High‐Entropy Metallene Aerogels: A New Balancer for *H Production and Consumption in Nitrate Reduction Reaction

Abstract High‐entropy metallene aerogels (HEMAs), synergizing high‐entropy metallenes and metallic aerogels, face challenges in achieving single‐phase structures due to multi‐metallic nucleation/growth disparities, hindering two‐dimensional anisotropic growth and three‐dimensional assembly of multi‐component nanocrystals. Herein, the universal preparation of HEMAs was achieved by a seed‐mediated synthetic route for electrochemical nitrate reduction reaction (NO 3 RR). PdCuSnCoNi HEMAs exhibit maximum Faradaic efficiency and yield rate of NH 3 up to 99.5% and 4117.8 µg h −1 mg cat. −1 , surpassing those of Pd metallene aerogels (MAs). In situ attenuated total reflection infrared absorption spectroscopy, online differential electrochemical mass spectrometry and density functional theory calculations reveal kinetic match for *NO 3 to *NO 2 and *NO 2 to *NH 3 , with the energy barrier for *NO 2 formation (potential‐determining step) being lower than that for *H to H 2 , balancing production and consumption of *H and facilitating NH 3 generation on PdCuSnCoNi HEMAs. This study paves the way for efficient NO 3 RR catalysts and guides rational design for diverse electrocatalytic systems.