Poly(ethylenimine)-assisted synthesis of hollow carbon spheres comprising multi-sized Ni species for CO2 electroreduction

Electrochemical CO₂ reduction to produce value-added chemicals and fuels is one of the research hotspots in the field of energy conversion. The development of efficient catalysts with high conductivity and readily accessible active sites for CO₂ electroreduction remains challenging yet indispensable. In this work, a reliable poly(ethyleneimine) (PEI)-assisted strategy is developed to prepare a hollow carbon nanocomposite comprising a single-site Ni-modified carbon shell and confined Ni nanoparticles (NPs) (denoted as Ni@NHCS), where PEI not only functions as a mediator to induce the highly dispersed growth of Ni NPs within hollow carbon spheres, but also as a nitrogen precursor to construct highly active atomically-dispersed Ni-Nx sites. Benefiting from the unique structural properties of Ni@NHCS, the aggregation and exposure of Ni NPs can be effectively prevented, while the accessibility of abundant catalytically active Ni-Nx sites can be ensured. As a result, Ni@NHCS exhibits a high CO partial current density of 26.9 mA cm^–2 and a Faradaic efficiency of 93.0% at −1.0 V vs. RHE, outperforming those of its PEI-free analog. Apart from the excellent activity and selectivity, the shell confinement effect of the hollow carbon sphere endows this catalyst with long-term stability. The findings here are anticipated to help understand the structure-activity relationship in Ni-based carbon catalyst systems for electrocatalytic CO₂ reduction. Furthermore, the PEI-assisted synthetic concept is potentially applicable to the preparation of high-performance metal-based nanoconfined materials tailored for diverse energy conversion applications and beyond.