Solid-state electrochemical cells can be used to sense and reduce NOx from combustion exhaust gases. In the reduction process the products are N2 and O2. For these cells to be effective in fuel-lean combustion exhaust, cathode materials with high selectivity for NO vs. O2 are necessary. Numerous materials were investigated for NO adsorption and reduction selectivity using temperature programmed desorption and reaction (TPD and TPR), respectively, and a summary of that investigation is given.Ceramic cells using these materials were fabricated and used to electrocatalytically reduce NO. An enhanced electrocatalytic three-way activity for NOx reduction was demonstrated that increases the window of operation into fuel-lean conditions. A process that combines selective absorption of NOx with three-way catalytic or electrocatalytic reduction to further increase the window of operation to higher oxygen concentrations was also demonstrated.