Electrochemical Oxidation of Methane in Nonaqueous Electrolytes at Room Temperature: Application to Gas Sensors

The electrochemical oxidation of methane at room temperature was studied using several nonaqueous solvents and electrocatalysts. The best sensitivity and reaction stability were obtained with an electrode composed of platinum black mixed with a 35 weight percent Teflon ® dispersion and deposited on a porous Teflon membrane in contact with an electrolyte of 2 M NaClO 4 in γ‐butyrolactone. A working electrode potential of 800 mV vs. Ag / AgCl gave the least current variation with changing relative humidity. However, a potential of 600 mV vs. Ag / AgCl gave the highest signal‐to‐background current ratio. The sensitivity (net current) measured for the electro‐oxidation of methane in γ‐butyrolactone increased significantly with increasing temperature. The reaction has an activation energy of approximately 12 kcal/ mol. An electrochemical methane monitor was constructed exhibiting a sensitivity of 1 μA/% CH 4 and negligible sensitivity to parts‐per‐million levels of CO or NO 2 . However, it gave responses to > 0.3% H 2 , 49 ppm NO , and 50% C 2 H 6 that could be mistaken for methane signals.