Reactors with N+1 bipolar electrode. simplified mathematical model

E. R. HENQUÍN

Buenos Aires

Congreso; 20th Topical Meeting of the International Society of Electrochemistry; 2017

International Society of Electrochemistry

Frequently used technologies in large scale reactors for hydrogen production are electrochemical reactors with bipolar electrodes, which have several advantages over reactors with monopolar electrodes. They are also more energy efficient in industrial plants. However they have a very serious drawback: the inevitable parasitic currents flowing in the bypass duct, affecting their performance, and producing undesirable reaction rates distributions on the electrodes.A few years ago, mathematical modelling activities using balance equations of current in a reactor for producing hydrogen with one bipolar electrode, considering a Tafel kinetic on the electrodes, [1] have been developed. Later in [2] a more complex mathematical model was developed, also considering a single bipolar electrode, but using the technique of finite differences to represent the potential distribution in the electrolyte phase. Also, experiments with hydrogen and oxygen evolution to validate the model, in a reactor with electrolyte without movement, have been performed. In electrochemical reactors, primary current distribution establishes itself when the influence of overpotential is negligible. Considering primary current distribution [3], the knowledge of reactors with multiple bipolar electrodes, has been increased. On the other hand, a theoretical work, comparing primary and secondary currents distributions in a reactor with only one bipolar electrode, with recessed electrodes [4] was performed. In this work, it has been shown that secondary currents distributions are more pronounced than the primary, for the cases of industrial importance. In addition, it has made a great contribution in the field of industrial design of these units.In this contribution, a simplified mathematical model, based on [1], considering that the reactor is used for the production of hydrogen and consisting of N-1 bipolar electrodes (where N is the number of reaction compartments), is presented. Tafel and Butler-Volmer kinetics, were taken into account. In the above figures, simulations considering Tafel kinetic are shown. The dimensionless current density distribution on the terminal electrodes does not vary if the number of bipolar electrodes is increased. However distributions in bipolar electrodes become less marked. On the other hand, the fraction of current drained by the bypass ducts increases, but this increase has a limit.With this work, knowledge of the phenomena produced in reactors having multiple bipolar electrodes, mainly in terms of current distributions on electrodes and parasitic currents, has been increased.[1] J Appl Electrochem (2005) 35:1183?1190.[2] J Appl Electrochem (2008) 38:1259?1267.[3] J Appl Electrochem (2007) 37:877?886[4] J Appl Electrochem (2009) 39:1755?1762