Manipulating the coordination dice: Alkali metals directed synthesis of Co-N-C catalysts with CoN ₄ sites

Abstract

Nitrogen-coordinated metal sites (MN<i>_x</i>) in metal- and nitrogen-codoped carbon (M-N-C) catalysts offer promising electrocatalytic activity, but selective synthetic design of MN<i>_x</i> sites with specific coordination environments remains challenging. Here, we manipulate the formation statistics of MN<i>_x</i> sites by using sacrifice alkali metals (AM = Li, Na, and K) to form metal vacancy-N<i>_x</i> carbon (AM-MVN<i>_x</i>-C) templates, which are used to direct the solution-phase formation of CoN₄ sites in Co-N-C catalysts. We build a probability weight function based on the embedding energy of M in MN<i>_x</i> sites as the descriptor for MN<i>_x</i> formation statistics, and we predict that the alkali metals are prone to induce the formation of MVN₄ sites. By coordinating Co²⁺ ions with AM-MVN<i>_x</i>-C templates, we synthesize Co-N-C with CoN₄ sites, demonstrating remarkable oxygen reduction activity in anion exchange membrane fuel cells. These results highlight the statistical thermodynamics of MN<i>_x</i> formation and open up the possibility for the rational design of complex M-N-C electrocatalysts with well-defined MN<i>_x</i> sites.