Towards outstanding performance of direct urea fuel cells through optimization of anode catalyst layer and operating conditions

Abstract

Highlights • The cell performances and characteristics of DUFCs were investigated. • Optimization was performed by varying operating conditions and anode parameters. • Cause for the difference in performance was analyzed in relation to MEA properties. • DUFCs with the optimum conditions had outstanding performance. Direct urea fuel cells (DUFCs) are expected to be ideal devices to protect the ecology and generate energy because they convert urea from urea-rich wastewater and/or urine directly into electrical energy and turn “waste” into “power.” This study investigated the operating conditions of direct urea fuel cells (DUFCs) with commercial catalysts to achieve maximum performance and to accumulate knowledge regarding the electrochemical environment of DUFC full-cell membrane electrode assemblies (MEAs). The cell performance was optimized by experimentally varying the operating conditions (activation process, cell temperature, and reactant concentration) and anode parameters (ionomer ratio and catalyst loading mount). The results were evaluated by comparing the open-circuit voltage (OCV) and maximum power density obtained from the polarization curve. Additionally, the features of MEAs in DUFCs were explored from the viewpoint of performance improvement for the anion exchange membrane (AEM), supply of the liquid anode, and thickness of the bulky catalyst layer, which all have a comprehensive effect on cell performance. The best performance was realized when the single-cell was operated under 0.3 M urea in 1.0 M KOH at 50 ℃ using a KOH pretreatment membrane, and the cell exhibited the highest maximum power density of 57.18 mW cm −2 , To the best of our knowledge, the MEA with the optimum conditions introduced showed the best performance among the DUFCs. This suggests that scientific understanding and analysis of the optimal operating conditions have considerable potential for the development of new catalysts and MEA materials.