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Molecular catalysis that transpires only when the complex is heterogenized: Studies of a hydrogenase complex surface-tethered on polycrystalline and (1 1 1)-faceted gold by EC, PM-FT-IRRAS, HREELS, XPS and STM

Chmielowiec, Brian and Saadi, Fadl H. and Baricuatro, Jack H. and Javier, Alnald and Kim, Youn-Geun and Sun, Guofeng and Darensbourg, Marcetta Y. and Soriaga, Manuel P. (2014) Molecular catalysis that transpires only when the complex is heterogenized: Studies of a hydrogenase complex surface-tethered on polycrystalline and (1 1 1)-faceted gold by EC, PM-FT-IRRAS, HREELS, XPS and STM. Journal of Electroanalytical Chemistry, 716 . pp. 63-70. ISSN 1572-6657. https://resolver.caltech.edu/CaltechAUTHORS:20140204-101048359

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Abstract

The proton-reduction catalytic activity of two di-iron hydrogenase complexes, [(μ-S_(2)C_(3)H_6)[Fe(CO)_3][Fe(CO)_(2)(PPh_3)] (1) and (μ-S_(2)C_(3)H_6)[Fe(CO)_3][Fe(CO)2(PPh2{(CH2)2SH})] (2), was investigated at polycrystalline and (1 1 1)-faceted Au electrodes in nonaqueous electrolyte. Compound (2) was irreversibly tethered to the surface through the single bondSH group; (1) was present only in the unadsorbed (dissolved) state. No enhancement of the proton reduction reaction was observed with the homogeneous complex. Pronounced catalysis was exhibited by the heterogenized (surface-attached) material. Neither increase nor decrease in activity was observed when unadsorbed complex (2) was added to the solution of the heterogenized catalyst. The conclusion from these observations, that no catalysis transpires unless the subject molecular complex is tethered to the electrode surface, is totally unexpected; it runs counter to conventional wisdom that an untethered homogeneous electrocatalyst, especially one that requires a particular entatic (partially rotated) configuration to complete its function, would invariably perform better than its surface-immobilized counterpart. The heterogenized complex, present at rather low coverages due to its sizable adsorbed-molecule cross section, was further investigated by polarization-modulation Fourier transform infrared reflection absorption spectroscopy (PM-FT-IRRAS), high-resolution electron-energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The electrochemistry (EC) and STM results indicated that the catalytic activity of the immobilized complex is a function of its surface coverage but not of its spatial configuration; the catalytic sites are accessible regardless of the particular arrangement of the pendant active site with respect to the surface. The surface-immobilized complex suffered a non-negligible loss in catalytic activity after the ex situ experiments, perhaps due to (partial) decarbonylation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.jelechem.2013.12.025DOIArticle
http://www.sciencedirect.com/science/article/pii/S1572665713005754PublisherArticle
ORCID:
AuthorORCID
Saadi, Fadl H.0000-0003-3941-0464
Javier, Alnald0000-0002-0306-5462
Kim, Youn-Geun0000-0002-5936-6520
Soriaga, Manuel P.0000-0002-0077-6226
Additional Information:© 2014 Elsevier B. V. Available online 29 December 2013. Special Issue in Honour of Kingo Itaya. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, as follows: Experimental work that involved surface spectroscopy, microscopy and electrochemistry were supported through the Office of Science of the U.S. Department of Energy under Award No. DE-SC0004993; the synthesis and characterization of the di-iron complexes were supported by the National Science Foundation (CHE-0616695) (MYD) and the Texas A&M University-CONACYT program (MPS). The authors would like to thank D. Crouthers for the synthesis work and J. Sanabria-Chinchilla for the initial electrochemical experiments.
Group:JCAP
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
NSFCHE-0616695
Texas A&M University-CONACYT ProgramUNSPECIFIED
Subject Keywords:Hydrogen evolution reaction; HER electrocatalysis by surface-attached di-iron hydrogenase complexes; Surface-immobilization-enabled molecular catalysis; Heterogeneous catalysis with homogeneous complexes; Biologically inspired electrocatalysis
Record Number:CaltechAUTHORS:20140204-101048359
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140204-101048359
Official Citation:Brian Chmielowiec, Fadl H. Saadi, Jack H. Baricuatro, Alnald Javier, Youn-Geun Kim, Guofeng Sun, Marcetta Y. Darensbourg, Manuel P. Soriaga, Molecular catalysis that transpires only when the complex is heterogenized: Studies of a hydrogenase complex surface-tethered on polycrystalline and (1 1 1)-faceted gold by EC, PM-FT-IRRAS, HREELS, XPS and STM, Journal of Electroanalytical Chemistry, Volume 716, 1 March 2014, Pages 63-70, ISSN 1572-6657, http://dx.doi.org/10.1016/j.jelechem.2013.12.025. (http://www.sciencedirect.com/science/article/pii/S1572665713005754)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43640
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:04 Feb 2014 19:03
Last Modified:09 Mar 2020 13:18

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