Morphological Evolution of Nanocluster Aggregates and Single Crystals in Alkaline Zinc Electrodeposition

The morphology of Zn electrodeposits is studied on carbon-coated transmission electron microscopy grids. At low overpotentials (η = −50 mV), the morphology develops by aggregation at two distinct length scales: ∼5 nm diameter monocrystalline nanoclusters form ∼50 nm diameter polycrystalline aggregates, and the aggregates form a branched network. Epitaxial (000̅2) growth above an overpotential of |η_c| > 125 mV leads to the formation of hexagonal single crystals up to 2 μm in diameter. Potentiostatic current transients were used to calculate the nucleation rate from Scharifker et al.’s model. The exp­(η) dependence of the nucleation rates indicates that atomistic nucleation theory explains the nucleation process better than Volmer–Weber theory. A kinetic model is provided using the rate equations of vapor solidification to simulate the evolution of the different morphologies. On solving these equations, we show that aggregation is attributed to cluster impingement and cluster diffusion while single-crystal formation is attributed to direct attachment

Electrochemical Desalination of Seawater and Hypersaline Brines with Coupled Electricity Storage

We present a zinc|ferricyanide hybrid flow battery that achieves extensive first-pass desalination while simultaneously supplying electrical energy (10 Wh/L). We demonstrate 85% salt removal from simulated seawater (35 g/L NaCl) and 86% from hypersaline brine (100 g/L NaCl), together with reversible battery operation over 100 h with high round-trip efficiency (84.8%). The system has a high operating voltage (<i>E</i>⁰ = +1.25 V), low specific energy consumption (2.11 Wh/L for 85% salt removal), and a desalination flux (4.7 mol/m²·h) on par with that of reverse osmosis membranes. Salt removal was similarly effective at higher feed salinities, for which reverse osmosis becomes physically impossible because of the pressure required. The results have positive implications for regions that rely on desalination for their freshwater needs, especially where sea salinity is high. Alternatively, the battery may also be useful in minimal liquid discharge wastewater treatment if operated as a brine concentrator