August 1, 2016.
The solid-liquid (s-l) interface is the most common interface encountered in electrochemical systems. The s-l interface has wide applications in energy storage, catalysis, and material sciences. In situ studies of chemical reactions taking place on the s-l interfaces can further our understanding of electron transfer and link to real-world device functions under challenging conditions. Direct probing of the solid electrode and liquid electrolyte interface has been realized using a vacuum compatible electrochemical microfluidic reactor, system for analysis at the liquid vacuum interface (SALVI) with time-of-flight secondary ion mass spectrometry (ToF-SIMS). Most recently, the electrochemical version of SALVI was integrated to the synchrotron based single photon ionization mass spectrometry (SPI-MS). SPI-MS has proven to be a versatile technique for analysis of organic species in the solid or gas phase due to its nature of soft ionization. As a practical example, three different lithium polysulfide electrolytes, Li2S4, Li2S6, and Li2S8, were studied under dynamic conditions with various applied voltages. It was found that despite some PDMS interference peaks such as 369 m/z, unique peaks of interest signifying the electron transfer of the LixSy electrolytes can be identified according to the SPI-MS mass spectra. The observation of in situ compositional changes as a result of electrochemical reaction that take place at the s-l interface in a three electrode system allowed us to piece all the fragments together and identify the compound present in the sample at different stages of photoionization energy (PIE) values. Moreover, we demonstrate that liquid SPI-MS technique has been enabled to study dynamic electron transfer of LixSy electrolytes using real-time molecular imaging.
Analytical Chemistry | Chemistry | Engineering | Materials Chemistry | Mathematics | Physical Chemistry
Pacific Northwest National Laboratory (PNNL)
This project has been made possible with support from the National Science Foundation (https://www.nsf.gov), Pacific Northwest National Laboratory (PNNL) and the STAR program.