Operando Monitoring of Hydrogen/Vanadium Redox Flow Batteries Using an Embedded Eight-in-One Microsensor

A flexible eight-in-one microsensor was developed using micro-electro-mechanical systems (MEMS) technology for monitoring hydrogen/vanadium redox flow batteries (HVRFBs). The device integrates sensing functions for voltage, current, conductivity, temperature, pressure, humidity, flow rate, and hydrogen. During battery operation, the voltage measurements showed an approximately 200 mV difference between the upstream and downstream regions during charging, indicating spatial variation in the measured voltage. Conductivity, temperature, flow rate, and pressure measurements were also used to monitor operating conditions within the HVRFB. The hydrogen sensor was evaluated at one tested location under the hydrogen exposure condition used in this study; its resistance decreased and approached a steady response. Because measurements at multiple hydrogen concentrations were not conducted, concentration-dependent sensitivity, response and recovery times, and the limit of detection were not established. During a 200 h charge–discharge test at 25 °C, signals from the integrated sensing functions, including the SnO2/Pd hydrogen sensor, remained observable. However, quantitative pre- and post-test calibration data were not available to determine sensitivity retention, signal drift, or passivation. These results demonstrate the feasibility of integrating multiple sensing functions for monitoring HVRFB operation, but further testing is needed to quantify hydrogen-sensing performance and long-term stability.