Abstract: A sensor for gas species in water includes two membranes separating first, second and third chambers. The first and second chambers are separated by an ion exchange membrane, and the second and third chambers are separated by a gas permeable membrane. Water electrolysis in the first and second chambers provides analyte-ions corresponding to an analyte being detected that pass through the ion exchange membrane from the first chamber to the second chamber. Within the second chamber, these analyte-ions generate analyte via the electrolysis. Analyte in the second chamber passes through the gas permeable membrane to arrive at the third chamber. Within the third chamber, the analyte-ion is generated chemically from the analyte. Electrical detection of the analyte-ion in the third chamber provides sensing of the analyte present in the first chamber.