Template-Free Routes to Macroporous Monoliths of Nickel and Iron Oxides: Toward Porous Metals and Conformally Coated Pore Walls

In our continuing efforts to prepare macroporous monoliths of functional inorganic materials through novel template-free routes, we present here routes to porous NiO starting from Ni−Zn oxalates, and to porous ZnFe 2 O 4 starting from Zn−Fe oxalates. Monolithic Ni has been prepared from porous NiO by hydrogen reduction, with retention of the macropore structure. Heating porous ZnFe 2 O 4 under high hydrogen flow rates simultaneously reduces the metals and transports zinc in the vapor phase, leaving behind a macroporous Fe monolith. Robust monoliths with pore dimensions ranging from 1 to 5 μm have been formed in all cases, with narrow pore diameter distributions. To further functionalize the porous NiO monolith, we have dip-coated a lanthanum source and fired it in air to obtain a conformal coating of La 4 Ni 3 O 10 particles on the surfaces of the NiO pore walls. Unlike conventional dip-coating, the skeletal support is itself a reactant in this process, ensuring that the coating is well-dispersed on the pore walls.