Abstract: A solid state electrochemical cell adapted to alter the composition of gas streams passing therethrough comprising: a porous, high surface area electrolyte forming the body of the cell, said electrolyte having darkened electrocatalytic surfaces; a gas communicating passageway through the cell length; a first electronically conductive region and a second electrolytically conductive region, said regions disposed in opposing segments of the cell; a first electrode located in said first conductive region and a second opposing electrode located within said second conductive region, said solid electrolyte having a transference number of less than 1 and greater than 0.50 in a region between the electrodes.