Gas Evolving Electrochemical Systems
Date of Award
Doctor of Philosophy (PhD)
Gas evolving electrochemical systems are widely used in industry, such as in chlorate production, electro-organic synthesis of adiponitrile, and water hydrolysis. These systems contain a very small gap between tall vertical electrodes, where bubbles are formed on one or both of the electrodes at a rate proportional to the local current flux. Once formed, bubbles accumulate in the channel. At steady state, they follow the liquid flow and vacate the channel in a region close to the electrode - in a bubble layer. The gas accumulation within the channel has two drawbacks: First, the Ohmic potential drop is increased with increased gas hold-up, which requires higher average cell potential to run the electrochemical reactions at desired rate. Second, the increased gas hold-up at the upper sections of the channel results in lower utilization of these sections and uneven electrode wear. To overcome these problems, evacuation of gas from the channel is promoted by either forcing the electrolyte flow or designing the system to amplify gas-lift effects. Both of these approaches have been utilized effectively in industrial practice.
The research presented in this dissertation is motivated by the importance of understanding the fundamental causes of inefficiencies in gas evolving electrochemical systems. The thesis focuses on understanding the formation and role of the bubble layer, explores modeling possibilities and evaluates possible experimental methods for model validation. The model is also used to investigate transient operation of electrochemical cells to reduce the gas accumulation in the channel, which might lead to an increase in cell performance and more even current distribution.
Milorad P Dudukovic
Ramesh Agarwal, Pratim Biswas, Renato Feres, Venkat Subramanian