In Situ Modulated Nickel Single Atoms on Bicontinuous Porous Carbon Fibers and Sheets Networks for Acidic CO₂ Reduction

Abstract Carbon‐supported single‐atom catalysts exhibit exceptional properties in acidic CO₂ reduction. However, traditional carbon supports fall short in building high‐site‐utilization and CO₂‐rich interfacial environments, and the structural evolution of single‐atom metals and catalytic mechanisms under realistic conditions remain ambiguous. Herein, an interconnected mesoporous carbon nanofiber and carbon nanosheet network (IPCF@CS) is reported, derived from microphase‐separated block copolymer, to improve catalytic efficiency of isolated Ni. In IPCF@CS nanostructure, highly mesoporous IPCF hinders stacking of CS that provides additional fully exposed sites and abundant bicontinuous mesochannels of IPCF facilitate smooth CO₂ transport. Such unique features enable enhanced Ni utilization and local CO₂ enrichment, which cannot be achieved over conventional pore‐deficient and discontinuous porous carbon fibers‐based supports. In situ X‐ray and Infrared spectroscopy coupling constant‐potential calculations reveal the dynamic distortion of the planar Ni−N₄ to an out‐of‐plane configuration with expanded Ni−N bond during operating CO₂ electroreduction. The potential‐driven low‐valance‐state Ni−N₄ possesses enhanced intrinsic electrokinetics for CO₂ activation and CO desorption yet inhibiting hydrogen evolution. The favorable electronic and interfacial reaction environments, resulted from the in situ tailored Ni site and IPCF@CS support, achieve an FE of near 100% at 540 mA cm⁻², a TOF of 55.5 s⁻¹, and a SPCE of 89.2% in acidic CO₂‐to‐CO electrolysis.