Physical Chemistry Department -

Should electrochemists care about VSF spectroscopy?

Short answer, yes. If you’re still not convinced see Yujin’s invited reference module, In-Situ Probing of Adsorbates at Electrochemical Interfaces with Vibrational Sum Frequency Spectroscopy, just accepted for publication in the Enclyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry ( e-mail for preprint).

What does surface potential do to self-assembled monolayers of photoswitchable molecules?

Tobias and Yujin’s paper trying to answer this question for a SAM formed of spiropyrans has been accepted for publication in Journal of Physics: Condensed Matter. In it they show that if you’d like to build an electrochemical sensor using an electrode covered with a photoswitchable SAM (and, well, of course you’d like to) you need to quantitatively account for the influence of the surface potential on the composition of the photostationary states. For those who need more, the abstract:

Surfaces whose macroscopic properties can be switched by light are potentially useful in a wide variety of applications. One such promising application is electrochemical sensors that can be gated by optically switching the electrode on or o ff. One way to make such a switchable electrode is by depositing a self-assembled monolayer of bistable, optically switchable molecules onto an electrode surface. Quantitative application of any such sensor requires understanding how changes in interfacial field aff ect the composition of photostationary states, i.e. how does electrode potential a ect the extent to which the electrode is on or o ff when irradiated, and the structure of the SAM. Here we address these questions for a SAM of a 6-nitro-substituted spiro[2H- 1-benzopyran-2,2′-indoline] covalently attached through a dithiolane linker to an Au electrode immersed in a 0.1 M solution of Tetramethylammonium hexauorophosphate in Acetonitrile using interface-speci c vibrational spectroscopy. We find that in the absence of irradiation, when the SAM is dominated by the closed spiropyran form, variations in potential of 1 V have little eff ect on spiropyran relative stability. In contrast, under UV irradiation small changes in potential can have dramatic e ects: changes in potential of 0.2 V can completely destabilize the open, merocyanine form of the SAM relative to the spiropyran and dramatically change the chromophore orientation. Quantitatively accounting for these e ects is necessary to employ this, or any other optically switchable bistable chromophore, in electrochemical applications.

ICAVS 9

In an attempt to further evangelize our efforts in femtosecond time resolved electrochemistry, Kramer gave an invited talk at the Ninth International Conference on Advanced Vibrational Spectroscopy (ICAVS9) in Victoria, Canada titled Towards Experimentally Probing the Hydrogen Evolution Reaction on Pt and Au with Femtosecond Time Resolution.

A Summer Visitor

Nick Pant (undergraduate student from McGill University) has arrived to do a summer internship with us (under Julius’ wing) to work on electrochemical characterization of Fe-oxides. His stay is supported through the DAAD Rise Germany program.

Because there are some people who don’t go to the spring DPG meeting…

In a continued attempt to tell as many people as possible about our ongoing activities Yujin went on a China tour giving talks at the Harbin Institute of Technology to chemical engineers on May 15th (Application of Vibrational Sum Frequency Spectroscopy to Study Various Surfaces and Interfaces) and at the State Key Laboratory of Physical Chemistry of Solid Surfaces Xiamen University, on May 18th (Probing Electrochemical Interfaces with Vibrational Sum Frequency Spectroscopy). In pursuit of the same goal Kramer went to Kaiserslautern, because it’s closer,  for this year’s Bunsentagung where he gave a talk on May 26th titled Towards a Femtosecond Resolved View of the Mechanism of the Hydrogen Evolution Reaction on Au.

Our work out and about…

In this year’s spring meeting of the Condensed Matter Section of the DPG (Dresden, March 19-24) Yujin entertained the assembled multitudes with his view of the electrochemical oxidation of gold and out theory collaborator Sergery Levchenko told the world about our view of why CH2 is stabilized at steps on the basal plane of Ruthenium. If you’re interested in gold oxidation stay tuned but if you’d like to know more about CH2 stabilization, well, you’re in luck. Harald’s paper on this very subject is available in Journal of Physical Chemistry C (or by e-mailing us for a reprint).

Paper published in Angewandte Chemie

In a nice bit of news for a Friday afternoon, Yujin’s paper Hydrophobic Water Probed Experimentally at the Gold Electrode/Aqueous Interface” has just been published in Angewandte Chemie. If you’re passionate about water at metal interfaces (and you should be!!!) here’s the abstract:

Quantitative description of reaction mechanisms in aqueous phase electrochemistry requires experimental characterization of local water structure at the electrode/aqueous interface and its evolution with changing potential. Gaining such insight experimentally under electrochemical conditions is a formidable task. The potential-dependent structure of a subpopulation of interfacial water with one OH group pointing towards a gold working electrode is characterized using interface specific vibrational spectroscopy in a thin film electrochemical cell. Such free-OH groups are the molecular level observable of an extended hydrophobic interface. This free-OH interacts only weakly with the Au surface at all potentials, has an orientational distribution that narrows approaching the potential of zero charge, and disappears on oxidation of the gold electrode.

Out and About at Erkner

Lu and Kramer attended the “International Symposium of the CRC 1109: Metal Oxide – Water Systems” in Erkner from February 19 – 22. Kramer gave an invited talk about our continuing effort to understand the molecular level structure (and hydrophobicity) of the α-Al2O3(0001)/liquid water interface and Lu a poster explaining in detail the challenges in collecting optical surface phonon spectra (of the α-Al2O3(1120) surface) in UHV and how she has managed to overcome them.

First (tentative) step in our move to the new building…

The, somewhat, sisyphean task of moving to our new building has begun. The first tentative step in this direction was moving our 8W laser system off the table this Friday, February 24th. This empty spot is where it used to live.