Yea that video is helpful and it looks like mechanical energy or thermal could be used to deform the graphene film to do some work on that film which them stores it. So it seems like what’s happening is that thermal energy is being used to put energy into the free standing graphene lattice. Then as it extends in length due to the film heating, it stores energy almost like inflating a balloon, then it touches one of the electrodes nearby and the electrons in this unique material transfer charge to the other electrode and causes the film to contract so a portion of the charge was transferred away, and it contracts then can repeat the process. So it’s a small motor that harvests either mechanical or thermal energy. But given the tiny size, it would seem like thermal might be the dominant thing since the membrane would probably need some sort of mass to benefit from random movements. Or the graphene would need to be extremely flexible. But not totally sure..