Copper-Hydroxyapatite-Carbon Nitride Composite from Covalent Organic Framework (COF) Precursors for Efficient...

The development of efficient and selective electrocatalysts is crucial for the electrochemical reduction of CO₂ into value-added products. We report a carbon nitride-based composite, synthesized via a one-pot assembly of an imine-linked covalent organic framework (CIN-1) with embedded hydroxyapatite (HAP) and a copper-hydroxyquinone complex, followed by thermal annealing (HAP_Cu@CN). Structural and compositional analyses (XRF, XPS, TEM-EDX, Raman, and XRD) revealed intimate contact among copper nanoparticles, carbon nitride, and HAP nanorods. Electrocatalytic tests showed that only copper on carbon nitride (Cu@CN) favored methane formation (FE ≈ 60% at -0.9 V vs RHE, reaching -110 mA cm^-2 as current density), while HAP_Cu@CN selectively produced formate with 60% FE at -1.0 V vs RHE, with a current density of -55 mA cm^-2. The presence of HAP enhanced the availability of CO₂ at the electrode surface via bicarbonate adsorption and suppressed hydrogen evolution, improving product selectivity without compromising current density. These findings highlight the synergistic role of HAP in steering the CO₂ER toward formate production.