Size Effects of Electrocatalysts: More Than a Variation of Surface Area.

The efficiency of electrocatalytic reactions has been continuously improved in recent years due to the great effort in the development of electrocatalysts. A popular strategy is engineering the size of electrocatalysts for better electrochemical performance and lower cost. Nanosized electrocatalysts with high specific surface area have been widely used in state-of-the-art electrochemical devices such as fuel cells. From an engineering aspect, nanosizing electrocatalysts increases the surface area of the electrode and improves the electrode/device performance. Beyond an engineering scope, this perspective highlights the size effects of certain scientific fundamentals in electrocatalytic reactions. The paper summarizes the representative examples in studying the size effects of electrocatalysts and sheds light on the change of intrinsic properties of electrocatalysts caused by the size variation. The size effects of electrocatalysts should be investigated in terms of both engineering and fundamental aspects; that is, the observed activity change is more than a result of surface area variation, and it is interesting to investigate the link between the intrinsic activity and the properties of the catalysts.