A bird's-eye view for future ionic thermoelectrics: from ions to products

The ionic thermoelectric (i-TE) technology offers a compelling pathway for harvesting low-grade heat, distinguished by its exceptionally high thermopower and inherent material versatility. However, development in this field is constrained by the complex interplay among electrochemical, thermodynamic, and transport phenomena, which poses significant challenges to the fundamental understanding, accurate performance evaluation, and systematic screening of new materials. This review provides a systematic overview and outlook of the i-TE landscape, bridging fundamental principles with future applications. We begin by deconstructing the core components-electrolytes and electrodes-to elucidate the material design strategies that govern the performance. The discussion then progresses to a multi-scale evaluation of key metrics, from intrinsic i-TE properties to device-level energy conversion and storage capabilities. A central focus is placed on dissecting the persistent chemical and physical challenges, including ion selectivity, transport dynamics, and interfacial engineering. This review further surveys the emerging applications of i-TE, ranging from wearable power generation and active cooling to multimodal sensing and integrated multifunctional systems. Furthermore, we highlight the paradigm-shifting potential of synergistic systems, where coupling thermoelectric effects with electrochemical, photocatalytic, or hydrovoltaic processes unlocks unprecedented functionalities and performance enhancements. Ultimately, this review synthesizes current understanding to propose a strategic roadmap for this field. It outlines the key scientific and engineering perspectives on standardization, scalable manufacturing, and reliability that are essential to translate laboratory innovations into viable commercial technologies.