This study presents a novel approach to enhance the electrocatalytic reduction of nitrate to ammonia (NH₃) by integrating few-atom-layer metal (FL-M) on high-entropy alloys (HEAs). The researchers developed a 'surface entropy reduction' method to induce the exsolution of a component with weak affinity for others, forming FL-M on the HEA surface. This FL-M, specifically FL-Ag, collaborates with the HEA substrate to serve as geometrically separated active sites for multiple intermediates in the complex reaction. The FL-Ag/HEA catalyst demonstrates outstanding performance for nitrate reduction, achieving a Faradaic efficiency of 92.7%, an NH₃ yield rate of 2.45 mmol h⁻¹ mg⁻¹cat., and high long-term stability (>200 h). The study highlights the precise manipulation of atomic arrangement to expand the chemical space of HEA catalysts and their potential applications. The electrochemical synthesis of chemicals and fuel feedstocks, such as alkanes, alcohols, and ammonia, typically involves multiple electron and proton transfers and competing adsorption of different intermediates. However, a linear correlation among the adsorption energies of different intermediates on the electrocatalyst surface poses a challenge in simultaneously enhancing the electrocatalyst's activity toward all reaction intermediates. This scaling relationship makes it difficult to design electrocatalysts for complex reactions. The study explores the potential of HEAs as electrocatalysts, which have shown promise in catalyzing various electrochemical reactions, including water electrolysis for hydrogen production, carbon dioxide electrolysis to generate hydrocarbons and alcohols, and nitrogen/nitrate reduction for ammonia synthesis. However, the vastness of compositions in HEAs, which is orders of magnitude larger than that of bi- and trimetallic alloys, becomes intractable. The weighted averaging of properties among surface metal atoms drives the convergence of adsorption energies of reactants on these atoms toward a common value, indicating that HEAs obey similar scaling relations to other well-established heterogeneous catalyst systems. The researchers developed a 'surface entropy reduction' approach to break the scaling relationship inherent in conventional HEAs by in situ exsolving FL-M from the surface as new active sites. Specifically, using entropy balancing in an open HEA system, a principal component element with weak affinity for others, for example, silver, can be exsolved on the surface, resulting in the formation of few-atom-layer silver (FL-Ag). These FL-Ag interact with neighboring metal sites on the HEA parent to establish new active-site motifs, which avoid the generally encountered scaling relationships and, therefore, enable highly efficient cascade conversion of nitrate into ammonia. Combined in situ characterizations and first-principles simulations confirm the critical role of FL-Ag in promoting the continuous generation of the NO intermediate and its subsequent reduction over the HEA nearby. ThisThis study presents a novel approach to enhance the electrocatalytic reduction of nitrate to ammonia (NH₃) by integrating few-atom-layer metal (FL-M) on high-entropy alloys (HEAs). The researchers developed a 'surface entropy reduction' method to induce the exsolution of a component with weak affinity for others, forming FL-M on the HEA surface. This FL-M, specifically FL-Ag, collaborates with the HEA substrate to serve as geometrically separated active sites for multiple intermediates in the complex reaction. The FL-Ag/HEA catalyst demonstrates outstanding performance for nitrate reduction, achieving a Faradaic efficiency of 92.7%, an NH₃ yield rate of 2.45 mmol h⁻¹ mg⁻¹cat., and high long-term stability (>200 h). The study highlights the precise manipulation of atomic arrangement to expand the chemical space of HEA catalysts and their potential applications. The electrochemical synthesis of chemicals and fuel feedstocks, such as alkanes, alcohols, and ammonia, typically involves multiple electron and proton transfers and competing adsorption of different intermediates. However, a linear correlation among the adsorption energies of different intermediates on the electrocatalyst surface poses a challenge in simultaneously enhancing the electrocatalyst's activity toward all reaction intermediates. This scaling relationship makes it difficult to design electrocatalysts for complex reactions. The study explores the potential of HEAs as electrocatalysts, which have shown promise in catalyzing various electrochemical reactions, including water electrolysis for hydrogen production, carbon dioxide electrolysis to generate hydrocarbons and alcohols, and nitrogen/nitrate reduction for ammonia synthesis. However, the vastness of compositions in HEAs, which is orders of magnitude larger than that of bi- and trimetallic alloys, becomes intractable. The weighted averaging of properties among surface metal atoms drives the convergence of adsorption energies of reactants on these atoms toward a common value, indicating that HEAs obey similar scaling relations to other well-established heterogeneous catalyst systems. The researchers developed a 'surface entropy reduction' approach to break the scaling relationship inherent in conventional HEAs by in situ exsolving FL-M from the surface as new active sites. Specifically, using entropy balancing in an open HEA system, a principal component element with weak affinity for others, for example, silver, can be exsolved on the surface, resulting in the formation of few-atom-layer silver (FL-Ag). These FL-Ag interact with neighboring metal sites on the HEA parent to establish new active-site motifs, which avoid the generally encountered scaling relationships and, therefore, enable highly efficient cascade conversion of nitrate into ammonia. Combined in situ characterizations and first-principles simulations confirm the critical role of FL-Ag in promoting the continuous generation of the NO intermediate and its subsequent reduction over the HEA nearby. This