Ultralow-iridium content NiIr alloy derivative nanochain arrays as bifunctional electrocatalysts for overall water splitting.

The development of low-cost and high-durability bifunctional electrocatalysts is of considerable importance for overall water splitting (OWS). This work reports the controlled synthesis of nickel-iridium alloy derivative nanochain array electrodes (NiIrx NCs) with fully exposed active sites that facilitated mass transfer for efficient OWS. The nanochains have a self-supported three-dimensional core-shell structure, composed of a metallic NiIrx core and a thin (5-10 nm) amorphous (hydr)oxide film as the shell (e.g., IrO2/NiIrx and Ni(OH)2/NiIrx). Interestingly, NiIrx NCs have bifunctional properties. Particularly, the oxygen evolution reaction (OER) current density (electrode geometrical area) of NiIr1 NCs is four times higher than that of IrO2 at 1.6 V vs. RHE. Meanwhile, its hydrogen evolution reaction (HER) overpotential at 10 mA cm-2 (η10 = 63 mV) is comparable to that of 10 wt% Pt/C. These performances may originate from the interfacial effect between the surface (hydr)oxide shell and metallic NiIrx core, which facilitates the charge transfer, along with the synergistic effect between Ni2+ and Ir4+ in the (hydr)oxide shell. Furthermore, NiIr1 NCs exhibits excellent OER durability (100 h @ 200 mA cm-2) and OWS durability (100 h @ 500 mA cm-2) with the nanochain array structure well preserved. This work provides a promising route for developing effective bifunctional electrocatalysts for OWS applications.