Self-Assembly of a Rh(I) Complex on Au(111) Surfaces and Its
Electrocatalytic Activity toward the Hydrogen Evolution Reaction
Author(s):
Xiao-Shun Zhou, Zhen-Rong Dong, Hai-Ming Zhang, Jia-Wei Yan, Jing-Xing Gao, Bing-Wei Mao
Journal:
Langmuir
Year:
2007
Volume:
23
Pages
6819-6826
DOI:
10.1021/la062949q
Abstract:
The self-assembly of a Wilkinson type of catalyst molecule, trans-RhCl(CO)(PPh3)2, on Au(111) surfaces and its
electrocatalytic properties toward the hydrogen evolution reaction (HER) are investigated by employing scanning
tunneling microscopy (STM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). The selfassembled monolayers of RhCl(CO)(PPh3)2 are prepared from either dichloromethane or aqueous solutions, but the
ordered structures are observed only in atmospheric conditions after solvents evaporate. In the electrolyte solutions,
disordered yet uniformly sized spherical clusters of individual molecules are observed as a result of the conformational
change of the molecule by the solvation effect of water. The immobilized Rh(I) molecular clusters are electrochemically
stable in a wide potential window and exhibit remarkable electrocatalytic activity toward HER in perchloric acid
solutions. Several comparative experiments involving similar types of immobilized complexes containing Ru(I) and
Ir(I) centers and solution species of RhCl(CO)(PPh3)2 are performed. However, none of them are found to be electroactive
to HER. The Tafel slope of HER on the Rh(I) complex modified Au(111) electrode in 0.1 M HClO4 is determined
to be -0.061 V, which is almost in the middle of those on bare Au(111) (-0.093 V) and Rh covered (θRh ≈ 0.3)
Au(111) (-0.034 V) electrodes. XPS measurements reveal a valence change of Rh(I) to Rh(0), and an oxidative
addition and reductive elimination mechanism is suggested for the enhancement of HER.