An oxidation-nitridation-denitridation approach to transform metal solids into foams with adjustable pore sizes for energy applications

Abstract Metal foams with hierarchically porous structures are highly desirable in energy applications as active materials or their host substrates. However, conventional preparation methods usually have a quite limited flexibility of adjusting pore size of metal foams. Herein, an alternative new method based on gaseous thermal oxidation-nitridation-denitridation processes was developed to prepare metal (copper and nickel) foams with adjustable pore size by controlling the thermal nitridation temperature. Moreover, this environment-friendly method is independent of the shape of starting pure metal substrates and can be repeatedly applied to the metal substrates to create hierarchical porous structures containing different size pores. As a demonstration of the advantages of the resultant foams with abundant pores by this method, compared with its starting material (commercial Ni foam with the pore size of several millimeters), the resultant hierarchical porous Ni foam gives the remarkably enhanced performance of electrochemical water splitting as HER/OER electrodes and electrochemical energy storage as the host substrate of capacitive material MnO2. The metal foams with adjustable pore size prepared by the developed method will find a wide range of important applications in energy storage and conversion areas.