Advanced trends in Raman spectroelectrochemistry in investigation of catalysts

One of the main issues of contemporary society is the switch to clean energy sources that are not grounded on fossil fuels. This can be achieved through proton exchange membrane water electrolyzer (PEMWE) and polymer electrolyte membrane fuel cell (PEMFC). The first transforms excess renewable energy sources to hydrogen and oxygen, while the latter recombined them back to produce electricity. The reactions of oxygen reduction (ORR in PEMFC) and oxygen evolution (OER in PEMWE) occur on noble metal catalysts but need further studies due to slow kinetics and large overpotentials. While carbon-based supports are good for ORR, much more stable ones are demanded for acidic environment and high temperatures of OER. Consequently, we are working on the development of Ir nanoparticles as catalysts deposited on either TiONx support or nanocomposite support in which TiONx is deposited on reduced graphene oxide (rGO) with a large surface area. The high price and lack of noble materials are suggested to be overcome by layered double hydroxides (LDHs) in the case of an alkaline environment. In the frame of this project proposal we will use Raman spectroscopy to get insight into the structural characteristics of the catalysts and supports that are under investigation in the Laboratory for Electrocatalysis, NIC, and Chair of Inorganic Chemistry, FCCT, University of Ljubljana. First the Raman measurement conditions will be evaluated. This will be followed by studies of activated and degraded materials, initially performed ex situ but then extended to in situ Raman spectroelectrochemical studies. We expect to get insights into the structural changes that occur due to corrosion of supports. Moreover, the oxidation of nanoparticles of catalyst (for instance, Ir to IrO2) is also expected. Systematic fitting procedures are planned, as well DFT calculations. The results will be supported with elemental (EDS, XPS, EELS), microscopic (SEM, TEM), and thermic analyses. In addition, we will develop the Raman spectroelectrochemical approach for the investigation of possibilities for green recycling of noble metals (Au, …) in ionic liquids (ILs). ILs can be used multiple times either as a medium for electrochemical dissolution or re-deposition. We are certain that these electrochemical processes can be followed in situ using Raman spectroscopy.