An acid–base dual-immune Cu electrocatalyst via quaternized chitosan buffering for pH universal nitrate reduction to ammonia

Abstract

Electrochemical nitrate reduction (NO₃RR) presents a promising alternative to the conventional Haber–Bosch process for ammonia production. However, developing highly active and stable catalysts that function effectively in a wide pH range remains a challenge. Copper (Cu) is a high-potential electrocatalyst, but still suffers from low activity and instability across a wide pH range, especially under acidic conditions, hindering practical applications. Herein, we developed an acid–base dual-immune Cu electrocatalyst by in situ decorating cationic quaternized chitosan (QCS) on Cu nanoparticles, which exhibits outstanding NO₃RR activity across a broad pH range, with NH₃ yield rates of 1.4, 0.1 and 0.54 mmol h⁻¹ cm⁻², selectivities of 96.4%, 86.4% and 91.4%, and FEs of 96.3%, 95.8% and 96.1%, under acid, neutral, and alkaline conditions, respectively. Moreover, it demonstrates high NH₃ selectivity and FE over a wide range of NO₃⁻ concentrations, along with robust stability across all pH conditions: >80% FE over ∼550 h in acid, 98.55% FE over 230 h in neutral media, and regenerable stability (∼99% FE over 50 cycles) in alkaline electrolyte following a simple electrochemical treatment. The experimental results reveal that the QCS layer acts as a multifunctional modifier by enriching reactants (NO_x⁻), generating more active sites, and enabling pH-universal protection through a barrier layer, followed by acid-triggered regeneration via reconstruction, which enhances the activity and durability of the Cu catalyst in NO₃RR across a wide pH range. Furthermore, the co-production system for NH₃ and adipic acid shows high combined electron efficiency.