In Situ Construction of Hierarchical CuCo Layered Double Hydroxide Nanoarrays: Synergistic Enhancement and Mass Transfer Intensification in Electrocatalytic Nitrate-to-Ammonia

Abstract

Electrocatalytic nitrate reduction to ammonia provides a sustainable route for nitrate-containing wastewater remediation and energy conversion. The development of nonprecious metal electrocatalysts that simultaneously achieve high ammonia selectivity, fast production rate and long-term stability still remains challenging. This study constructs hierarchical Cu–Co layered double hydroxide nanoarrays directly grown on nickel foam (CuCo LDH/NF) via a facile one-step hydrothermal method. The present work highlights two coupled core innovations: the Cu–Co bimetallic tandem catalytic mechanism and the mass transfer enhancement originating from the interlaced three-dimensional nanoarray architecture. Benefiting from electronic synergistic effect between Cu and Co, a tandem catalytic pathway is formed to suppress intermediate byproduct accumulation. Meanwhile, the in situ grown interlaced nanosheet arrays formed a hydrophilic, hierarchically porous three-dimensional open network. This architecture significantly enlarged the electrochemically active surface area (7.7 mF cm–2) and enhanced mass transfer efficiency. Owing to such dual synergistic optimization of catalytic active sites and mass transfer pathways, the as-prepared CuCo LDH/NF delivers a high NH3 Faradaic efficiency of 96.78% and an NH3 yield rate of 7.8 mg h–1 cm–2 at −0.9 V vs RHE in neutral electrolyte, alongside robust stability over 15 h continuous electrolysis. Kinetic analyses reveal that the nitrate reduction reaction follows an apparent pseudo-first-order model, and the reaction rate constant reaches 0.0521 min–1, which is approximately 23-fold higher than monometallic Co LDH catalyst. Furthermore, the catalyst exhibits good adaptability toward varied nitrate substrate concentrations within a certain range. This work offers a dual-regulation strategy combining electronic-structure modulation and mass-transfer intensification for designing high-performance nitrate-reduction electrocatalysts, and provides experimental insights for practical treatment of nitrate polluted wastewater.