The Role of Ceria in a Hybrid Catalyst toward Alkaline Water Oxidation.

Ceria-based catalysts for the oxygen evolution reaction (OER) have received keen interest in recent years owing to their potential excellent cost performance. However, despite a flurry of research activities, the mechanism on how ceria activates those hybrid catalysts is still puzzling. Herein, by controllably modifying the oxidation state of Ce in ceria, it was revealed that creating Ce3+ species, which are redox-coupled to Ce4+ under OER conditions, could enhance the conductivity and optimize the OH* binding, leading to greatly improved OER activity of the catalysts. More importantly, the ceria-based hybrid catalysts also exhibited excellent long-term stability even when operating at a high current density of 50 mA cm-2 in the strong alkaline electrolyte of 6 m KOH for more than 50 h. This work unveils the underlying role of ceria in improving the activity/stability of ceria-based catalysts and opens the way to design and fabricate ceria-based electrocatalysts for water splitting.