The nature of the most abundant components of the Universe, dark energy and dark matter, is still to be uncovered. I will tackle this subject considering a novel cosmological probe: the neutral hydrogen emitted 21cm radiation, observed with the intensity mapping (IM) technique. In the first part of the talk, I will present the 21cm IM, i.e. what kind of signal it is, how we can model it and what its observational status is. I?ll then present competitive and realistic dark energy and dark matter scenarios (modelled with hydrodynamic and NBody simulations) and show how they produce distinctive and detectable effects on the 21cm signal, presenting forecasts for the Square Kilometre Array.