Surface reconstruction in amorphous CoFe-based hydroxides/crystalline phosphide heterostructure for accelerated saline water electrolysis.

The CoFeLDH@Ni 2 P electrocatalyst was fabricated via a facile hydrothermal and electrodeposition process. Benefitting from the amorphous/crystalline (a-c) interfaces and modified electronic structure, CoFeLDH@Ni 2 P exhibits remarkable saline water splitting performance, requires cell voltages of 1.56 V to deliver 10 mA cm−2. The strongly negative charge surface and formed PO 4 3− selectively rejects Cl−, endowing its high tolerance in saline electrolytes. [Display omitted] • Amorphous CoFeLDH-crystalline Ni 2 P heterostructures were constructed. • Vertically aligned structure endows CoFeLDH@Ni 2 P with abundant active sites. • Different surface reconstruction behavior for CoFeLDH@Ni 2 P during HER/OER. • PO 4 3− and more negative charge surface improves anti-corrosive properties. Developing electrocatalysts with high activity and robust performance for large-scale seawater electrolysis to produce hydrogen holds immense significance. Herein, a highly active bifunctional electrode composed of amorphous cobalt-iron layered double hydroxides (CoFeLDH) and crystalline nickel phosphide (Ni 2 P) (denoted as CoFeLDH@Ni 2 P), is employed to boost hydrogen production through seawater electrolysis. The strong interface coupling effectively modifies the electronic structure at active sites, thereby accelerating the catalytic reaction kinetics. Impressively, in situ Raman and post-stability analyses demonstrate a unique reconstruction behavior on the CoFeLDH@Ni 2 P electrode. Bimetal co-incorporated NiOOH (CoFe-NiOOH) and Ni(OH) 2 species are formed during the oxygen evolution reaction (OER), while CoFeLDH@Ni 2 P can transform into Ni(OH) 2 species during the hydrogen evolution reaction (HER) process. Furthermore, the highly negatively charged surface selectively rejects Cl− ions by formed PO 4 3−, endowing CoFeLDH@Ni 2 P with excellent tolerance and promising durability in saline electrolytes. Consequently, the CoFeLDH@Ni 2 P electrode exhibits an overpotential of 106 mV for HER at 10 mA cm−2 and 308 mV for OER to achieve 100 mA cm−2 in 1.0 M KOH solution. Additionally, the CoFeLDH@Ni 2 P (+,-) electrolyzer requires a low cell voltage of 1.56 V to deliver 10 mA cm−2 in 1.0 M KOH + Seasalt. This work presents an appealing strategy for the rational design of advanced electrocatalysts with amorphous-crystalline interfaces, which reveals the source of the activity of transition-metal phosphating compounds in saline water electrolysis. [ABSTRACT FROM AUTHOR]