We describe a method of storing a gas, in particular hydrogen, comprising: providing a polymer sponge, wherein said polymer sponge comprises a plurality of catalytic nanoparticles; providing a solution of reactants, catalyzed by said nanoparticles to produce said gas; absorbing said solution into said polymer sponge such that said reactants react within said polymer sponge to produce said gas; wherein said gas is held within said polymer sponge; and wherein said polymer sponge comprises a thermally responsive polymer having a volume which reduces with a change in temperature, such that said gas held within said polymer is extractable by changing a temperature of said polymer sponge.