No abstract

Synthesis methods to prepare lower transition metal catalysts and specifically Ni for Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy (SHINERS) are explored. Impregnation, colloidal deposition, and spark ablation have been investigated as suitable synthesis routes to prepare SHINERS‐active Ni/Au@SiO2 catalyst/Shell‐Isolated Nanoparticles (SHINs). Ni precursors are confirmed to be notoriously difficult to reduce and the temperatures required are generally harsh enough to destroy SHINs, rendering SHINERS experiments on Ni infeasible using this approach. For colloidally synthesized Ni nanoparticles deposited on Au@SiO2 SHINs, stabilizing ligands first need to be removed before application is possible in catalysis. The required procedure results in transformation of the metallic Ni core to a fully oxidized metal nanoparticle, again too challenging to reduce at temperatures still compatible with SHINs. Finally, by use of spark ablation we were able to prepare metallic Ni catalysts directly on Au@SiO2 SHINs deposited on a Si wafer. These Ni/Au@SiO2 catalyst/SHINs were subsequently successfully probed with several molecules (i. e. CO and acetylene) of interest for heterogeneous catalysis, and we show that they could be used to study the in situ hydrogenation of acetylene. We observe the interaction of acetylene with the Ni surface. This study further illustrates the true potential of SHINERS by opening the door to studying industrially relevant reactions under in situ or operando reaction conditions.

In operando Raman and optical studies have been performed on lithium–sulfur (Li–S) batteries containing carrageenan binder in the sulfur cathode for chemical trapping of the polysulfides (PSs). Three different types of cells were used: coin cells, EL-cell and capillary cells to examine the PS speciation. With the coin cell we confirm the stability and cyclability of the carrageenan based Li–S cells and the improved capacity retention when compared to conventional polyvinylidene fluoride based Li–S cells. With the EL-Cell, the PS speciation at the cathode is documented but only weak evidences of the nucleophilic trapping of the PS are found. The in operando Raman and optical studies on the capillary cell revealed the dissolution and diffusion of the PS in the whole electrolyte volume. We confirm the disproportionation of S4 − into S3 − in the electrolyte. Strong inhomogeneous PS concentration in the electrolyte are found to develop in the course of the cell charge–discharge cycling which must be detrimental to the performances of the battery.