Solid-State K+ Coordination Modulates Electronic Structure of Ni–N3 Single-Atom Catalysts for CO2 Electroreduction

This work demonstrates a strategic shift from dynamic electrolyte modulation to static, intrinsic promotion of the CO2 reduction reaction by stably integrating alkali metal cations as a solid-state component within a heterogeneous catalyst. To address the persistent challenge of alkali metal ion leaching due to high aqueous solubility, we immobilize K+ cations into a carbon nitride framework (Ni@K–C3N4) hosting atomically dispersed Ni–N3 sites via an ionothermal strategy. Structural confinement through coordination with nitrogen sites in the C3N4 matrix effectively suppresses K+ leaching, enabling sustained electronic regulation of the Ni centers. Combined experimental and theoretical analyses reveal that K+ incorporation attenuates d-π conjugation, promotes electron localization around Ni sites, and stabilizes low-valent Niδ+ species. This electronic reconfiguration enhances CO2 adsorption and activation while suppressing competitive hydrogen evolution reaction. The optimized Ni@K–C3N4 catalyst achieves a CO Faradaic efficiency of 95% at −0.74 V vs RHE, a current density of ∼20 mA·cm–2, and stable operation over 50 h. Notably, it maintains >80% CO selectivity under a diluted CO2 atmosphere (40%), highlighting its practicality for real low-concentration streams. This work establishes a polymer-functionalization strategy for precise electronic tuning of single-atom catalysis, advancing the design of efficient CO2 utilization systems.