An array-type sensor that senses NH3 includes non-Nernstian sensing elements constructed from metal and/or metal-oxide electrodes on an O2 ion conducting substrate. In one example sensor, one electrode may be made of platinum, another electrode may be made of manganese (III) oxide (Mn2O3), and another electrode may be made of tungsten trioxide (WO3). Some sensing elements may further include an electrode made of La0.6Sr0.4Co0.2Fe0.8O3 and another electrode made of LaCr0.95Mg0.05O3.