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 on 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.

Manganese Oxides (Mn3O4 & α‐MnO2) as Co‐catalysts in Pd‐Based Nanomaterials for the Ethylene Glycol Electro‐Oxidation.

“…BET isotherms of unsupported α‐MnO 2 and Mn 3 O 4 were previously reported [22] . These materials displayed surface areas of 19.91 and 43.74 m 2 g −1 , respectively.…”

“…The percentage of O v with respect O L was of 3.7 and 1.7 % for Pd/α‐MnO 2 and Pd/Mn 3 O 4 , respectively [8] . These percentages were lower to those calculated for pure α‐MnO 2 and Mn 3 O 4 (8.6 and 14.7 %, respectively) [22] . This change together with the shift of Pd 0 3 d core levels from pure Pd to Pd/α‐MnO 2 and Pd/Mn 3 O 4 (Table S5) indicate surface changes, which as before mentioned, can be attributed to the partial growth of noble metal nanoparticles in the oxide surface as reported elsewhere [23] .…”

“…Moreover, the composition between Pd and MnO x was analyzed by EDX, XPS and total reflection X‐ray fluorescence (TXRF) using a Bruker S2 PICOFOX spectrometer operated at 50 kV and 600 μA. Detailed conditions for the different characterizations can be found reported elsewhere [21,22] …”

“…Cyclic voltammograms in KOH were obtained in a three‐electrode electrochemical configuration using glassy carbon plates (1.56 cm 2 ) as working electrodes, the Hg/HgO (1 M NaOH) was used as the reference electrode, and a graphite rod (10 cm length, 10 mm diameter) as the counter electrode. The electrocatalysts were deposited onto the glassy carbon plates through catalytic inks, which were prepared according to a previously reported method [22] . The catalyst loading was controlled to be from 270 to 300 μg cm −2 .…”

“…All reagents were used as received. The MnO x co‐catalysts were prepared using the methodology reported in our previous work [22] . Once obtained the MnO x powders (α‐MnO 2 and Mn 3 O 4 ), the palladium nanoparticles were synthesized through a typical aqueous reduction method.…”