Engineering the interface of carbon electrocatalysts at the triple point for enhanced Oxygen Reduction Reaction.

Aqueous oxygen reduction reaction (ORR) has recently received increasing attention due to its critical role in clean and sustainable energy generation technologies, such as Proton Exchange membranes (PEM) fuel cells, alkaline fuel cells and Zn-air batteries. The sluggish kinetics associated with ORR result from multistep electron transfer process. The slow kinetics are partially related to the O2 adsorption process onto the catalyst, which happens at the triple-phase boundary (TPB) of the electrocatalyst-electrolyte-oxygen interface. Hence, tremendous efforts have been devoted to improving the intrinsic properties of electrocatalysts such as active sites, electrical conductivity and porosity. Engineering the electrocatalyst's interfacial properties is another critical issue in ORR, however less encountered and described in the literature. The catalyst's surface provides the microenvironment for the triple boundary interface reaction, which directly influences its electrocatalytic activity and the kinetics. In this minireview we will summarise the existing literature on manipulating the interfacial surface of non-precious metal catalysts at the triple point between the solid catalyst, the aqueous electrolyte and the O2 gas with the aim to improve the ORR efficiency. In this review, we will discuss various approaches towards improving the wettability and nanostructuring the catalyst's surface to boost the activity of the surface-active sites and provide improved stability.