Carbon Dots Supported on CuNi Layered Double Hydroxides as Electrocatalysts for Nitrate Reduction

Abstract

The electrochemical nitrate reduction reaction (NO₃RR) offers a green alternate for ammonia (NH₃) synthesis, which is still hindered by the low Faradaic efficiency (FE) and undesired nitrite release, especially upon fluctuating operating conditions. Here, we demonstrate a carbon dot (CD)-coupled CuNi layered double hydroxide (CuNi LDH) interfacial 2D nanoreactor for efficient nitrate reduction with high selectivity and low nitrite (NO₂⁻) release resilient to wide fluctuations owing to the specific stabilization and directional conversion of *NO₂ within the confined interfacial catalytic microenvironment. The intimate coupling between CuNi LDH/CDs enables effective interfacial potential accumulation and charge redistribution, which induces a positive shift of nitrate activation to 0 V vs. RHE and selective stabilization of *NO₂ that fundamentally avoids the immature release of NO₂⁻. In situ spectroscopy and DFT calculations reveal the facilitated *NO₃ to *NO₂ conversion and the lowered barrier for *NH₂OH to *NH₂ (the rate-determining step). The optimized CuNi LDH/CDs in the flow cell maintain NH₃ FEs above 90% and NO₂⁻ residue below 10 ppm over varying potentials, nitrate concentrations, and synthetic simulated industrial wastewater temperatures. This work provides a reliable catalytic system for practical NO₃RR that is resilient to fluctuations and a revolutionizing strategic paradigm for catalyst design in complex environmental catalysis.