The vanishing of reduced ℓ 2 -cohomology for amenable groups can be traced to the work of Cheeger & Gromov in [10]. The subject matter here is reduced ℓ p -cohomology for p ∈]1, ∞[, particularly its vanishing. Results for the triviality of ℓ p H 1 (G) are obtained, for example: when p ∈]1, 2] and G is amenable; when p ∈]1, ∞[ and G is Liouville (e.g. of intermediate growth). This is done by answering a question of Pansu in [34, §1.9] for graphs satisfying certain isoperimetric profile. Namely, the triviality of the reduced ℓ p -cohomology is equivalent to the absence of non-constant harmonic functions with gradient in ℓ q (q depends on the profile). In particular, one reduces questions of non-linear analysis (p-harmonic functions) to linear ones (harmonic functions with a very restrictive growth condition).