Fabrication of a Scalable Anti-scaling Cathode and an Integrated Device for Extraction of Mg(OH)2 from Seawater

Cathode scaling is a critical bottleneck in direct seawater electrolysis. Although several anti-scaling cathodes have been reported, it is difficult for them to achieve large-scale application due to their small size, high cost, or short lifetime. Herein, a scalable anti-scaling cathode and an integrated device are proposed to demonstrate the practical potential of direct seawater electrolysis. In-situ observations reveal that its stable anti-scaling performance during at least 1000 h is attributed to the surface microstructure, where a thick hydrophobic layer more than 40 μm covers most of Sn microcones in the bottom layer, while only NiFeCo nanocones standing on the tips of Sn microcones are exposed. The essential feature of this hydrophobic hierarchical cone structure is highly dispersed electroactive areas in a stable hydrophobic surface. An integrated device on the basis of this anti-scaling cathode is assembled, and Mg(OH)2 nanoparticles with a purity up to 98.3% are successfully extracted from seawater with an energy consumption of 3.26 kW h kg–1 Mg(OH)2. The stable cell voltage during 1000 h of seawater electrolysis further supports its anti-scaling capability. The novel cathode and integrated device are expected to have application potential in fields such as hydrogen evolution from seawater, softening of reverse osmosis concentrate, and separation of magnesium/lithium from salt lake brine.