Bifunctional high-entropy alloys for sensitive nitrite detection and oxygen reduction reaction

Herein, a novel confinement growth strategy was proposed to synthesize nanostructured high-entropy alloys (HEAs) by using the carbon nitride (g-C3N4) as anchoring template and phenolic resin as coating layer. Through the high temperature treatment, the FeCoNiCuMn HEA nanoparticles (NPs) formed uniformly on g-C3N4 and phenolic resin derived two-dimensional (2D) N-doped carbon nanosheets (FeCoNiCuMn/NCNS). Due to the synergistic effects of each metal sites in HEAs, the FeCoNiCuMn/NCNS electrochemical sensors show a very sensitive response to nitrite, with a broad linear response range of 2–1000 μM, a high sensitivity of 553.43 µA mM−1 cm−2, a detection limit of 0.14 μM (S/N = 3), and a rapid response balance at 0.74 V (response time is 1.1 s). FeCoNiCuMn/NCNS exhibits extraordinary stability, favorable anti-interference and reproducibility, and offers good feasibility for the detection of nitrite in water. Besides, the FeCoNiCuMn/NCNS also indicate excellent electrocatalytic activity for ORR application in alkaline medium with a higher half-wave potential (E1/2) of 0.87 V, a lower Tafel slope of 48 mV dec−1 and electron transfer number (n) of approximately 3.9, when compared with the commercial Pt/C (0.85 V and 77 mV dec−1). These results suggest that FeCoNiCuMn/NCNS exhibits promising applications in the nitrite detection and oxygen reduction.