Innovative use of air gap membrane distillation to harvest waste heat from alkaline fuel cell for efficient freshwater production: A comprehensive 4E study

Poor power density of alkaline fuel cell (AFC) resulting from inherent waste heat generation significantly hinders its widespread application. Herein, an innovative hybrid system that combines AFC and air gap membrane distillation is proposed, aiming to enhance the power density via utilizing the waste heat for freshwater generation. Based on the laws of thermodynamics and electrochemical theory, the hybrid system model is formulated to derive performance metrics by quantifying various irreversible losses. The thermodynamic performance, competitiveness, economic viability, and environmental impact of the system are comprehensively discussed through energetic, exergetic, economic, environmental (4E) analyses. Calculations predict that the maximum equivalent output power density permits 63.28% higher than that of the standalone AFC at 353 K. The influencing mechanisms of the AFC operation conditions, air gap thickness, and properties of the porous hydrophobic membrane are clarified to discern potential avenues for further performance improvement. Furthermore, a multi-objective local sensitivity analysis indicates that membrane porosity and coolant solution temperature are the most sensitive factors. The levelized costs study reveals that water and electricity costs over the total lifecycle are 56.89 $m−3 and 0.1012 $kWh−1, respectively. The multi-objective optimization further provides a high-performance and cost-effective design solution for the hybrid system.