Unconventional phase metal heteronanostructures with tunable exposed interface for efficient tandem nitrate electroreduction to ammonia

Tandem catalysis is an effective approach to achieve highly selective and high-rate multi-electron/proton transfer reactions, such as nitrate electroreduction, which are important for various physicochemical and biological processes. However, present tandem catalysts suffer from uncontrollable interface, limited crystal phase, and complex synthesis protocols. Here, we report facile seed-mediated synthesis of unconventional phase 4H/fcc Au−Cu heterostructures with a unique beaded-bracelet nanostructure (BBN). Importantly, the exposed Au/Cu interface density can be continuously tuned by modulating discrete Cu domain density on Au nanowires. As a proof-of-concept application, 4H/fcc Au−Cu BBN demonstrates high catalytic performance in nitrate electroreduction to ammonia, with a yield rate and partial current density of 116.2 mg h^-1 cm^-2 and 1652.0 mA cm^-2, respectively. In-situ and theoretical investigations suggest that the unconventional 4H phase and tandem catalysis between Au and Cu domains account for the superior electrocatalytic performance. Besides, this method can be extended to synthesize other unconventional phase heteronanostructures. © The Author(s) 2025.