Impact of Cu Porphyrin Immobilization Modes on Carbon Nanotubes for Selective CO₂ Electroreduction

Immobilized molecular catalysts have demonstrated remarkable performance in the electrocatalytic CO₂ reduction reaction (CO₂RR). However, the impact of different immobilization modes on CO₂ reduction selectivity remains insufficiently explored. Herein, we designed and synthesized three distinct copper porphyrin/carbon nanotubes (CNTs) hybrid materials with varying immobilization strategies, including noncovalent, covalent, and coordination bonding, to explore their effects on catalytic performance and product selectivity. The noncovalently immobilized catalyst predominantly generates C₁ products (CO and HCOOH), achieving a Faradaic efficiency (FE) of 54.6%, with no detectable C₂ products. In contrast, the overall selectivities for C₂ products (CH₃COOH and CH₃CH₂OH) were 39.2% and 65.1% for the covalently and coordinately immobilized catalysts, respectively. These differences in selectivity are primarily attributed to the distinct impacts of immobilization modes on the interaction between the molecular catalyst and the support, which modulate the electronic structure, dispersion uniformity, and the exposure of active sites. This study highlights the critical role of electronic structure modulation through rational molecular catalyst immobilization, offering a strategy to optimize catalytic efficiency and improve product selectivity in CO₂RR.