Design of a Solid-State Electrochemical Methane Sensor Based on Laser-Induced Graphene for Deployment in the Natural Gas Distribution Network

Methane is a potent greenhouse gas with significant, yet largely unknown, emissions occurring across gas distribution networks and mining/extraction infrastructure. The development of low-cost, low-power electrochemical sensors could provide an inexpensive means to carry out distributed and easy sensing over the entire network and to identify leaks for rapid mitigation. In this work, a simple and cost-effective approach is proposed for developing electrochemical methane sensors which operate at room temperature with the highest reported sensitivity and response time. Laser-induced graphene (LIG) technology, which selectively carbonizes commercial polyimide films using a low-cost CO$_2$ laser cutting and patterning system is utilized. Interdigitated LIG electrodes are infiltrated with a dilute palladium (Pd) nanoparticle dispersion which distributes within and coats the high surface area LIG electrode. A pseudo-solid state electrolyte ionic liquid (IL)/polyvinylidene fluoride was painted onto the flexible cell resulting in a porous electrolyte structure which allows for rapid gas transport and improved three-phase contact between methane, IL and Pd. By subjecting the resulting sensors to methane in a gas flow cell, with off-gas analysis analyzed by Fourier transform infrared spectroscopy, the performance of the sensor over a wide range of operating conditions can be determined and the methane oxidation mechanism can be investigated. The optimized system provides a rapid response (less than 50 s) and high sensitivity (0.55 μA/ppm/cm²) enabling a ppb-level detection limit.