Honeycomb β-Ni(OH)2 films grown on 3D nickel foam substrates at low temperature

► Porous, honeycomb β-Ni(OH)2 thick films were grown on 3D nickel foam substrates. ► The honeycomb network is built from seamlessly connected nanowalls, 10-20 nm thick. ► Air annealing of the as-prepared β-Ni(OH)2 films resulted in NiO films. ► The morphologies of the NiO films were similar to those of hydroxide films.