Second Law Analysis of an Electrochemical Ammonia Production Cell for Hydrogen Storage and Transport

Abstract This article presents a second law analysis of a lithium-mediated electrochemical ammonia production cell with internal thermodynamic irreversibilities attributed to ohmic losses and activation energy. A Tafel analysis is first applied to potentiostatic data from past experimental studies to determine relevant electrochemical parameters of the cell. The predictive thermodynamic model provides an entropy-based perspective to quantify and minimize irreversibilities of the electrochemical cell thereby delineating the optimal regions of operation and improving its overall energy efficiency. The thermodynamic analysis based on the second law is then applied to a lithium-mediated electrochemical ammonia production cell with a high Faradaic efficiency. A formulation for the entropy generation of the cell is developed and calculated across the separate overpotential components attributed to the ohmic losses and the kinetic activation energy barriers of the cell. By considering these overpotential contributions to the overall entropy generation of the cell, the study provides unique insight into the inherent inefficiencies in lithium-mediated electrochemical systems and presents alternative pathways to reduce and quantify irreversible losses. The paper advances the theoretical understanding of electrochemical systems and provides a useful tool for assessing and improving the performance of lithium-mediated electrochemical ammonia production cells with ohmic losses and activation energy barriers.