cell, PEMFC) are fueled by hydrogen and oxygen as the oxidant, and in addition to the generated electric power only following products are water and heat. In recent years there are intensively developed systems using PEMFC dedicated for electricity supply individual households or buildings. Such systems (Micro Combined Heat and Power, μCHP) use the resulting heat from power generation for heating / cooling purposes of individual households or buildings. As the central component of the μCHP system is PEM fuel cell, high cost of PEMFC components and the decline in performance over the long term are slowing the wide application in the decentralized energy systems. About 50% of the PEMFC price arises from the catalyst used, and changes in the catalyst structure originated from oxidation of catalyst support and catalyst low tolerance to impurities in the fuel directly affect the lifetime of the μCHP system. This PhD thesis deals wuth the development and characterization of an interactive catalyst support based on tungsten carbide nanopowders. This material serves as a catalyst support for a number of different catalysts (Pt, Pd, Pt-Pd and Pt-Ru). In addition a non-nobel anode catalyst based on cobalt is prepared. The results of physico-chemical characterization are correlated with the electrochemical measurements, in order to gain insight into the behavior of synthesized catalysts. Kinetics of hydrogen oxidation was investigated using the traditional methods of electrochemistry. It is shown that the hydrogen oxidation reaction (HOR) is very fast at all tested catalysts, ie. that is kinetically controlled by the overvoltage of 50 mV. The interaction of Pt particles or Pd with WC catalyst support is described, and the contribution of this interaction clearly indicates the possibility of decreasing the amount of precious metal, which leads to catalyst price reduction for the PEMFC. Influence of the carbon monoxide on the HOR kinetics was investigated using a mixture H2 + 2% CO, at all prepared catalysts and commercial Pt/C (40%) and Pt-Ru/C (50%) catalysts. It is shown that..