Size-dependent pyrolysis pathways of Co-triazolate MOFs tailor carbon-matrix morphology and catalytic site distribution

The pyrolysis of metal-organic frameworks (MOFs) provides a promising route to synthesize efficient metal-N-C electrocatalysts. While most studies emphasize the metal component, here we focus on how precursor crystal size dictates the pyrolysis pathway and carbon matrix formation mechanism in Co-triazolate MOFs. By precisely controlling precursor size, we uncover two distinct transformation routes: small crystals decompose earlier, releasing acetylene that is catalytically converted by newly formed Co nanoparticles into 1D carbon nanofibers. Due to the higher decomposition temperature of large precursor crystals, this fiber-growth pathway was suppressed, leading to 3D carbon frameworks with Co nanoparticles uniformly encapsulated by graphitic layers. This size-dependent decomposition and ligand-metal interaction establishes a direct link between the precursor size, pyrolysis pathway, and final product. Benefiting from uniform encapsulation, enriched graphitic-N, and abundant Co-N sites, the 3D carbon-supported Co-N-C catalyst exhibits markedly higher hydrogen evolution reaction (HER) performance compared to its 1D counterpart. These findings highlight a pyrolysis-guided strategy for tailoring MOF-derived carbon architectures by shifting focus from metal-ligand coordination to metal-ligand interactions, offering new mechanistic insights and pathways for rational electrocatalyst design.