New Insights Into Zinc Passivation Through In‐Operando Measured Zincate Concentrations

Abstract

We present a detailed analysis of the behavior of a new zinc‐air flow cell. This system offers several unique insights into the zinc electrochemistry. Due to the constant slurry flow, concentration gradients are completely destroyed every few seconds and therefore negligible and it is possible to take samples from the anode without interrupting the discharge process. To clarify the underlying processes, the potential of the zinc electrode, the zincate concentration (by titration) and the zinc‐particles (by SEM) were analyzed. These measurements offer the unique opportunity to distinguish between thermodynamic and kinetic contributions to the cell voltage. We found, that in this system zinc passivation, is caused by a critical zincate concentration and the steep increase of the cell potential is a kinetic effect, caused by partial passivation. The key factor for passivation, which limits the capacity to 82 mAh gzinc‑1 or 41 mAh gslurry‑1, is the nucleation of ZnO before the critical zincate concentration is reached. This allows capacities of up to 420 mAh gzinc‑1 or 210 mAh gslurry‑1. These results are therefore not only essential for a further increase of the practical capacity of the system but also offer unique insights in the zinc electrochemistry.