Hierarchically Ordered Pore Engineering of Carbon Supports with High-Density Edge-Type Single-Atom Sites to Boost Electrochemical CO2 Reduction.

Abstract

Metal sites at the edge of the carbon matrix possess unique geometric and electronic structures, exhibiting higher intrinsic activity than in-plane sites. However, creating single-atom catalysts with high-density edge sites remains challenging. Herein, the hierarchically ordered pore engineering of metal-organic framework-based materials to construct high-density edge-type single-atomic Ni sites for electrochemical CO₂ reduction reaction (CO₂RR) is reported. The created ordered macroporous structure can expose enriched edges, further increased by hollowing the pore walls, which overcomes the low edge percentage in the traditional microporous substrates. The prepared single-atomic Ni sites on the ordered macroporous carbon with ultra-thin hollow walls (Ni/H-OMC) exhibit Faraday efficiencies of CO above 90% in an ultra-wide potential window of 600 mV and a turnover frequency of 3.4 × 10⁴ h^-1, much superior than that of the microporous material with dominant plane-type sites. Theory calculations reveal that NiN₄ sites at the edges have a significantly disrupted charge distribution, forming electron-rich Ni centers with enhanced adsorption ability with ^*COOH, thereby boosting CO₂RR efficiency. Furthermore, a Zn-CO₂ battery using the Ni/H-OMC cathode shows an unprecedentedly high power density of 15.9 mW cm^-2 and maintains an exceptionally stable charge-discharge performance over 100 h.