Optimizing microwave frequencies for hydrogen and electromagnetic shielding materials production through methane pyrolysis over biochar

Clean hydrogen production through methane pyrolysis over renewable biochar offers a promising avenue for sustainable energy generation. Herein, an innovative approach that utilizes variable microwave frequencies to facilitate methane pyrolysis is introduced. The frequency optimization study reveals that a frequency of 4225 MHz maximizes methane conversion, yielding an impressive rate of 90.7 % at 100 W microwave power. However, prolonged pyrolysis under the same frequency for 60 min leads to a diminished conversion, resulting in a reduced efficiency of 43.9 %. Notably, by alternating microwave frequencies to 4400, 5150, 4600, and 4620 MHz, the reactivation of deactivated biochar is achieved, consistently restoring efficiency to over 97 % for five consecutive cycles. The transition from polarization-driven loss to conduction-induced loss is identified as the key mechanism responsible for the in-situ reactivation of spent biochar, which is controlled by varying microwave frequencies. Moreover, the spent biochar exhibits a heightened microwave-absorbing capacity, characterized by an exceptionally low reflection loss of −73.1 dB at a thickness of 2.1 mm. Hence, adjusting microwave frequencies to enhance methane pyrolysis not only promotes clean hydrogen production but also yields high-performance electromagnetic shielding materials. This dual outcome optimizes sustainable methane pyrolysis for efficient hydrogen production.