Lanthanoid coordination compounds as diverse self-templating agents towards hierarchically porous Fe–N–C electrocatalysts

Abstract

Pore structure is a critical material property of carbon materials, determining their surface area, active site accessibility, wettability, and efficiency of bubble removal. In the self-templating approach to pore design, inorganic particles form inside a carbon during pyrolysis, templating meso- and macropores. This strategy is simple and economic, yet limited by choice of templating elements and by incomplete understanding of carbon-template interactions. We followed the self-templating process of eight lanthanoid coordination compounds (the iminodiacetates of La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Er³⁺, and Yb³⁺), shedding light on the pore structure and the processes that form it. The resulting carbons showed high BET specific surface areas (up to 2700 m² g⁻¹), hierarchical micro-, meso- and macro-porosity, and lanthanoid-imprinted nitrogen moieties that could be transmetalated to yield atomically dispersed Fe–N_x sites. Some of the resulting Fe–N–C materials showed excellent activity towards hydrazine oxidation electrocatalysis, helping to identify several key links between porosity and electrocatalysis, especially the removal of electrode-blocking N₂(g) bubbles. Overall, this detailed investigation expands the toolbox of rational design methods towards rich and useful electrocatalyst porosities.