Potassium Ion Enrichment via Hollow Porous N-Doped Carbon Nanofibers Encapsulating Nickel Nanoparticles Boosts Acidic CO₂-to-CO Electroreduction

Developing advanced electrocatalysts integrated with optimized electrolyte systems is crucial for efficient acidic electrochemical CO₂ reduction, but it remains highly challenging. Here, we present a novel Ni@NCNT/HPNF-3.4 catalyst comprising Ni nanoparticles encapsulated in N-doped carbon nanotubes, which are anchored to hollow porous carbon nanofibers. This hierarchical architecture not only provides abundant active sites but also selectively enriches K+ while effectively inhibiting H+ migration. In a pH = 1.5 phytic acid-electrolyte with 1 M KCl, the Ni@NCNT/HPNF-3.4 catalyst achieves over 99% CO faradaic efficiency across a wide potential range (−0.8 to −1.5 V vs reversible hydrogen electrode). It shows a high single-pass conversion efficiency of 74.2% at a flow rate of 2 sccm. Finite element simulations further confirm the structure-induced K+ concentration gradient, and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy analysis highlights the critical role of the *COOH intermediate stabilization. This catalyst design significantly mitigates carbonate deposition, thereby enhancing both selectivity and the potential for scalability in CO₂ electroreduction.