A kinetic study of Ag electrodes on Na2CO3/BaCO3 solid electrolyte using pressure modulation and electrochemical impedance spectroscopy reveals that the response to CO2/O-2 partial pressure changes is determined by a combination of a reaction process and subsequent diffusion of Ag+ ions into the carbonate. This Ag+ ion doping is assumed to enhance CO2 exchange kinetics at the carbonate/electrode interface and to be responsible for the observed improved CO2 gas-sensing performance.