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Title: Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

Abstract

Time resolved X-ray absorption spectroscopy (X-TAS) has been used to study the light induced hydrogen evolution reaction catalyzed by a highly stable cobalt complex, [Ru(bpy)3]2+ photosensitizer and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. XANES and EXAFS analysis of a binary mixture of the octahedral Co(III) pre-catalyst and [Ru(bpy)3]2+ after illumination, revealed in-situ formation of a square pyramidal Co(II) intermediate, with electron transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds followed by its decay in the microsecond timescales. The Co(I) structural assignment is supported by calculations based on density functional theory (DFT). At longer reaction times, we observe the formation of the initial Co(III) species concomitant to the decay of Co(I), thus closing the catalytic cycle. The experimental X-ray absorption spectra of the molecular species formed along the catalytic cycle are modeled using a combination of molecular orbital DFT calculations (DFT-MO) and Finite Difference Method (FDM). These findings allowed us to unequivocally assign the full mechanistic pathway followed by the catalyst as well as to determinemore » the rate limiting step of the process, which consists in the protonation of the Co(I). This study provides a complete kinetics scheme for the hydrogen evolution reaction by a cobalt catalyst, revealing unique information for the development of better catalysts for the reductive side of hydrogen fuel cells.« less

Authors:
;  [1];  [2]; ; ; ; ; ;  [1];  [2];  [3];
  1. Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology, Avinguda Països Catalans 16, 43007 Tarragona, Spain
  2. International Research Center “Smart Materials”, Southern Federal University, 344090 Rostov-on-Don, Russia
  3. Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology, Avinguda Països Catalans 16, 43007 Tarragona, Spain; Departament de Química, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1390809
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 138; Journal Issue: 33
Country of Publication:
United States
Language:
English

Citation Formats

Moonshiram, Dooshaye, Gimbert-Suriñach, Carolina, Guda, Alexander, Picon, Antonio, Lehmann, C. Stefan, Zhang, Xiaoyi, Doumy, Gilles, March, Anne Marie, Benet-Buchholz, Jordi, Soldatov, Alexander, Llobet, Antoni, and Southworth, Stephen H. Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water. United States: N. p., 2016. Web. doi:10.1021/jacs.6b05680.
Moonshiram, Dooshaye, Gimbert-Suriñach, Carolina, Guda, Alexander, Picon, Antonio, Lehmann, C. Stefan, Zhang, Xiaoyi, Doumy, Gilles, March, Anne Marie, Benet-Buchholz, Jordi, Soldatov, Alexander, Llobet, Antoni, & Southworth, Stephen H. Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water. United States. doi:10.1021/jacs.6b05680.
Moonshiram, Dooshaye, Gimbert-Suriñach, Carolina, Guda, Alexander, Picon, Antonio, Lehmann, C. Stefan, Zhang, Xiaoyi, Doumy, Gilles, March, Anne Marie, Benet-Buchholz, Jordi, Soldatov, Alexander, Llobet, Antoni, and Southworth, Stephen H. Tue . "Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water". United States. doi:10.1021/jacs.6b05680.
@article{osti_1390809,
title = {Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water},
author = {Moonshiram, Dooshaye and Gimbert-Suriñach, Carolina and Guda, Alexander and Picon, Antonio and Lehmann, C. Stefan and Zhang, Xiaoyi and Doumy, Gilles and March, Anne Marie and Benet-Buchholz, Jordi and Soldatov, Alexander and Llobet, Antoni and Southworth, Stephen H.},
abstractNote = {Time resolved X-ray absorption spectroscopy (X-TAS) has been used to study the light induced hydrogen evolution reaction catalyzed by a highly stable cobalt complex, [Ru(bpy)3]2+ photosensitizer and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. XANES and EXAFS analysis of a binary mixture of the octahedral Co(III) pre-catalyst and [Ru(bpy)3]2+ after illumination, revealed in-situ formation of a square pyramidal Co(II) intermediate, with electron transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds followed by its decay in the microsecond timescales. The Co(I) structural assignment is supported by calculations based on density functional theory (DFT). At longer reaction times, we observe the formation of the initial Co(III) species concomitant to the decay of Co(I), thus closing the catalytic cycle. The experimental X-ray absorption spectra of the molecular species formed along the catalytic cycle are modeled using a combination of molecular orbital DFT calculations (DFT-MO) and Finite Difference Method (FDM). These findings allowed us to unequivocally assign the full mechanistic pathway followed by the catalyst as well as to determine the rate limiting step of the process, which consists in the protonation of the Co(I). This study provides a complete kinetics scheme for the hydrogen evolution reaction by a cobalt catalyst, revealing unique information for the development of better catalysts for the reductive side of hydrogen fuel cells.},
doi = {10.1021/jacs.6b05680},
journal = {Journal of the American Chemical Society},
number = 33,
volume = 138,
place = {United States},
year = {Tue Aug 09 00:00:00 EDT 2016},
month = {Tue Aug 09 00:00:00 EDT 2016}
}
  • Producing hydrogen through solar water splitting requires the coverage of large land areas. Abundant metal-based molecular catalysts offer scalability, but only if they match noble metal activities. We report on a highly active p-GaInP2 photocathode protected through a 35-nm TiO2 layer functionalized by a cobaloxime molecular catalyst (GaInP2-TiO2-cobaloxime). This photoelectrode mediates H2 production with a current density of ~9"0mA"0cm-2 at a potential of 0"0V versus RHE under 1-sun illumination at pH"013. The calculated turnover number for the catalyst during a 20-h period is 139,000, with an average turnover frequency of 1.9"0s-1. Bare GaInP2 shows a rapid current decay, whereas themore » GaInP2-TiO2-cobaloxime electrode shows« less
  • Trigonal-bipyramidal Co(II) complexes are used for photochemical carbon dioxide (CO 2) reduction with Ru(bpy) 3 2+ as a photosensitizer, tri-p-tolylamine (TTA) as a reversible quencher, and triethylamine (TEA) as a sacrificial electron donor to produce carbon monoxide and dihydrogen. Here, the CO 2 reduction is slow because of the large structural changes, spin flipping in the cobalt catalytic intermediates, and an uphill reaction for reduction to catalytically active Co(0) by the photoproduced [Ru(bpy) 3] +.
  • Temperature-programmed reduction and oxidation (TPR and TPO) have been used to study the state of cobalt and rhodium in a series of Co-Rh/..gamma..-Al/sub 2/O/sub 3/ catalysts. The results show that rhodium enhances the reducibility of part of the cobalt, but that it does not prevent the formation of cobalt aluminate, which is irreducible below 773 K. TPR of the coimpregnated Co-Rh/..gamma..-Al/sub 2/O/sub 3/ catalyst shows a reduction peak at a much lower temperature than that of Co/Al/sub 2/O/sub 3/. This and the slight shift relative to the peak of Rh/Al/sub 2/O/sub 3/ indicates that cobalt and rhodium ions are notmore » far apart after coimpregnation, which explains the easy formation of bimetallic particles during reduction. Passivation (oxidation at room temperature) of the reduced bimetallic catalyst leaves the structure the bimetallic particles largely intact, but cobalt is oxidized to a great extent while rhodium remains metallic. Passivated Co-Rh particles thus consist of a rhodium kernel covered by cobalt oxide. TPR of passivated catalysts also suggests that already in the reduced state the bimetallic particles are surface-enriched in cobalt. A thorough oxidation of the bimetallic catalysts, on the other hand, leads to a restructuring, i.e., the formation of metal oxide particles which are in close proximity.« less