Map of the Month – Electrochemical Operando Raman Microscopy

Key Points 

• In situ and operando Raman microscopy has become an essential tool for studying electrochemical processes and characterising constituent materials in batteries, fuel cells, and electrolysers. 

• It requires a Raman microscope, an electrochemical cell, and a potentiostat.  

• The RMS1000 Confocal Multimodal Microscope was used to monitor changes in the chemical composition of a water-splitting electrocatalyst during electrode cycling.  

Welcome to Edinburgh Instruments’ blog celebrating our work in Raman, Photoluminescence, and Fluorescence Lifetime Imaging. Every month, we aim to highlight our pick for Map of the Month to show how our Raman and fluorescence spectrometers can be used to reveal all the hidden secrets in your samples.  

August 

In situ and operando Raman microscopy has become an essential tool for studying electrochemical processes and characterising constituent materials in batteries, fuel cells, and electrolysers. The technique can be used to determine the chemical composition of electrodes, electrolytes, and ion exchange membranes, which is invaluable because it allows for an understanding of the chemistry underpinning the overall electrical performance of a system to be gained. The experimental setup to perform electrochemical in situ or operando Raman microscopy requires the following components: 

• A Raman microscope: this includes the monochromatic laser source for exciting the sample during the electrochemical performance, the spectrometer for recording the scattered light, and a confocal microscope for focusing the laser on the region of interest and blocking out-of-focus scattered light.  

• An electrochemical cell: this typically contains a three-electrode system (working electrode, counter electrode, and reference electrode) and a transparent window to allow light to pass in and out. It is placed underneath the objective of the Raman microscope, usually on a motorised stage, to allow for high-spatial-resolution targeting of the sample.  

• A potentiostat: this controls the potential of the electrodes in the electrochemical cell and allows for the potential to be changed between Raman measurements.  

In this Map of the Month blog, we touch on our recent Research Highlight, in which we reviewed a paper from the group of Professor Jingshan Luo at the Solar Energy Research Centre at Nankai University. In it, the RMS1000 Confocal Multimodal Microscope was used for the operando characterisation of a NiFeP_x water-splitting electrocatalyst. By coupling the RMS1000 with a three-electrode cell (with the catalyst operating as the working anode) and measuring the Raman spectra of their catalyst with variable potential, they were able to determine changes in the catalytic active sites that explained the performance of the catalyst during the oxygen evolution reaction.  

The image above shows a map of the changing Raman signatures with increasing potential. Between open circuit potential (OCP) and 1.4 V, the spectra recorded from the electrode show signatures that indicate the presence of Ni²⁺, P, and Fe through their surface bonds with oxygen (shown in red). However, at 1.5 V and above, these spectral signatures are diminished, and two new bands appeared, which were attributed to Ni³⁺-O bonds (shown in blue). This indicated that the NiFeP_x was unstable and being converted to NiFe-layered double hydroxide (LDH) and provided a mechanistic explanation for why NiFeP_x did not outperform NiFe-LDH for oxygen evolution reaction efficiency.  

If you are interested in finding out more about this research and how the Edinburgh Instruments RMS1000 and RM5 Microscopes can be used for electrochemical research, please check out our Research Highlight and the original article, published in the Royal Society of Chemistry Journal of Materials Research A.