∼5-Fold enhancement in the thermoelectric figure of merit of sustainable 3D-CuNi interconnected nanonetworks due to ultralow lattice thermal conductivity

Abstract

The pursuit of efficient thermoelectric materials, particularly those composed of low-toxicity and Earth-abundant elements, has intensified in recent years. This study introduces an approach to increase the thermoelectric properties of CuNi alloys through the synergistic application of two nanostructuring techniques: the incorporation of saccharine into the electrolyte to achieve a crystallite size reduction to 23–26 nm and the utilization of three-dimensional (3D) anodic aluminum oxide (3D-AAO) templates to fabricate nanowire networks. For comparison purposes, we successfully electrodeposited CuNi films, one-dimensional (1D) nanowire arrays, and modulated nanowire arrays, together with 3D-nanonetworks, maintaining a consistent composition of Cu_0.60Ni_0.40 across all samples. Notably, while the electrical conductivity and Seebeck coefficient remained consistent between the nanocrystalline CuNi films and the 3D-nanonetworks, a significant reduction in thermal conductivity was observed, decreasing from 29 W m⁻¹ K⁻¹ for the bulk material to 10.9 ± 1.1 W m⁻¹ K⁻¹ for nanocrystalline films, to 5.3 ± 0.5 W m⁻¹ K⁻¹ for the 3D nanonetworks, and to 4.9 ± 0.6 W m⁻¹ K⁻¹ for free-standing 3D CuNi nanonetworks. This reduction is attributed to enhanced phonon scattering within the 3D architecture together with the nanocrystalline size inside the nanowires. The figure of merit (zT) exhibited an impressive increase of more than four times (4.4) for 3D-CuNi nanonetworks within AAO templates and 4.8 times for free-standing 3D-CuNi nanonetworks, when compared to bulk. Our findings underscore the potential of dual nanostructuring strategies to optimize the thermoelectric performance of environmentally friendly, stable, and abundant materials like CuNi, paving the way for advancements in sustainable energy technologies.