Carbon monoxide sensor with reduced hydrogen cross sensitivity

A carbon monoxide sensor with minimal hydrogen cross sensitivity comprising:

• a base comprising a bottom wall and a cylindrical side wall to define an interior space, the base including first and second electrical terminals;
• an electrode stack in the housing interior space comprising concentric circular stack layers including a counter electrode, a sensing electrode and a thin separator layer between the counter electrode and the sensing electrode, the counter electrode comprising a membrane having a layer of platinum black catalyst, and the sensing electrode comprising a membrane having a layer of platinum black catalyst, wherein the counter electrode includes a lower amount of platinum black catalyst than the sensing electrode;
• current collectors electrically connecting the counter and sensing electrodes to the respective first and second electrical terminals whereby sensor current represents concentration of carbon monoxide;
• and
• a top connected to the cylindrical sidewall to close the interior space and including a gas entry hole.