Driven by the need for improved electric vehicles for transportation and the obvious development of decentralized power grids, fuel cell and battery research is extremely important in materials research today. While fuel cells will play a huge role in distributed power, says Dr. Sanjeev Mukerjee of the Department of Chemistry and Chemical Biology from Northeatern University in Boston, “one huge Achilles heel is its reliance on noble metals.”
Therefore, Dr. Mukerjee shows how the juxtaposition of a synchrotron-based technique (x-ray absorption) and a lab-based Raman spectroscopy provides complementary knowledge of materials. Microscopy and spectroscopy techniques are also important for other energy storage applications. With real-world examples, descriptions of the environmental setups, and explanation of subtractive techniques to assess only surface properties, this webinar is an example-based primer for any researcher interested in using spectroscopy to complement their fuel cell research.
The webinar is presented in two parts: the first discusses the fundamental understanding of electrode properties and the second involves the making of next-generation battery materials.
In both sections, various spectroscopy techniques are used, including synchtrotron-based methods like XANES and EXAFS and lab based methods, specifically Raman spectroscopy.
XAS “is a very effective tool to study nanoparticles because we don’t need any long-range or crystalline character in our catalyst,” Dr. Mukerjee states. One drawback of the technique, though is that some signal does come from the bulk. To remove the signal from the bulk, Dr. Mukerjee’s team uses a subtractive technique to get information only from the chemically active surface.
The complementary tool is in the NUCRET facility, which includes the Raman microscope capabilities of a Thermo Scientific™ DXR2xi Raman microscope, an in-situ battery cell designed to interface with the DXR2xi system, and the OMNIC software.
Battery storage is all about energy density, and Dr. Mukerjee showed examples of the study of lithium-air batteries. “Lithium-air battery, which would actually be the future batteries because it has thousands of time higher energy density compared to the lithium ion battery.” Lithium interacts with oxygen in various states, and Raman was used to study the electro catalysis of non-aqueous air cathodes.
Dr. Mukerjee reviews how molecular spectroscopy when conducted in situ and in operando has unprecedented ability to reveal catalytic pathways and degradation modes, leading to new materials synthesis, which may enable the replacement of noble metals in fuel cells.
An extremely important surface area in a battery is the solid electrolyte interface (SEI) layer that protects the carbon. Comparing X–ray absorption spectrometry (which looks at the short range properties) results with XRD spectroscopy (which looks at long range properties) becomes a very powerful technique to study how lithium goes in and out of the lattice. He then goes on to describe a multi-lithium redox center, which is a very rich materials science case.
Spectroscopy is “critical in understanding how far the battery should be charged or discharged without breaking the host lattice, thereby avoiding any structural degradation.” He also notes that surface-enhanced Raman spectroscopy is also effective for these measurements.”