Materials Electrochemists' Never-Ending Quest for Efficient Electrocatalysts: The Devil Is in the Impurities

This Perspective illustrates how impurities in nanomaterials affect their electrocatalytic properties. The focus is on 1D and 2D nanomaterials, starting with carbon nanotubes, through graphene and transition metal dichalcogenides to black phosphorus, and closing the circle with graphene in 3D-printed materials. Through these examples, we show that detailed materials characterization is paramount prior to assigning catalytic properties to specific functionality. We show that while metallic impurities in nanocarbons and black phosphorus are often a source of perceived electrocatalysis of these materials, the different phase and valency impurities are often sources of electrocatalysis in transition metal dichalcogenides. These impurities should not be viewed negatively because if their amount is controlled, then they become dopants and can be beneficial for the intended applications of these nanomaterials.