This study aims to clarify the concentration of zincate ions near the zinc anode upon charging. After preliminary experiments in a mini-channel were conducted to identify the system parameters, galvanostatic charging experiments in a zinc battery cell were conducted at current densities of 20 and 40 mA cm~(-2). The bulk concentration of zincate ions is set to 0.49 and 0.98 mol L~(-1). Images near the zinc anode were captured using an optical microscope to calculate the zincate ion concentration distribution through the background oriented Schlieren (BOS) technique. They were taken at an equal time intervals to investigate the transition of the concentration diffusion layer. It was conrmed that the BOS technique enables us to quantitatively measure the zincate ion concentration in zinc anode batteries. The results are consistent with the theoretical expectation. The applied current density basically determines the concentration gradient near the anode surface, although it takes time to reach a steady state. The spatial variance in the zincate ion concentration at the anode surface increases with the distance from equilibrium.
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