Numerical Calculation of Ionic Mass-Transfer Rates Accompanying Anodic Zinc Dissolution in Alkaline Solution

Abstract

Transient ionic mass-transfer rates during the anodic dissolution of an upward-facing horizontal zinc electrode in a 10 wt % (1.95 M) KOH aqueous electrolyte were monitored by holographic interferometry. The anode potential during zinc dissolution was also measured against a HgO/Hg reference electrode. A two-dimensional mathematical model, wherein a supporting electrolyte also takes part in the electrochemical reactions, was developed to characterize the electrolyte transport phenomena. Transient mass-transfer rates of both Zn(OH)42− and OH− ions were numerically analyzed, and calculated transient refractive index profiles and anode overpotentials were compared to measured values. The electrochemical dissolution and passivation phenomena of the zinc anode in an alkaline electrolyte solution were discussed.

Coupling Phenomena between Zinc Surface Morphological Variations and Ionic Mass Transfer Rate in Alkaline Solution

“…It is thus expected that ZnO would primarily precipitate near the separator. In our previous paper, 23 the peak current density is recorded at about 10% of the Zn electrode length away from the edge nearest to the counter electrode for a cell without a polyolefin separator. The difference of current density distribution between the previous and present studies indicates that the mass transfer characteristic of an electrolyte solution associated with transport properties of the separator significantly affects the shape of current density distribution.…”

“…22,23 Briefly, an electrochemical cell was fabricated from an acrylic plate, and a 99.99% zinc plate was used as the working electrode. The Ni(OH) 2 /NiOOH counter electrode was charged to 50-80% state of charge before cell discharge.…”

“…The above-described 2D mathematical model was solved numerically by using the finite differences method and deterministic relaxation techniques. 23 The physical properties used in the numerical calculations are listed in Table II. Figure 3 shows the transient variation in calculated anode surface concentrations of both Zn(OH) 4 2− and OH − ions at x = 0.1, 4, and 7.9 mm along the Zn anode at i ave = 20 mA/cm 2 in 1.95 M KOH electrolyte.…”

“…An electrochemical cell with a horizontal upward-facing Zn anode nearby a plan-parallel Ni(OH) 2 /NiOOH electrode has been used frequently in order to suppress the natural convection induced by buoyancy forces. [22][23][24][25] Eisenberg pointed out the importance of natural convection and diffusion under gravity field effects. 26 We also recognized natural convection was very important, especially considering the use of a secondary battery for large-scale storage in an electrical energy network system.…”

An Effective Electrodeposition Mode for Porous MnO2/Ni Foam Composite for Asymmetric Supercapacitors

“…Transition metal oxides and conducting polymers are commonly used as electrode materials for pseudocapacitors [ 8 , 9 , 10 ]. Based on the pseudocapacitive energy storage mechanism, metal oxides/hydroxides, such as TiP 2 O 7 [ 11 ], NiO/RuO 2 [ 12 ], LiTi 2 (PO 4 ) 3 [ 13 ], and Nb 2 O 5 [ 14 ], and metal nitrides MN (M = Cr, Co) [ 15 ], MgCo 2 O 4 [ 16 ], and Zn(OH) 2− –4Zn(OH) 4 2− [ 17 ] can provide higher specific capacitance than that provided by conventional carbon materials and better cycling stability than that of polymer materials. By incorporating carbon materials and transition metal oxides in an asymmetric supercapacitor, the capacitance of a supercapacitor can be significantly enhanced [ 18 ].…”