An electro-galvanic fuel cell is an electrical device, one form of which is commonly used to measure the concentration of oxygen gas in scuba diving and medical equipment. A chemical reaction occurs in the fuel cell when the potassium hydroxide in the cell comes into contact with oxygen. This creates an electric current between the lead anode and the gold-plated cathode through a load resistance. The current produced is proportional to the concentration (partial pressure) of oxygen present. They are used in oxygen analysers in technical diving to display the proportion of oxygen in a nitrox or trimix breathing gas before a dive. They are also used in electronic, closed-circuit rebreathers to monitor the oxygen partial pressure during the dive. The partial pressure of oxygen in diving chambers and surface supplied breathing gas mixtures can also be monitored using these cells. This can either be done by placing the cell directly in the hyperbaric environment, wired through the hull to the monitor, or indirectly, by bleeding off gas from the hyperbaric environment or diver gas supply and analysing at atmospheric pressure, then calculating the partial pressure in the hyperbaric environment. This is frequently required in saturation diving and surface oriented surface supplied mixed gas commercial diving. Electro-galvanic fuel cells have a limited lifetime which is reduced by exposure to high concentrations of oxygen. The reaction between oxygen and lead at the anode consumes lead, which eventually results in the cell failing to sense high concentrations of oxygen. Typically, a cell used for diving applications will function correctly for 3 years if stored in a sealed bag of air but only for four months if stored in pure oxygen.
20th Jan 2015