Investigation of non-stoichiometric tungsten-oxides and carbides as the anode catalysts supports and additives for the proton exchange membrane fuel cells

Abstract

Gorivne ćelije sa protonski provodnom membranom (PEM) su elektrohemijski sistemi koji iz vodonika (goriva) i kiseonika/vazduha (oksidansa) proizvode ĉistu elektriĉnu energiju, toplotu i vodu. Masovnu proizvodnju i upotrebu gorivnih ćelija ograniĉava cena komponenti, pre svega cena katalizatora. Neĉistoća goriva (prisustvo CO) dovodi do razgradnje i trovanja katalizatora. Stoga, intenzivno se razvijaju jeftiniji i dugotrajniji katalizatori i njihovi interaktivni nosaĉi. U okviru ove doktorske disertacije razvijeni su nestehiometrijski oksidi i karbidi volframa kao nosaĉi/aditivi katalizatora baziranih na Pt i PtRu za PEM gorivne ćelije. Ispitivana je provodljivost, struktura, morfologija i sastav pripremljenih nosaĉa/aditiva i katalizatora. Katalizatori su ispitivani cikliĉnom voltametrijom i voltametrijom na rotirajućoj disk elektrodi. Graniĉne difuzione struje oksidacije vodonika (HOR) dostižu se vrlo brzo i zadržavaju konstantne vrednosti u širokoj oblasti potencijala koji odgovaraju anodnim potencijalima aktivne PEM gorivne ćelije. Posebna pažnja posvećena je ispitivanju tolerancije katalizatora na CO korišćenjem metode elektrooksidacije COads i kinetike HOR u prisustvu CO. Sintetisani katalizatori pokazuju veću katalitiĉku aktivnost i toleranciju na CO u odnosu na komercijalne katalizatore. Pripremljeni katalizatori korišćeni su kao anodni katalizatori u jediniĉnim PEM gorivnim ćelijama. Performanse su ispitivane pri razliĉitim radnim uslovima: H2/O2, H2+CO/vazduh, reformat/vazduh, na razliĉitim temperaturama. Najbolje performanse daje PEM gorivna ćelija sa anodnim katalizatorom 30% PtRu/WxCyOz koja na 70ºC ima ~40% veću iskorišćenost Pt u odnosu na komercijalni katalizator. Veća iskorišćenost implicira moguće smanjenje koliĉine Pt, a time i nižu cenu PEM gorivne ćelije.Proton exchange membrane (PEM) fuel cells are electrochemical systems that produce clean electricity, heat and water from hydrogen (fuel) and oxygen/air (oxidants). Mass production and use of fuel cells is limited by the price of components, primarily the price of catalysts. Fuel impurities (presence of CO) lead to decomposition and poisoning of the catalyst. That is why cheaper and longlasting catalysts and their interactive supports are being intensively developed. Within this doctoral dissertation, non-stoichiometric tungsten-oxides and carbides were developed as supports/additives for catalysts based on Pt and PtRu for PEM fuel cells. The conductivity, structure, morphology and composition of the prepared supports/additives and catalysts were investigated. The catalysts were tested by cyclic voltammetry and rotating disk electrode voltammetry. Limiting diffusion currents were reached very quickly and maintained constant values in a wide range of potentials that corresponding to the anode potentials of the active PEM fuel cell. Special attention was dedicated to the examination of the catalyst CO tolerance , using the method of electro-oxidation of COads and HOR kinetics in the presence of CO. The synthesized catalysts showed higher catalytic activity and CO tolerance compared to commercial catalysts. The prepared catalysts were used as anode catalysts in unit PEM fuel cells. Performance was tested under various operating conditions: H2/O2, H2+CO/air and reformate/air, at different temperatures. The best performance was achieved with a PEM fuel cell employing 30% PtRu/WxCyOz anode catalyst which had ~40% higher Pt utilization compared to a commercial catalyst at 70ºC. Higher utilization implies possible reduction of the Pt loading and thus a lower cost of the PEM fuel cell