Impact of pH and Composition of Phosphovanadomolybdate Anionic Catholytes on the Performance of Redox Flow Polymer Electrolyte Fuel Cells (Supporting Information)

A H15P3V6Mo18O84 aqueous solution containing phosphovanadomolybdate anions such as [PV3Mo9O40]6− and [PV2Mo10O40]5− were applied to a catholyte of redox flow polymer electrolyte fuel cells (PEFCs). This system enables continuous power generation by the electrochemical reduction of the phosphovanadomolybdate anions over the carbon cathode and subsequent reoxidation of the reduced phosphovanadomolybdate anions in the cathode tank. Currently, investigations on H15P3V6Mo18O84 aqueous solution have been limited to compositional analysis only, and there are no reports of its application to the catholyte. In this study, the performance of H15P3V6Mo18O84 aqueous solution using as the catholyte in redox flow PEFCs was investigated. In addition, the pH of catholytes was increased, and effects on the performance were compared. Current–voltage measurements showed that increasing the pH (0.3 → 2.5) decreased the power density (42 mW cm−2 → 17 mW cm−2). On the other hand, the reduction–reoxidation operation showed that increasing the pH increased the reoxidation rate of the phosphovanadomolybdate anions (0.5 mmol min−1 → 2.2 mmol min−1). This study is the first step toward the use of H15P3V6Mo18O84 aqueous solution as a catholyte in redox flow PEFCs.

本实验中，以含磷钒钼酸盐阴离子如[PV3Mo9O40]6−和[PV2Mo10O40]5−的H15P3V6Mo18O84水溶液应用于红ox流聚合物电解质燃料电池（PEFCs）的阴极。该系统通过在碳阴极上对磷钒钼酸盐阴离子的电化学还原以及在阴极罐中对还原的磷钒钼酸盐阴离子的后续氧化，实现了持续的电功率生成。目前，对H15P3V6Mo18O84水溶液的研究仅限于组成分析，尚未有将其应用于阴极的报道。在本研究中，考察了将H15P3V6Mo18O84水溶液用作红ox流PEFCs阴极时的性能。此外，还比较了提高阴极溶液pH值（0.3 → 2.5）对性能的影响。电流-电压测量表明，pH值的增加导致功率密度（42 mW cm−2 → 17 mW cm−2）降低。另一方面，还原-氧化操作表明，pH值的增加提高了磷钒钼酸盐阴离子的氧化速率（0.5 mmol min−1 → 2.2 mmol min−1）。本研究是首次将H15P3V6Mo18O84水溶液作为红ox流PEFCs阴极的初步探索。