High-Entropy Hexagonal-Phase Oxide Hollow Polyhedrons for Highly Efficient Electrocatalytic Reduction of Low-Concentration NO

The electrochemical nitric oxide (NO) valorization strategy reconciles industrial emission mitigation with distributed ammonia (NH₃) production, offering a dual solution for deteriorating urban air quality and fertilizer-deprived agricultural regions. Rational engineering of active sites constitutes the cornerstone for overcoming this catalytic bottleneck. Herein, we report a chemical etching-coordination strategy that enables the precise construction of hollow-architected high-entropy oxides (HEOs) with a nanoporous shell and customizable multimetallic compositions spanning quinary to decenary systems. Employing RuFeCoNiCuZnO as the first HEO catalyst for electrocatalytic low-concentration NO (1 vol %) reduction delivers record-breaking Faraday efficiency of 99.08% and 104.03 μg h^–1 mg_cat^–1 production rate for NH₃ synthesis, outperforming FeCoNiCuZnO and some reported catalysts. The Zn–NO battery with RuFeCoNiCuZnO achieves a power density of 1.18 mW cm^–2 and an NH₃ yield of 69.87 μg h^–1 mg_cat^–1. Experimental results demonstrate that the incorporation of Ru modifies the electronic structure and enhances NO adsorption capacity of FeCoNiCuZnO, thereby promoting NO electroreduction. This work establishes a general method to engineer HEO nanostructures, whose unique configuration offers new possibilities in catalysis and energy conversion. © 2026 The Authors. Published by American Chemical Society