BACKGROUND At present, much attention has been focused on the development of methane (CH4) sensors due to a series of explosions and fires caused by CH4 gas leakage. RESULTS Here, a CH4 thermoelectric gas sensor (TGS) was fabricated by fixing 3D porous palladium/cobalt oxide (Pd/Co3O4) catalyst on a commercial thermoelectric module. 3D porous Pd/Co3O4 catalysts were prepared by a co-precipitation and gel-casting method. The pore structure in catalysts could be tailored only by adjusting the gel viscosity during the formation process. The protocol to tune the pore structure is facile and effective for the improvement of the activity of catalysts. By means of various techniques, the catalysts were characterized and then the possible catalytic mechanism was revealed. The CH4 TGS based on the optimal Pd/Co3O4 catalyst began to respond at 200 degrees C, following an obvious output voltage (Delta V) of 5 mV. Enhancing the operating temperature to 240 degrees C, the value of Delta V reached to 31 mV and exhibited a linear relationship with CH4 gas concentration. Meanwhile, the CH4 TGS showed high sensitivity, repeatability and stability. CONCLUSION The easy and effective preparation method presented to prepare 3D porous Pd/Co3O4 catalyst can provide an unique perspective on the development of 3D porous materials with excellent properties. It can be anticipated that the CH4 TGS based on the 3D porous Pd/Co3O4 catalyst will be a potential candidate for the detection of CH4 gas in industrial settings. (c) 2020 Society of Chemical Industry