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

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.