Abstract: A device for decomposing the oxides of nitrogen (Nox) contained in effluent compositions, such as the exhaust gases generated by automotive combustion engines, is described. In one embodiment, the device includes a reaction chamber containing an oxidisable material which when the device is in use will undergo an oxidation/reduction reaction with nitrogen oxides of nitrogen oxidation states greater than 2, especially nitrogen dioxide, to generate nitrogen and an oxide of the oxidisable material. The oxidisable material is regenerated using an electromotive force. In a particularly preferred embodiment, the reaction chamber containing the oxidisable material is associated with a further reaction chamber which is arranged upstream of the reaction chamber containing the oxidisable material. This further reaction chamber contains an oxidation catalyst which is able to oxidize nitric oxide (NO) to nitrogen dioxide (NO2) or other nitrogen oxides having a nitrogen oxidation state greater than 2.