Abstract: A composite material for use in a sensing electrode. The composite material comprises a first phase and a second phase. The first phase consists essentially of Bi2Ru2O7+x wherein x is a value between 0 and 1 and the second phase consists essentially of RuO2.

Abstract: A sensor for measuring the oxygen and/or unburnt fuel content of a combustion gas includes an outer tube (20) sealed at one end by a pellet (17) of oxygen sensitive solid electrolyte. Solid electrolyte (17) has an electrode (21) formed on the outer side thereon. The sensor also includes an inner tube (13) that is sealed by a disc (14) of solid electrolyte. Disc (14) has electrodes (15, 16) formed on the inner and outer surfaces thereof. The internal side of solid electrolyte (17) is electrically connected to electrode (16). Outer tube (20) is provided with apertures (24) and the annular space between outer tube (20) and inner tube (13) is coated with a platinum catalyst (18). In use, combustion gas contacts outer electrode (21). Combustion gas passes through apertures (24) and along the annular space. During passage of combustion gas through the annular space, the combustion gas comes into close proximity with the oxidation catalyst (18) and the oxidation catalyst (18) acts to equilibrate the combustion gas.