Study on the effect of hydrogen evolution reaction in the zinc-nickel single flow battery

Considering the conservation laws of mass, momentum, and charge, and further coupling the global reaction kinetics equation and bubble kinetics equation, a two-dimensional transient two-phase flow model of zinc-nickel single flow battery considering hydrogen evolution parasitic reaction is established, which is used to investigate the influence of bubble flow formed by hydrogen bubbles and electrolyte on the battery performance. The accuracy of the model is verified by experimental data, and then the changes of hydrogen volume fraction, hydrogen evolution reaction current density, and negative electrode main reaction current density in the battery with time and space are investigated. Based on further analyzing the influence mechanism of bubble flow on ion transfer at the negative electrode interface, the effects of electrolyte flow rate, applied current density, hydroxide ion concentration, and bubble diameter on hydrogen volume fraction and polarization loss are also studied. The results show that the extra disturbance caused by bubble flow can effectively promote the ion transfer at the negative electrode interface and reduce the concentration polarization and activation polarization loss; On the other hand, it also causes the uneven distribution of ion concentration at the negative electrode interface, which leads to the uneven distribution of current density of hydrogen evolution reaction and negative electrode main reaction at the negative electrode interface. In addition, decreasing electrolyte flow rate, increasing applied current density, increasing hydroxide ion concentration, and increasing bubble diameter can enhance the disturbance effect of bubble flow. For the zinc-nickel single flow battery, this work provides a mechanistic explanation for the influence of the two-phase flow phenomenon caused by hydrogen evolution reaction on battery performance for the first time and lays a theoretical foundation for improving battery cycle life through side reaction management.