In-situ energy recovery coupled with CO 2 sequestration via CO 2 /CH 4 exchange. Replacing the original methane in natural gas hydrates with CO 2 presents a promising strategy for liberating methane for energy and locking CO 2 for sequestration in a single dual-purpose process (Fig ). This gasswapping phenomenon is well grounded in the thermodynamic basis. CO 2 has a higher affinity toward occupying water cages compared to methane. Therefore, exposing natural gas hydrates to CO 2 gas under appropriate conditions leads to a spontaneous replacement of CH 4 by CO 2 in the water cages without destroying the host lattice. However, exploiting this beneficial phenomenon has not been practical due to the slow CH 4 /CO 2 exchange process. The CH 4 /CO 2 exchange kinetics is feasible only at the hydrate surface and at the beginning when the methane hydrate first contacts the CO 2 gas, but diminishing rapidly once the newly formed shell of CO 2 hydrate covers the original hydrate particle. The subsequent guest-exchange process stops because of the limited gas diffusion in the bulk phase of the hydrate. We postulate that adding dopants to the CO 2 gas can resolve this kinetics issue. The gaseous dopants (methanol, ammonia, etc.) migrate to the hydrate surface and create lattice defects which then diffuse into the hydrate phase through the mechanism in