Micro-fuel cell sensor apparatus

A sensor for measuring partial hydrogen pressure in a gas stream, comprising:

• a housing;
• a sensing element comprising first and second gas diffusing electrodes spaced from one another and disposed in said housing;
• a fuel-cell spacer having an acidic electrolyte disposed between said first and second electrodes;
• a first gas permeable membrane separating said first electrode from the gas stream and enabling hydrogen diffusion therethrough for contact with said first electrode, said first membrane being spaced from said first electrode by a first cavity enabling hydrogen diffused through said first membrane to contact said first electrode;
• a second gas permeable membrane separating said second electrode from atmospheric air and defining a second cavity therewith isolated from said first cavity;
• a seal precluding contact between hydrogen in the first cavity and the second electrode;
• and
• means for maintaining a hydrogen partial pressure gradient between said first electrode and an external gas stream containing hydrogen.