Bypassing thermodynamic immiscibility via electrochemical kinetic atom trapping

Abstract Immiscible elemental pairs can access properties unavailable to equilibrium solid solutions, but conventional synthesis approaches suffer from phase separation and heterogeneity. Here, we establish kinetic atom trapping using ultramicroelectrodes, confining metal-ion reduction to a finite interfacial inventory. Ultrahigh-, ultrashort-current pulses deplete the preferentially reduced ion before radial diffusion replenishes the interface, forcing dissimilar ions to reduce concurrently and kinetically trapping and stabilizing homogeneous immiscible nanoalloys. The strategy produces mixed nanoparticles across diverse atomic combinations, such as Cu–Zn, Cu–Ag, Cu–Fe, Fe–Cr, and Cu–Ni systems. A quantitative pulse window, bounded by Sand’s depletion time and radial-diffusion-mediated replenishment, predicts the current density and pulse duration required for co-reduction. These mechanistic design rules establish a route to metastable immiscible alloys and enable automated exploration of non-equilibrium compositions and properties.