Development of Nitrogen Doped Carbon Supported PtNi Alloy with a Pt Shell for the Production of Impurity-Free V^3.5+ Electrolyte for Vanadium Redox Flow Batteries

The catalytic reduction method using formic acid as a reducing agent is simple and cost-effective for the preparation of impurity-free V3.5+ electrolyte for vanadium redox flow batteries (VRFBs). However, it requires a highly active and stable catalyst to improve the conversion rate of vanadium ion in a strong acid environment. In this study, the PtNi alloy catalyst supported on N-doped carbon (PtNi/NC) is developed for use in the catalytic reduction method. The strong interaction between the catalyst and N-doped carbon support as well as the PtNi alloying effect in PtNi/NC contributes to the enhanced catalytic activity for both the oxidation of formic acid and the reduction of V4+. As a result, a conversion rate of 2.25 times higher than that of the commonly used Pt/C catalyst was achieved. In addition, since the prepared V3.5+ electrolyte does not contain residual metal ions, side reactions such as hydrogen generation do not occur while operating VRFBs. The VRFB single-cell test successfully demonstrates that PtNi/NC is an effective catalyst to replace conventional Pt/C for the catalytic reduction method.