Phase segregated Cu2-x Se/Ni3Se4 bimetallic selenide nanocrystals formed through the cation exchange reaction for active water oxidation precatalysts.

Control over the composition and nanostructure of solid electrocatalysts is quite important for drastic improvement of their performance. The cation exchange reaction of nanocrystals (NCs) has been reported as the way to provide metastable crystal structures and complicated functional nanostructures that are not accessible by conventional synthetic methods. Herein we demonstrate the cation exchange-derived formation of metastable spinel Ni3Se4 NCs (sp-Ni3Se4) and phase segregated berzelianite Cu2-x Se (ber-Cu2-x Se)/sp-Ni3Se4 heterostructured NCs as active oxygen evolution reaction (OER) catalysts. A rare sp-Ni3Se4 phase was formed by cation exchange of ber-Cu2-x Se NCs with Ni2+ ions, because both phases have the face-centered cubic (fcc) Se anion sublattice. Tuning the Ni : Cu molar ratio leads to the formation of Janus-type ber-Cu2-x Se/sp-Ni3Se4 heterostructured NCs. The NCs of sp-Ni3Se4 and ber-Cu2-x Se/sp-Ni3Se4 heterostructures exhibited high catalytic activities in the OER with small overpotentials of 250 and 230 mV at 10 mA cm-2 in 0.1 M KOH, respectively. They were electrochemically oxidized during the OER to give hydroxides as the real active species. We anticipate that the cation exchange reaction could have enormous potential for the creation of novel heterostructured NCs showing superior catalytic performance.