Copper‐Surface‐Mediated Synthesis of sp2 Carbon‐Conjugated Covalent Organic Framework Photocathodes for Photoelectrochemical Hydrogen Evolution

Abstract Sp2‐carbon (sp2‐c) covalent organic frameworks (COFs), featuring distinctive π‐conjugated network structures, facilitate the migration of photo‐generated carriers, rendering them exceptionally appealing for applications in photoelectrochemical water splitting. However, owing to the powdery nature of COFs, leaving anchor the sp2‐c COFs powder tightly onto a conductive substrate challenging. Here, we propose a method for preparing photoactive substance‐conductive substrate integrated photocathodes through copper surface‐mediated knoevenagel polycondensation (Cu‐SMKP), this approach results in a uniform and stable sp2‐c COF film, directly grown on commercial copper foam (COFTh‐Cu). The COFTh‐Cu demonstrates a high H2‐evolution photocurrent density of 56 μA cm−2 at 0.3 V vs. RHE, sustaining stability for 12 h. The as‐prepared COFTh‐Cu represents a 4.5‐fold increase in current density compared to traditional spin‐coating methods and outperforms most COF photocathodes without cocatalysts. This innovative copper surface‐mediated approach for preparing photocathodes opens up a crucial pathway towards the realization of highly active COF photocathodes.