In-situ analysis of the oxygen evolution reaction of nickel based mixed metal oxide using Raman spectroscopy

• Online Access: http://hdl.handle.net/2047/D20323938

One of the main stumbling block for the advancement of energy storage and fuel cells is the availability of inexpensive catalysts for the oxygen evolution reaction (OER) steps involved in the conversion of chemical energy to electrical energy. Today, platinum is the most commonly used catalyst due to its low overpotential. But it is expensive and scarce. Hence, it is more important than ever to develop novel catalyst that can act as a substitute for platinum. Non-Platinum Group Metal [Non-PGM] catalyst can be an ideal replacement. Recent studies indicate that electrocatalysts containing Ni and Fe exhibit high OER activity. Spectroelectrochemical techniques provide us with a unique ability to probe the mechanisms of the electrochemical reactions that occur at the interface between an electrically conducting solid and a polar liquid. Raman Spectroscopy was used to investigate the electrochemical oxygen evolution reaction occurring on the Nickel Mixed Metal Oxides [Ni-MMOs] deposited on the glassy-carbon disk electrode. An in-situ Raman spectroscopic investigation has been carried out to identify the composition of the active phase present on the surface of Ni-MMO deposited electrodes. Current-voltage curves were generated using a galvanostat/potentiostat. The different types of Ni-MMOs tested upon are Plain Ni, Ni-Fe, Ni-Co and Ni-Fe-Co. The experiments were conducted using 532 nm laser. Results demonstrate that heat-treated (HT) samples have a lower wavebumber in a Raman spectra when compared with respective non-heat treated (non HT) samples, except for Ni-Co MMO which is interestingly opposite in characterstics. This may be due to the fact that in all other Ni-MMOs, the surface species are oxidized in the presence of a Fe active site. In other words, OER activity of all Ni-MMOs increases except for Ni-Co. Heat treatment also helps in increasing the OER activity. Among all the Ni-MMOs, HT Ni-Fe-Co/C has the lowest wavenumber which implies that it has the best OER activity. The goal of this thesis is to use Raman spectroscopy in conjunction with electrochemistry to detect and unravel the behaviour of molecules in different oxidation states and to understand substrates and electrochemical electrodes by studying electrochemically active molecules spectroscopically. Raman spectroscopy also provides us with a tool to comprehend the complex charge transfer activity of Ni- based catalysts and opportunities for fine tuning their properties to increase the OER activity and make these electrocatalysts economically viable. One of the main uses will be in doping of NiO semiconducting quantum dots with Co and Fe which should allow us to improve its conduction and valence bands for photochemical applications. In addition, study of these charge transfer effects will aid in the development of higher conductivity Ni-Co supercapacitors, low-cost oxygen evolution electrocatalysts for energy applications such as high performance Zn-air batteries.