Phase segregated Cu₂₋ₓSe/Ni₃Se₄ bimetallic selenide nanocrystals formed through the cation exchange reaction for active water oxidation precatalysts

Abstract

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 Ni₃Se₄NCs (sp-Ni₃Se₄) and phase segregated berzelianite Cu₂₋ₓSe (ber-Cu₂₋ₓSe)/sp-Ni₃Se₄ heterostructured NCs as active oxygen evolution reaction (OER) catalysts. A rare sp-Ni₃Se₄ phase was formed by cation exchange of ber-Cu₂₋ₓSe 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₋ₓSe/sp-Ni₃Se₄ heterostructured NCs. The NCs of sp-Ni₃Se₄ and ber-Cu₂₋ₓSe/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.