Ruoxi Wu

A binder-free Co₃O₄ nanoneedle electrode grown directly on nickel foam (Co₃O₄@NF) was fabricated by hydrothermal synthesis followed by calcination and evaluated for electrocatalytic nitrate reduction to ammonium. The integrated three-dimensional architecture combines the catalytic activity of Co₃O₄ with the high conductivity and open porosity of nickel foam, thus exposing abundant active sites, shortening electron-transfer pathways, and facilitating mass transport. Among the electrodes prepared at different calcination temperatures, Co₃O₄@NF calcined at 400 °C delivered the best performance. Under the optimal conditions of −1.4 V vs. Ag/AgCl, pH 7, and an initial NO₃⁻-N concentration of 50 mg L⁻¹, the electrode achieved 83.4% nitrate removal within 480 min together with 98.7% ammonium selectivity. Electrochemical measurements revealed a markedly enlarged electrochemically active surface area and reduced charge-transfer resistance after Co₃O₄ loading. Mechanistic analyses via TBA quenching experiments and DFT calculations revealed that both the direct pathway and the hydrogen-assisted indirect pathway were operative, with the indirect pathway being dominant due to its lower free energy barrier while maintaining negligible nitrite accumulation. The electrode also showed good cycling stability and retained high ammonium selectivity in real water matrices. These results demonstrate that binder-free Co₃O₄ nanoneedles supported on nickel foam constitute a promising cathode architecture for coupling nitrate removal with ammonia recovery.

A binder-free Co₃O₄ nanoneedle electrode grown directly on nickel foam (Co₃O₄@NF) was fabricated by hydrothermal synthesis followed by calcination and evaluated for electrocatalytic nitrate reduction to ammonium. The integrated three-dimensional architecture combines the catalytic activity of Co₃O₄ with the high conductivity and open porosity of nickel foam, thus exposing abundant active sites, shortening electron-transfer pathways, and facilitating mass transport. Among the electrodes prepared at different calcination temperatures, Co₃O₄@NF calcined at 400 °C delivered the best performance. Under the optimal conditions of −1.4 V vs. Ag/AgCl, pH 7, and an initial NO₃⁻-N concentration of 50 mg L⁻¹, the electrode achieved 84.3% nitrate removal within 480 min together with 98.7% ammonium selectivity. Electrochemical measurements revealed a markedly enlarged electrochemically active surface area and reduced charge-transfer resistance after Co₃O₄ loading. Mechanistic analyses further suggested that nitrate reduction on Co₃O₄@NF proceeded predominantly through an indirect pathway while maintaining negligible nitrite accumulation. The electrode also showed good cycling stability and retained high ammonium selectivity in real water matrices. These results demonstrate that binder-free Co₃O₄ nanoneedles supported on nickel foam constitute a promising cathode architecture for coupling nitrate removal with ammonia recovery.

Excessive levels of heavy metal pollutants in the environment pose significant threats to human health and ecosystem stability. Consequently, the accurate and rapid detection of heavy metal ions is critically important. A AgNPs@CeO2/Nafion composite was prepared by dispersing nano-ceria (CeO2) in a Nafion solution and incorporating silver nanoparticles (AgNPs). The morphology, microstructure, and electrochemical properties of the modified electrode materials were systematically characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and cyclic voltammetry (CV). By leveraging the oxygen vacancies and high electron transfer efficiency of CeO2, the strong adsorption capacity of Nafion, and the superior conductivity of AgNPs, an AgNPs@CeO2/Nafion/GCE electrochemical sensor was developed. Under optimized conditions, trace Pb2+ in water was detected using square wave anodic stripping voltammetry (SWASV). The sensor demonstrated a linear response for Pb2+ within the concentration range of 1–100 μg·L−1, with a detection limit of 0.17 μg·L−1 (S/N = 3). When applied to real water samples, the method achieved recovery rates between 93.7% and 110.3%, validating its reliability and practical applicability.

A core–shell metal–organic framework (MOF) based electrochemical sensor (Ag/ZIF-8@ZIF-67) capable of detecting 2,6-DCNP is prepared, with a broad linear response range (R² = 0.992) from 240 nM to 288 μM and a low detection limit of 20 nM.