Abstract
Altervalent hypo-d-oxides of transition metal series impose spontaneous dissociative adsorption of water molecules and pronounced membrane spillover transferring properties instantaneously resulting with corresponding bronze type (Pt/HxWO3) under cathodic, and/or its hydrated state (Pt/W(OH)6) responsible for the primary oxide (Pt-OH) effusion, under anodic polarization, this way establishing instantaneous reversibly revertible alterpolar bronze features (Pt/H0.35WO3 Pt/W(OH)6), and substantially advanced electrocatalytic properties of these composite interactive electrocatalysts. As the consequence, the new striking and unpredictable prospects both in law and medium temperature proton exchange membrane fuell cell (L&MT PEMFC) and water electrolysis (WE) have been opened by the interactive supported individual (Pt, Pd, Ni) or prevailing hyper-d-electronic nanostructured intermetallic phase clusters (WPt3, NbPt3, HfPd3, ZrNi3), grafted upon and within high altervalent capacity hypo-d-oxides (WO3, Nb2O5, Ta2O5, TiO2) and their proper mixed valence compounds, to create a novel type of alterpolar interchangeable composite electrocatalysts for hydrogen and oxygen electrode reactions. Whereas in aqueous media Pt (Pt/C) features either chemisorbed catalytic surface properties of H-adatoms (Pt-H), or surface oxide (Pt=O), missing any effusion of other interacting species, new generation and selection of composite and interactive strong metal-support interaction (SMSI) electrocatalysts in condensed wet state primarily characterizes interchangeable extremely fast reversible spillover of either H-adatoms, or the primary oxides (Pt-OH, Au-OH), or the invertible bronze type behavior of these significant interactive electrocatalytic ingredients. Such nanostructured type electrocatalysts, even of mixed hypo-d-oxide structure (Pt/H0.35WO3/TiO2/C, Pt/HxNbO3/TiO2/C), have for the first time been synthesized by the sol-gel methods and shown rather high stability, electron conductivity and non-exchanged initial pure mono-bronze spillover and catalytic properties. The underpotential spillover double layer (DL) charging and discharging properties of the primary oxide (M-OH), interrelated with the interactive self-catalytic effect of dipole-oriented water molecules, has also been proved and pointed out as the phenomenological appearance and aspect of the interactive spillover featuring intermediates. In fact, phenomenological aspects of spillover for the main reacting intermediate species in oxygen and hydrogen electrode reactions along with earned and withdrawn theoretical knowledge represent the basic concepts and aims of the present study.
Highlights
Šta bi onda u suštini podrazumevao i značio jedan takav membranski prenosni mehanizam, koji u anodnom smeru rezultuje pojavom prelivanja primarnih oksida? U tom smislu najpre dolazi do disocijativne adsorpcije molekula vode (jednačina (1-a)) na hypo-d-oksidnim nosačima katalizatora, kao suštinski preduslov da bi potom došlo do uspostavljanja neometanog, ustaljenog i neprekidnog reverzibilnog anodnog membranskog mehanizma odgovarajućih valentnih izmena stanja (W6+ ⇔ W5+ ⇔ W4+ ⇔ W3+ ⇔ W2+ ⇔ W1+, a na srodan način i u slučaju Ti4+, Ta4+ i Nb5+) [12,13,14], naravno sve dok je obezbeđeno neprekidno napajanje dovoljnim količinama vlage i konstantna polarizacija metalnog katalizatora [1,2,3,4,15,16]: WO3 + 3H2O W(OH)6 W(OH)6 + M → W(OH)5+ + M–OH + e
Za razliku od ovakvog uobičajenog potenciodinamičkog spektralnog ponašanja, kontinuirno napajanje zasićenom vodenom parom u struji He na povišenoj temperaturi (80 °C), koje dovodi do kondenzacije (Boudart-ov preduslov za pojavu prelivanja [6,7,8,9]) i naglašeno vlažne strukture mešovitog hipo-d-oksidnog submonosloja, uzetog u svojstvu uzajamno vezujućeg nosača katalizatora, bilo je sada praćeno neuobičajenom pojavom izuzetno velike ekspanzije dvaju reverzibilnih parova strujnih vrhova adsorpcije i desorpcije H-adatoma i Pt–OH
Pt 4f (a) and O1s (b) XPS core level spectra of the Pt catalyst on Nb2O5/C support at room temperature (RT), after annealing under UHV conditions at 360 °C and after reduction at 360 °C under 20% H2 in N2 flow
Summary
Peaks) adsorpcije i desorpcije primarnog oksida (jednačina (1)), svojim savršenim poklapanjem duž potencijalne ose, ispoljavaju naglašeno povratna svojstva izuzetno brzih reakcija, kao osnovni preduslov termodinamičke ravnoteže, pri čemu čitav učinak pojačava prelivanje Pt–OH posredstvom hipo-d-oksidnih nosača, što će biti pokazano odgovarajućim voltamogramima u ovom radu. U širem smislu ovakvih ideja, joni hipo-d-elektronskih vrsta prelazne grupe metala obično ispoljavaju nekoliko valentnih stanja i samim tim omogućuju nastajanje mešovitih uzajamno vezujućih jedinjenja, kao što su, na primer TiO2/WO3, TiO2/Nb2O5 ili TiO2/Ta2O5, i kao takva, dosledno ovde izloženim postavkama i saznanjima, dovode do znatnijeg povećanja samog udela prelivanja, kako H-adatoma, tako isto i primarnih oksida. U stvari, otvoreni aero i zatvoreni kserogeli svojom strukturom predstavljaju dvofazne sisteme, u kojima molekuli rastvarača bivaju nepokretno okruženi (u biti „zarobljeni“) unutar oksidne mreže i takvi materijali se obično razmatraju kao voda-oksidni membranski mikrosastavi [12,13,14]
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