The catalytic NO reduction by methane was studied using a (NO,CH4,Ar),Pt vertical bar polybenzimidazole(PBI)-H3PO4 vertical bar Pt,(H-2,Ar) fuel cell at 135 and 165 degrees C. It has been found that, without any reducing agent (like CH4), NO can be electrochemically reduced in the (NO, Ar), Pt/C vertical bar PBI-H3PO4 vertical bar Pt/C, (H-2,Ar) fuel cell with participation of H+ or electrochemically produced hydrogen. When added, methane partially suppresses the electrochemical reduction of NO. Methane outlet concentration monitoring has shown the CH4 participation in the chemical catalytic reduction, i.e., methane co-adsorption with NO inhibited the electrochemical NO reduction and introduced a dominant chemical path of the NO reduction. The products of the NO reduction with methane were N-2, C2H4, and water. The catalytic NO reduction by methane was promoted when the catalyst was negatively polarized (-0.2 V). Repeated negative polarization of the catalyst increased the NO conversion. Maximum NO conversion was 48%. This effect was explained as a result of the reaction of the electrochemically produced hydrogen. (c) 2007 The Electrochemical Society.