<p>The synergistic Cu⁰-Cu⁺ sites is regarded as the active species towards NH₃ synthesis from the nitrate electrochemical reduction reaction (NO₃^-RR) process. However, the mechanistic understanding and the roles of Cu⁰ and Cu⁺ remain exclusive. The big obstacle is that it is challenging to effectively regulate the interfacial motifs of Cu⁰-Cu⁺ sites. In this paper, we describe the tunable construction of Cu⁰-Cu⁺ interfacial structure by modulating the size-effect of Cu₂O nanocube electrocatalysts to NO₃^-RR performance. We elucidate the formation mechanism of Cu⁰-Cu⁺ motifs by correlating the macroscopic particle size with the microscopic coordinated structure properties, and identify the synergistic effect of Cu⁰-Cu⁺ motifs on NO₃^-RR. Based on the rational design of Cu⁰-Cu⁺ interfacial electrocatalyst, we develop an efficient paired-electrolysis system to simultaneously achieve the efficient production of NH₃ and 2,5-furandicarboxylic acid at an industrially relevant current densities (2 A cm⁻²), while maintaining high Faradaic efficiencies, high yield rates, and long-term operational stability in a 100 cm² electrolyzers, indicating promising practical applications.</p>