Electron Transfer Across Solid/Liquid Interfaces: Elucidating Elementary Processes from Femtoseconds to Seconds (SOLWET)

Our current global energy economy, largely based on the combustion of hydrocarbons, has increasingly deleterious effects on global climate and environmental quality. An energy economy instead based on the combustion of H₂ largely avoids these problems. However H₂ is rare on the Earth's surface. Depending on where you live most of the elemental hydrogen you see when you look out the window is bound up in water: H₂O. This realization suggests the possibility of making H₂ by splitting water: 2H₂O → 2H₂ + O₂. This reaction is strongly unfavorable, it's just the converse of why the combustion of H₂ is a useful candidate energy reaction, but provided we can drive it with a renewable source of energy, e.g. solar, wind, hydropower, etc, it is a prospective long term solution.

It's also a redox reaction. That is it requires moving electrons between chemical entities and can be written as the sum of two half reactions: the Hydrogen Evolution and Oxygen Evolution Reactions (HER and OER). In practice, if you want to build a water splitting device, solids are required that can donate electrons to and accept electrons from water. Despite decades of effort searching finding such solids, for either half reaction, has proven surprisingly difficult. The premise of SOLWET is that the reason finding such materials has proven difficult is that we lack experimental insight into the mechanism by which electrons move across the solid/liquid water interface (and the correlated chemical change that happens when they do).

SOLWET addresses this challenge by using femtosecond optical pulses to initiate the HER and OER tracking the electron on its journey across the interface, and the structural change that follows in this journey's wake, using nonlinear optical and novel optoelectronic spectroscopies. For the HER half reaction we principally study platinum, the current gold-standard in HER catalysis in acid, with the goal of providing mechanistic insight that rationalizes well established experimental trends in reactivity with electrolyte and surface structure. For the OER we principally study hematite, a promising photoanode material whose optimization hinges on better understanding of the role of surface states in the photoelectrochemistry.

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SOLWET Publications

1) Riko Kiessling, Yujin Tong, Alexander J Giles, Sandy Gewinner, Wieland Schöllkopf, Joshua D Caldwell, Martin Wolf and Alexander Paarmann (2019) Surface Phonon Polariton Resonance Imaging Using Long-Wave Infrared-Visible Sum-Frequency Generation Microscopy, ACS Photonics, 6, 3017-3023

2) G. Zwaschka, Y. Tong, M. Wolf and R. Kramer Campen (2019) Probing the Hydrogen Evolution Reaction and Charge Transfer on Platinum Electrodes on Femtosecond Timescales, ChemElectroChem, 6, 2675-2682

3) Tobias Garling, R. Kramer Campen, Martin Wolf and Martin Thämer (2019) A General Approach to Combine the Advantages of Collinear and Noncollinear Spectrometer Designed in Phase-Resolved Second-Order Nonlinear Spectroscopy, Journal of Physical Chemistry A, 123, 11022-11030

4) Igor Ying Zhang, Gregor Zwaschka, Zhenhua Wang, Martin Wolf, R Kramer Campen and Yujin Tong (2019) Resolving the Chemical Identity of H₂SO₄ Derived Anions on Pt(111) Electrodes: They’re Sulfate, Phys Chem Chem Phys, 21, 19147

5) Martin Thämer, Tobias Garling, R. Kramer Campen and Martin Wolf (2019) Quantitative Determination of the Nonlinear Bulk and Surface Response from alpha-Quartz using Phase Sensitive SFG Spectroscopy, Journal of Chemical Physics, 151, 064707

6) Gregor Zwaschka, Igor Nahalka, Arianna Marchioro, Yujin Tong, Sylvie Roke and R. Kramer Campen (2020) Imaging the Heterogeneity of the Oxygen Evolution Reaction on Gold Electrodes Operando: Activity is Highly Local, ACS Catalysis, 10, 6084-6093

7) Igor Nahalka, Gregor Zwaschka, R Kramer Campen, Arianna Marchioro and Sylvie Roke (2020) Mapping Electrochemical Heterogeneity at Gold Surfaces: a Second Harmonic Imaging Study, Journal of Physical Chemistry C, 124, 20021-20034

8) François Lapointe, Martin Wolf, R. Kramer Campen and Yujin Tong (2020) Probing the Birth and Ultrafast Dynamics of Hydrated Electrons at the Gold/Liquid Water Interface via an Optoelectronic Approach, Journal of the American Chemical Society, 142, 18619-18627

9) Gregor Zwaschka (2021) Shining New Light on Water Electrolysis: Probing Electrolytic Water Splitting on Au and Pt with Micron Spatial and Femtosecond Temporal Resolution, Dissertation in the Faculty of Physics, Freie Universität Berlin, Germany