The re-issues of this story are degrading quickly. They created an extremely large, extremely inefficient, extremely low power capacitor. Its battery equivalent would be about the size of a backpack. It can not be repaired or upgraded without destroying the concrete the carbon black is mixed into. Concrete is also a porous material so if it got wet it would short and potentially kill someone completing a circuit to ground.
In other words, this isn’t useful and doesn’t improve on anything we already have. They simply used a material we already have to create a poor performing capacitor.