Three-dimensional transient model of zinc-nickel single flow battery considering side reactions

Abstract Based on a comprehensive description of the conservation of momentum, mass and charge, as well as the global dynamics involving ion and proton reactions, a three-dimensional transient model for zinc nickel single flow battery considering side reactions of hydrogen evolution and oxygen evolution was established. The accuracy of the model is verified by experiments. The effects of current density, electrolyte flow rate, initial ion concentration, temperature and electrode porosity on the side reactions of hydrogen evolution and oxygen evolution were investigated. The effects of side reactions on the activation polarization and concentration polarization of the battery were studied by comparing the two cases of whether side reactions were considered or not. The results show that the reaction rate of hydrogen evolution and oxygen evolution can be effectively reduced by reducing the applied current density, ambient temperature or increasing the flow rate of electrolyte. Increasing the initial concentration of hydroxyl ions inhibited the occurrence of hydrogen evolution side reactions, but also promoted the occurrence of oxygen evolution side reactions. As the porosity of the positive electrode increases, the reaction rate of the side reaction of oxygen evolution and the oxygen concentration in the positive electrode area gradually decrease. In the later stage of charging, when the shielding effect of oxygen bubbles on the positive reaction interface is not considered, compared with the case without considering the side reaction, the positive electrode activation polarization is larger when considering the side reaction.