Catalysts All Around Us

Carbon Monoxide Detectors

Increasing awareness of the dangers of carbon monoxide in homes has led to the development of sensors to detect the poisonous gas. Carbon monoxide can accumulate gradually from poorly maintained heaters due to incomplete combustion of fuels.

2CH4 + 3O2

2CO + 4H2O

Detecting CO

The most modern carbon monoxide detectors are battery powered electrochemical devices. Porous platinum electrodes catalyse electrode reactions of carbon monoxide and oxygen as the gases diffuse into the sensor.


CO + H2O

CO2 + 2H+ + 4e






O2 + 4H+ + 4e






The carbon monoxide sensor is based on an electrochemical cell. The electrolytic solution is held in a semi permeable container with a polymer membrane exposed to the air.

Carbon monoxide molecules can pass through this membrane and react at the anode. This frees electrons which are pushed around the circuit to the cathode.

The current flowing between the anode and the cathode is proportional to the concentration of carbon monoxide in the air and is set to trigger an alarm when it reaches a set value. In some parts of the USA all new houses are required by law to install a carbon monoxide detector.

A carbon monoxide detector attached to a wall near a boiler. It's about the size of a smoke alarm.
Carbon monoxide detcotr circuit