A solid-state electrochemical sensor for hydrogen determination in air is described. The device incorporates a protonic conductor based on polybenzimidazole doped with phosphoric acid as the electrolyte and a Ag-AgCl, KCl electrode as the reference electrode. Pt grid or Pt supported on carbon are tested as the sensitive electrode. The performance characteristics of both types of sensor including either the Pt grid or the carbon-supported Pt electrode are reported.