Liquid-state thermocells (LTCs) are emerging electrochemical heat engines for harvesting low-grade thermal energy across small temperature differences. Their practical performance is jointly limited by internal dissipation associated with ionic and electrochemical transport, as well as by external irreversibility arising from finite thermal coupling to the heat source and sink. In this work, a finite-rate thermodynamic framework is developed for LTCs subject to coupled internal and external irreversibilities. The model combines effective thermoelectrochemical transport, a phenomenological asymmetric Joule-heat partition parameter motivated by electrode and interfacial heat effects, and non-ideal thermal contacts, thereby enabling analytical optimization of power output in four representative configurations. Closed-form expressions are derived for the maximum power and the efficiency at maximum power (EMP), together with the admissible operating domain and an equivalent-circuit interpretation. The results show that the thermal impedance ratio governs a transition between externally limited and internally limited regimes. In the externally dominated limit, all configurations recover the Curzon–Ahlborn efficiency, whereas in the internally dominated limit, the asymptotic EMP depends on the side receiving irreversible heat release. When both dominant irreversibilities are located on the hot side, the highest EMP is achieved, while the opposite configuration yields the lowest EMP. These findings provide a thermodynamic benchmark for the LTC architecture and clarify how thermal contact asymmetry and internal heat release pathways should be coordinated to enhance performance in low-grade heat recovery.
Wu et al. (Mon,) studied this question.