This work reports the fabrication of concentration-cell-type hydrogen sensors based on a protonated Nafion membrane and their hydrogen sensing characteristics. Platinum on carbon black deposited on porous Nafion substrates is used as a catalytic active electrode. The hydrogen sensors are capable of detecting hydrogen concentrations of 3.9-99.95%. The response time is in the range of 1-15 s, and a stable linear voltage output is observed. These solid-state potentiometric hydrogen sensors show good sensitivity, short response time, wide linear range, and long-term stability greater than 3 months, suggesting their potential application for environmental monitoring.