Space Charge, Modulating the Catalytic Activity of Single-Atom Metal Catalysts.

Potential-induced electrode charging is a prerequisite to initiate electrochemical reactions at the electrode-electrolyte interface. The 'interface space charge' could dramatically alter the reaction environment and the charge density of the active site, both of which potentially affect the electrochemical activity. However, our understanding of the electrocatalytic role of space charge has been limited. Here, we separately modulate the amount of space charge (characterized by the areal density, σ) with maintaining the electrochemical potential for the oxygen reduction reaction (ORR) at the same level, by exploiting the unique structural feature of MeNC. We reveal that changes in σ control the ORR activity, which is computationally explained by the inductive polarization of the charge density at the active sites, affecting their turnover rates. To guide catalyst design including the space charge effect, we develop a new descriptor, explaining the activity trend in various metal centers and pH conditions using a single volcano. These findings offer fresh insights into the role of space charge in electrocatalysis, providing a new framework for optimizing catalyst design and performance.