Iron-Based Spinel Oxide Nanoparticles for Electrocatalysis of Oxygen Evolution Reaction

The design of cost-effective and highly active, durable electrocatalysts for the sluggish oxygen evolution reaction (OER) is critical for promoting various energy conversion process such as water splitting and rechargeable metal-air batteries. Due to a wider selection of earth-abundance and low cost catalyst candidates (e.g., mixed 3d -transition metal oxides), OER in alkaline environment has attracted considerable interests during past years. Besides the recently developed Ni-Fe layered double hydroxides (LDH) catalysts, spinel phase transition metal oxides have also drawn particular interests owing to their well-defined rigid structure and thus potentially high stability during electrocatalysis. While improved OER activities have been demonstrated, currently most spinel transition metal oxides (mainly Co-based spinel oxides) still underperformed the state-of-the-art benchmark OER catalyst IrO 2 and the Ni-Fe LDH catalysts. Moreover, atomic insights into the surface structure that governs their OER reactivities and stabilities still remain very limited. We report here the exploration of iron-based spinel oxide nanoparticles (M x Fe 3-x O 4 , M= Mn, Fe, Co, Ni, Cu) as a new class of alkaline OER electrocatalysts with potentially both high electrocatalytic activity and high stability. Emphasis will be placed on atomistic understanding on the surface cation chemistry and surface atomic structures of the spinel oxide nanoparticles and their correlations with OER activities and stabilities. This will be achieved by comparative microscopic and spectroscopic studies of the nanoparticle surfaces before and after OER electrocatalysis using high-resolution (scanning) transmission electron microscopy, electron energy loss spectroscopy and X-ray photon spectroscopy, which will be further complemented by density functional theory calculations. The results will provide important insights into the structure-activity-stability relations of spinel phase transition metal oxides as well as other mixed metal oxides for OER electrocatalysts.