One of the alternatives to carbon-based fuels is hydrogen. Hydrogen isotopes are expected to be used as a fuel for nuclear fusion power. The measurement of these isotopes in high-temperature environments (>350 °C) is of great interest. Electrochemical sensors based on solid-state electrolytes have been proved to be able to operate at elevated temperatures, with great physical and chemical stabilities. In the present work, BaCe0.6Zr0.3Y0.1O3-α (BCZY) was used as a proton-conducting solid-state electrolyte. The synthesized powder was shaped into pellets at 1400 °C for 30 h and 1650 °C for 6 h and adding 5 mol% ZnO as sintering aid at mild sintering conditions (1400 °C for 12 h). Electrochemical sensors were constructed and tested using these pellet shaped electrolytes. The sensors were used in a potentiometric configuration at 400 °C, 500 °C and 600 °C. Hydrogen concentrations in the working electrode ranged from 0.02 to 0.5 mbar H2 in Ar. The use of ZnO as sintering aid helped in the obtention of full dense ceramics, preserving the perovskite structure of the electrolyte. Moreover, the addition of ZnO yielded a sensor that practically fulfilled the Nernst equation and able to perform hydrogen measurements with a high accuracy and precision.