Leak detection unit for refrigerant system

An HVAC system comprising:

• an air supply system;
• a refrigerant circuit configured to condition air in the air supply system;
• and
• an electrochemical sensor configured to detect a refrigerant leak from the refrigerant circuit;
• wherein the sensor is a solid polymer electrolyte (SPE) electrochemical (EC) sensor, wherein the sensor is configured to sense hydrocarbons or substituted hydrocarbons, the sensor comprising:
• a housing;
• a membrane electrode assembly disposed in the housing, the membrane electrode assembly comprising a sensing electrode comprising a first catalyst comprising noble metal nanoparticles, a counter electrode comprising a second catalyst comprising noble metal nanoparticles, and a solid polymer electrolyte disposed between the sensing electrode and the counter electrode;
• wherein the nanoparticles of the first catalyst are supported on the support, the support comprising an oxidation-resistant conductive support including oxidation-resistant support particles larger than the nanoparticles of the first catalyst.