Ruthenium-Iridium Nanocrystals Anchored Homogeneously on MOF-Derived Support for Efficient and Stable Oxygen Evolution in Acidic and Neutral Media

Abstract

Achieving efficient and stable oxygen evolution reaction (OER) in acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEM-WE). Supported iridium based nanoparticles (NPs) are the state-of-the-art OER catalysts for PEM-WE, but the non-homogeneous dispersion of these NPs on the support together with their non-uniform sizes usually lead to catalyst migration and agglomeration under strongly corrosive and oxidative OER conditions, eventually causing the loss of active surface area and/or catalytic species and thereby the degradation of OER performance. Here, we design a catalyst comprising surface atomic-step enriched ruthenium-iridium (RuIr) nanocrystals homogeneously dispersed on a metal organic framework (MOF) derived carbon support (RuIr@CoNC), which shows outstanding catalytic performance for OER with high mass activities of 2041, 970 and 205 A gRuIr -1 at an overpotential of 300 mV and can sustain continuous OER electrolysis up to 40, 45 and 90 hours at 10 mA cm-2 with minimal degradation, in 0.5 M H2SO4 (pH = 0.3), 0.05 M H2SO4 (pH = 1) and PBS (pH = 7.2) electrolytes, respectively. Comprehensive experimental studies and density functional theory (DFT) calculations reveal that the good performance of RuIr@CoNC can be attributed, on one hand, to the presence of abundant atomic steps which maximize the exposure of catalytically active sites and lower the limiting potential of the rate-determining step of OER; on the other hand, to the strong interaction between RuIr nanocrystals and the CoNC support which endows homogeneous dispersion and firm immobilization RuIr catalysts on CoNC. The RuIr@CoNC catalysts also show outstanding performance in a single cell PEM electrolyzer, and their large-quantity synthesis is demonstrated.