Surface and Structural Investigation of a MnOx Birnessite-Type Water Oxidation Catalyst Formed under Photocatalytic Conditions.
Catalytically active MnOx species have been reported to form in situ from various Mn-complexes during electrocatalytic and solution-based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnOx catalysts form without supports in situ under photocatalytic conditions. Our most active (4)MnOx catalyst (∼0.84 mmol O2  mol Mn(-1) s(-1)) forms from a Mn4O4 bearing a metal-organic framework. (4)MnOx is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR-TEM as a disordered, layered Mn-oxide with high surface area (216 m(2) g(-1)) and small regions of crystallinity and layer flexibility. In contrast, the (S)MnOx formed from Mn(2+) salt gives an amorphous species of lower surface area (80 m(2) g(-1)) and lower activity (∼0.15 mmol O2  mol Mn(-1) s(-1)). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p3/2 core levels detects enriched Mn(3+) and Mn(2+) content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Benjamin J
BJ
Deibert
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Jingming
J
Zhang
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Paul F
PF
Smith
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (USA).
Karena W
KW
Chapman
Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Sylvie
S
Rangan
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Debasis
D
Banerjee
Department of Material Science & Engineering, University of Texas at Dallas, Richardson, TX 75080 (USA).
Kui
K
Tan
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Hao
H
Wang
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Nicholas
N
Pasquale
Department of Chemistry, Biochemistry, and Physics, Rider University, Lawrenceville, NJ 08648 (USA).
Feng
F
Chen
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
Ki-Bum
KB
Lee
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).|The Waksman Institute, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA).
G Charles
GC
Dismukes
Department of Material Science & Engineering, University of Texas at Dallas, Richardson, TX 75080 (USA).
Yves J
YJ
Chabal
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA). jingli@rutgers.edu.
Jing
J
Li
birnessite structure; manganese oxide; metal-organic frameworks; water oxidation catalyst; water splitting