In-situ X-ray absorption study of evolution of oxidation states and structure of cobalt in Co and CoPt bimetallic nanoparticles (4 nm) under reducing (H2) and oxidizing (O2) environments.
In-situ near edge X-ray absorption fine structure spectroscopy was performed to monitor the oxidation states of Co and CoPt nanoparticles (NPs) of 4 nm size in the presence of H(2) and O(2) in the pressure range of 1 bar and 36 Torr respectively. Platinum helps the rapid reduction of cobalt oxides in hydrogen at a rather low temperature (38 °C). In addition, reversible changes of the oxidation states of cobalt in the Co and CoPt NPs as a function of cycling oxygen pressure (in the range of millitorr to 36 Torr) are quantified and compared. The role of Pt in the process of Co reducing and oxidizing was explored. Our findings permit the prediction of the cobalt oxidation states as the reaction conditions are altered. The experimental results also suggest the presence of tetrahedral structure of Cobalt oxide that differs from the Co(3)O(4) spinel structure.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Fan
F
Zheng
Selim
S
Alayoglu
Jinghua
J
Guo
Vladimir
V
Pushkarev
Yimin
Y
Li
Per-Anders
PA
Glans
Jeng-lung
JL
Chen
Gabor
G
Somorjai
D003035:Cobalt / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D010984:Platinum / Q000737:chemistry*; D013499:Surface Properties; D056928:X-Ray Absorption Spectroscopy / Q000379:methods
D046911:Macromolecular Substances; D003035:Cobalt; D010984:Platinum; D006859:Hydrogen; D010100:Oxygen