Attachment of molecular catalysts onto semiconductor or metal electrodes is a promising approach for rational design of efficient photoelectrochemical cells for solar water splitting and CO2 reduction. The understanding and improvement of such devices requires fundamental understanding of the structure and dynamics of catalysts as well as the interfacial electrolyte environment at electrode-liquid interfaces. Vibrational sum frequency generation (VSFG) spectroscopy is an in situ interface specific technique capable of probing electrochemical interfacial properties at the molecular level. In this talk, we discuss our recent efforts in developing and applying VSFG for studying structural and dynamics of a series of rhenium bipyridyl CO2 reduction catalysts on semiconductor and metal electrodes. We have shown that by combining VSFG experiment with ab initio computational studies, catalyst adsorption geometry can be determined; by IR pump/VSFG probe, ultrafast vibration energy transfer dynamics of the catalyst can be probed with subpicosecond time resolution and sub-monolayer sensitivity; through electrochemical Stark effect, local electric field at the electrode-solution interface can be directly measured; the dependence of interfacial pH on applied bias can be probed; and finally this technique is used to follow surface bound reactive intermediates of CO2 reduction.

In situ vibration sum frequency generation spectroscopic probe of molecular structures and dynamics at electrochemical interfaces

2019 Fall National Meeting

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