X-to-Chemical Energy Conversion Efficiency: A Unified Thermodynamic Definition.

X-to-chemical energy conversion efficiency (XTC efficiency, where X refers to thermal, electrical, and solar, etc., as well as the combinations of more than one of them) is an important metric for comparisons between various technologies in the chemical sector, so its definition is fundamental. However, conceptual issues still exist in the definition. Here, we establish a unified definition and apply it in the fields of thermo- and electrochemistry where conventional definitions vary. Particularly, this unified definition can delineate the energy level of the input energies. We further propose the concept of thermodynamics ideality, defined as the ratio of measured XTC efficiency to the corresponding thermodynamic limit; it tells the potential for improvement of chemical systems. This Viewpoint thus encourages the communities to report XTC efficiency using our established definition, to report thermodynamics ideality alongside, and to turn their attention to the investigations in the thermodynamic limit for cutting-edge chemical technologies.