Manipulating the coordination dice: Alkali metals directed synthesis of Co-N-C catalysts with CoN4 sites.

Abstract

Nitrogen-coordinated metal sites (MN_x) in metal- and nitrogen-codoped carbon (M-N-C) catalysts offer promising electrocatalytic activity, but selective synthetic design of MN_x sites with specific coordination environments remains challenging. Here, we manipulate the formation statistics of MN_x sites by using sacrifice alkali metals (AM = Li, Na, and K) to form metal vacancy-N_x carbon (AM-MVN_x-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_x sites as the descriptor for MN_x 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_x-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_x formation and open up the possibility for the rational design of complex M-N-C electrocatalysts with well-defined MN_x sites.