Porosity Engineering Within Ni─N─C Hollow Spheres for Ampere‐Level CO 2 Reduction Electrocatalysis

ABSTRACT CO 2 electroreduction typically requires large overpotentials to sustain high reaction rates, which at current densities approaching 1 A cm −2 inevitably intensify competition from the hydrogen evolution reaction (HER), making it difficult to simultaneously sustain high product selectivity (>95%). In this study, hollow Ni─NC (H‐Ni‐NC) was synthesized using nanoscale silica sphere templates and atomic Zn as a sacrificial pore‐former within the carbon shell. The optimized H‐Ni‐NC achieves a current density of −1.0 A cm −2 with over 95% CO Faradaic efficiency in a flow cell. The high performance was attributed to the hollow sphere architecture enriched with gas‐permeable through‐pores. Notably, the Zn dosage selectively modulates the shell through‐porosity, without altering hollow sphere macrostructure or the active‐site structure, thereby enabling a systematic investigation of porosity effects. Finite‐element simulations provide a qualitative framework suggesting a trade‐off between reactant transport and active surface area with increasing porosity in hollow spherical catalysts. This work underscores that engineering of the nanoscale mass‐transport environment surrounding active sites plays a critical role in designing high‐efficiency electrocatalysts.