Divyaraj Desai

A Lateral Microfluidic Cell for Imaging Electrodeposited Zinc near the Shorting Condition

The morphology evolution of zinc electrodeposited from alkaline ZnO/KOH is imaged in situ using a microfluidic cell. Working and counter electrodes are in a lateral configuration, separated by a flow channel with a height of 90 m, resulting in quasi-twodimensional zinc layers. At a flow rate of 0.3 cm/s, zinc packing in the channel is highest at a current density just above the transition from porous to dense zinc, i 170 mA/cm 2 . When deposited, compact zinc is approximately 3 times as dense as porous zinc, as determined by image analysis of the layer. The dense mode invariably leads to ramifications and critical growth, causing cell shorting. Greater zinc packing is possible at a flow rate of 3.1 cm/s, although flow rates of this order are impractical for flow-assisted zinc batteries. Ramified zinc tips approach a kinetically limited rate, independent of electrolyte flow rate. Therefore, increased flow rate cannot control critical growth once it begins. Increased flow rate results in a higher density of ramified tips at equivalent cell potential. The zinc deposition reaction has a Tafel slope of 130 mV below 10 mA/cm 2 and 50 mV

Electrochemical-Mechanical Analysis of Printed Silver Electrodes in a Microfluidic Device

Nanoparticulate printed silver is a core material to flexible, printed circuits. Some commercial silvers are of a sufficient purity that one may consider their use in electrochemical power sources and sensors. We establish an iterative rapid prototyping and measuring method, printing electrodes, annealing them under temperature conditions from 210 to 280°C, and cycling them in a microfluidic cell such that the electrolyte becomes the shearing medium. Electrode strength is quantified by the breakage due to generation of gas-phase oxygen at the electrode. This oxygen generation assisted breaking is found to be a function of the amount of oxygen generation only, independent of current density and electrolyte flow rate. Silver cured at 280°C for 60 min had highest strength and required an average of 241.8 mC/mm 2 at electrode rupture; curing at 280°C for 20 min required only 203.8 mC/mm 2 for failure. Silver strength is quantified as an oxidant storage medium in the forms Ag 2 0 and AgO and as a printed reference electrode. Ag and AgO have higher shear strength compared to Ag 2 O. Thus, shear strength of silver oxide electrodes at potentials of 0.15-0.55 V against a printed silver reference depends on the oxidation state.

ELECTRODEPOSITION MODELING USING COUPLED PHASE-FIELD AND LATTICE BOLTZMANN APPROACH

In this paper, a coupled phase-field (PF) and lattice Boltzmann method (LBM) is presented to model the multiphysics phenomenon involving electro-chemical deposition. The deposition (or dissolution) of the electrode is represented using variations of an order-parameter. The time-evolution of an order-parameter is proportional to the variation of a Ginzburg–Landau free-energy functional. Further, the free-energy densities of the two phases are defined based on a dilute or an ideal solution approximation. An efficient LBM is used to obtain the converged electro-static potential field for each physical time-step of the evolution of the PF variable. The coupled approach demonstrates the applicability of the LBM in a multiphysics scenario. The numerical validation for the coupled approach is performed by the simulation of the electrodeposition process of Cu from CuSO4 solution.