A Flow-Through Membraneless Microfluidic Zinc–Air Cell

Abstract

In this work, the proof of concept of a functional membraneless microfluidic Zn‒air cell (μZAC) that operates with a flow‒through arrangement is presented for the first time, where the activity and durability can be modulated by electrodepositing Zn on porous carbon electrodes. For this purpose, Zn electrodes were obtained using chronoamperometry and varying the electrodeposition times (20, 40, and 60 min), resulting in porous electrodes with Zn thicknesses of 3.3 ± 0.3, 11.6 ± 2.4, and 34.8 ± 5.1 μm, respectively. Pt/C was initially used as the cathode to analyze variables, such as KOH concentration and flow rate, and then, two manganese‒based materials were evaluated (α‒MnO2 and MnMn2O4 spinel, labeled as Mn3O4) to determine the effect of inexpensive materials in the cell performance. According to the transmission electron microscopy (TEM) results, α‒MnO2 has a nanorod‒like shape with a diameter of 11 ± 1.5 nm, while Mn3O4 presented a hemispherical shape with an average particle size of 22 ± 1.8 nm. The use of α‒MnO2 and Mn3O4 cathodic materials resulted in cell voltages of 1.39 and 1.35 V and maximum power densities of 308 and 317 mW cm-2, respectively. The activities of both materials were analyzed through density of state calculations; all manganese species in the α‒material MnO2 presented an equivalent density of states with a reduced orbital occupation to the left of the Fermi energy, which allowed for better global performance above Mn3O4/C and Pt/C.