Abstract
The diminishing finite resources of the earth has prompted scientists and shareholders to explore and study various alternative strategies for energy production. Electrochemical water splitting for simultaneous hydrogen and oxygen gas evolution is considered one of the most promising alternatives as it involves greener methods of harvesting energy and can be operated using renewable energy bias. However, the Oxygen Evolution Reaction (OER) at the anodic chamber of the electrochemical cell is the rate determining step, involving 4e- transfer process against the 2e- process in Hydrogen Evolution Reaction (HER) at the cathode, and the overall water splitting process is kinetically controlled by OER. This is considered a bottleneck in industrializing this promising green hydrogen production technology. Hence, there has been a focus on the fabrication of efficient OER electrocatalysts which could eventually substantiate the HER process for commercialization. Hence, many efficient systems were reported in the literature involving noble and non-noble metal-based oxides. However, so far, a few precious noble metal oxides viz; IrO2, RuO2, PtO2 etc. could give the better OER activity and stability. Hence, search for less expensive, abundant, and efficient OER electrocatalyst is inevitable. The OER process is further challenging when performed using the ‘abundant’ sea-water. The presence of various salt ions, particularly the aggressive chloride ions in sea-water, impedes the performance and make the electrodes more susceptible to corrosion. Therefore, an OER electrocatalyst with good corrosion resistance is highly desired.In this thesis, bimetallic Strontium Cobalt Oxide (denoted as SCO) has been studied and used as electrocatalysts to enhance the OER at the anode. Cobalt oxide shows high electrocatalytic activity analogous to state-of-the-art catalysts and strontium shows good anti-corrosion ability. Bimetallic oxides synergistically combine the good properties of both these metals. So, a series of SCO based electrocatalysts were synthesized with varying Strontium molar percentages, using a sol-gel method with subsequent calcination. All the samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive X-Ray Spectroscopy (EDS/EDX) with mapping to elucidate and confirm the structure, morphology, and elemental composition of the synthesized samples. Results reveal that all the samples were successfully prepared with the desired composition. Lanthanum and Cerium ion doping was also employed in SCO to study the effect on corrosion resistance in sea-water electrolysis. The undoped 5% strontium cobalt oxide showed the least onset potential (1.58V vs RHE) and the least charge transfer resistance (Rct) for the limiting OER process which indicates superior OER activity for the sample. It also showed highest electrochemically active surface area and turnover frequency in alkaline saline electrolyte. Further, the 0.5% Ce doped SCO exhibited the lowest Tafel slope (103 mV/dec) and least susceptibility to corrosion as it had the lowest corrosion current in alkaline saline water (-1.04 mAcm-2) which can be attributed to the formation of Ce(OH)4 layer. Further, the 1% La-doped SCO exhibited the lowest corrosion current in non-saline electrolyte (-1.02 mAcm-2) which can be attributed to the formation of La(OH)3 layer. Hence, this study has laid a foundation to the investigation of efficient OER electrocatalysis which could simultaneously synergize the HER process.
Date of Award | Dec 2022 |
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Original language | American English |
Keywords
- Bimetallic spinel oxide
- Alkaline saline water
- Sol-gel technique
- Dopant
- Corrosion resistance