Copper‐Surface‐Mediated Crystallization Engineering of Sp ² Carbon‐Conjugated Covalent Organic Framework for Photoelectrochemical Hydrogen Evolution

Covalent organic frameworks (COFs), are promising candidates for photoelectrochemical hydrogen evolution reaction (PEC HER). In this study, sp 2 ‐c COF photocathodes were synthesized on copper foam via Knoevenagel condensation polymerization, with the crystallinity systematically tuned by varying reaction conditions. By modulation, the alkalinity of the reaction system, crystallinity‐related parameters were optimized, revealing significant variations in the structural integrity of the resulting sp 2 ‐c COFS. Under optimal synthesis conditions (110°C, 30 μL pyridine, 2 days), the photocathode demonstrated a photocurrent density of 60 μA cm −2 at 0.3 V versus RHE, a value 2.5 times higher than that observed for samples with suboptimal crystallinity. These results emphasize the positive impact of increased crystallinity in improving PEC HER performance and provide insights for scalable photocathode design.