Mesoporous Engineering of Single-Atom Catalyst for Industry-Level Electrocatalytic CO2 Reduction in Membrane Electrode Assemblies.

Atomically dispersed transition metals anchored on nitrogen-doped carbon have emerged as highly promising electrocatalysts for the electrochemical CO2 reduction to CO. However, their industrial-scale application in membrane electrode assemblies (MEAs) is limited by inadequate Faraday efficiency (FE) and long-term stability. Herein, we propose a rational mesoporous engineering approach for Ni-NC catalysts via a two-step space-confinement pyrolysis strategy. Through cryo CO-pulse chemisorption, real-time observations of CO2 gas bubble diffusion, and finite element simulations, we demonstrate that the mesoporous structured Ni-NC (meso-Ni-NC) exhibits significantly enhanced active site accessibility and mass transport capabilities compared to microporous structured Ni-NC (micro-Ni-NC). More importantly, the mesoporous engineering enhances the internal gas-holding capacity of the catalytic layer, effectively mitigating flooding and salt deposition and thus enhancing the catalyst's long-term stability. Consequently, meso-Ni-NC achieves an industrially relevant CO partial current density of 291.8 mA cm-2 at 97.3% CO Faradaic efficiency (FECO), along with stable operation for 136 h at 100 mA cm-2 while maintaining FECO exceeding 90% in an MEA, outperforming those of micro-Ni-NC and representing an advancement over existing state-of-the-art Ni-based single-atom catalysts. This work highlights the critical role of pore structure in determining the performance of industry-level electrocatalytic CO2 reduction.