Ruthenium-iridium-cobalt alloy hollow nanospheres with high lattice strain for efficient oxygen evolution reaction in proton exchange membrane water electrolysis.

Developing Ruthenium-based catalysts with high durability for oxygen evolution reaction (OER) is critical to achieving low-cost proton exchange membrane water electrolysis (PEMWE). Herein, Ruthenium-Iridium-Cobalt alloy hollow nanospheres (RuIrCo HNSs) with an average size of 25.0 nm and an ultra-thin shell thickness of around 4.0 nm were continuously synthesized in the absence of surfactant by a simple sequential reduction process in two vertically distributed static mixers. The RuIrCo HNSs feature a Ru hexagonal close-packed phase with a high lattice strain of 2.3 %, which significantly inhibits the excessive oxidation of Ru and structural collapse during OER. Thanks to these unique characteristics, the RuIrCo HNSs exhibit a low overpotential of 215 mV at 10 mA cm, much better than most of the OER catalysts reported recently. Moreover, a single PEMWE cell with RuIrCo HNSs || Pt/C just needs a cell voltage of 1.45 V to drive 1.0 A cm and operates stably for 100 h. The theoretical calculation further reveals that the introduction of Ir and Co atoms into Ru not only generates the lattice strain but also suppresses the oxidative reconstruction process of Ru and Ir with the improved electron transfer efficiency by the high orbital hybridization of Ir 5d-Ru 4d-Co 3d, enabling the OER to follow the adsorbate evolution mechanism reactive route via a low adsorption energy of *OOH (2.48 eV), consequently enhancing OER of RuIrCo alloy. This work provides a new design for developing next-generation robust OER catalysts for PEMWE.