Heterogenizing\nMolecular Electrocatalysts on a Carbon\nNanotube-Based Hollow Fiber as Selective and Efficient CO<sub>2</sub> Penetrable Electrodes for High-Current-Density CO Electrosynthesis

While\nrecently developed gas-penetrable electrodes (GPEs) have\nwell-addressed the issues of salt precipitation and flooding faced\nby the traditional gas diffusion electrodes (GDEs), most developed\nGPEs are prepared based on the use of high-purity metals with high\nquantity, which limits their mass production and thus practical application\nat scale. Herein, we develop carbon-based GPEs by immobilizing (CoPc)\nmolecular electrocatalyst on the surface of a carbon nanotube-interconnected\nhollow fiber (CoPc/CNTs HF) for the electrosynthesis of CO from the\nelectrocatalytic CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) in aqueous solution. Thanks to the improved CO<sub>2</sub> mass\ntransfer and the abundance of well-established triphasic reaction\ninterfaces enriched with highly active and selective CoPc electrocatalyst,\nthe as-fabricated CoPc/CNTs HF operating under a GPE configuration\ndemonstrates high performance toward the CO<sub>2</sub>RR, and it\nexhibits a maximum partial current density of CO production (<i>j</i><sub>CO</sub>) of 153.4 mA cm<sup>–2</sup> at −0.93\nV vs reversible hydrogen electrode (RHE). Meanwhile, the CO Faradaic\nefficiency (FE<sub>CO</sub>) of CoPc/CNTs HF is beyond 85% over the\nwhole applied potential range (−0.63 to −0.93 vs RHE)\nand achieves the highest value of 96.5% at −0.73 V vs RHE.\nNotably, this CoPc/CNTs HF can maintain stable FE<sub>CO</sub> and <i>j</i><sub>CO</sub> for at least 20 h. This work paves a new\navenue for the development of carbon-based hybrid GPEs with integrated\nstructure and high performance, which would hold promise for various\ngas-involved energy-conversion reactions, such as the nitrogen reduction\nreaction (NRR) and oxygen reduction reaction (ORR).