Room temperature NH3 gas sensors based on Pt and Pt-Ir (Ir doping Pt) porous ceramic electrodes have been fabricated by both electroplating and sputtering methods. The properties of the gaseous ammonia sensors have been examined by polarization and chronoamperometry techniques. The influence of humidity on the features of the resulting sensors in the system has also been discussed, and the working potential was optimized. Water vapors seem to hugely improve the electrochemical activity of the electrode. With increasing the relative humidity, the response of the Pt-Ir(E)/Pt(S)/PCP sensor to NH3 gas could be enhanced remarkably, and the sensitivity increases from 1.14 to 12.06 mu A ppm(-1) cm(-2). Then we have also discussed the sensing mechanism of the Pt-Ir sensor and the result has been confirmed by X-ray photoelectron spectroscopy of the electrode surface before and after reaction in the end. (C) 2016 Elsevier B.V. All rights reserved.