  Black holes are arguably the most extreme regions of the universe. Yet, they
are also utterly inaccessible to experimentation, and even just indirect
observation poses significant technical challenges. The phenomenological
approach of thermodynamics is uniquely suited to explore at least some of the
physical properties of such scenarios, and this has motivated the study of
so-called holographic engines. We show that the efficiency of an endoreversible
Brayton cycle is given by the Curzon-Ahlborn efficiency if the engine is fueled
by a 2-dimensional ideal gas; and that the efficiency is higher, if the working
medium is a (2+1)-dimensional BTZ black hole. These findings may be relevant
not only in the quest to unlock the mysteries of black holes, but also for
potential technological applications of graphene.
