Enhancement Mechanism of CO2RR toward Methanol on a Ball-Milled CoPc-CNT Electrocatalyst: A Covalent Anchoring Strategy

This study developed a covalent anchoring strategy to synthesize a ball-milled cobalt phthalocyanine-carbon nanotubes (CoPc-CNT) hybrid electrocatalyst for efficient CO₂-to-methanol conversion. The catalyst was systematically characterized using scanning electron microscopy/transmission electron microscopy (SEM/TEM), energy-dispersive spectrometry (EDS), Fourier transform infrared (FT-IR) spectroscopy, UV–vis spectroscopy, Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) to investigate the surface morphology and structure. Then, its electrochemical performance was evaluated through cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), headspace gas chromatography (HS-GC), and proton nuclear magnetic resonance (¹H-NMR), demonstrating a 40% improvement in Faradaic efficiency and an 80% enhancement in partial current density for methanol production compared with its noncovalent counterpart. Mechanistic investigations revealed that covalent grafting synergized with ball milling achieved the optimization of interfacial architecture by enhancing CoPc dispersion on carbon nanotubes (CNT), strengthening π–π electronic coupling, narrowing the band gap, and reducing charge-transfer resistance. Subsequently, the critical reaction steps were accelerated, such as facilitating the initial proton-coupled electron (H⁺/e^–) transfer through increased electroactive Co–N₄ site density, promoting *CO protonation kinetics, and then lowering the energy barriers such as favorable *CH₃OH desorption through redistribution of the highest occupied molecular orbital (HOMO) from CNT to the phthalocyanine macrocycle. Density functional theory (DFT) calculations validated the proposed reaction pathway: *CO₂(g) → *CO₂ → *CO₂^– → *COOH → *CO → *CHO → *OCH₂ → CH₂OH → CH₃OH → CH₃OH(l). This work provides a scalable mechanochemical approach for constructing stable molecular-electrode interfaces and atomic-level insights into how covalent engineering regulates intermediate binding energies and charge-transfer dynamics for selective formation of methanol.