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

## TL;DR

A new catalyst efficiently converts low-concentration nitric oxide into ammonia, offering solutions for air pollution and fertilizer needs.

## Contribution

A chemical strategy to build hollow high-entropy oxides with enhanced electrocatalytic performance for NO reduction.

## Key findings

- RuFeCoNiCuZnO achieves 99.08% Faraday efficiency for NH3 synthesis from low-concentration NO.
- The catalyst outperforms existing materials in both efficiency and production rate.
- Incorporating Ru improves electronic structure and NO adsorption capacity.

## Abstract

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 mgcat
–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 mgcat
–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.