General Recyclable Redox-Metallothermic Reaction Route to Hierarchically Porous Carbon/Metal Composites

Abstract

Herein, we develop a general synthetic route to obtain composites of porous carbon and electrochemically active metal particles such as Ge, In, Bi, and Sn. The thermolysis of a Zn-based metal-organic framework (MOF) produces hierarchically porous carbon (HPC) and metallic Zn at high temperatures, which can act as a reducing agent of metal oxides. In the reaction system of a Zn-based MOF with GeO2, in situ evolved Zn reduces GeO2, producing Ge and ZnO. Interestingly, ZnO is automatically reduced to Zn via a carbothermic reduction during the conversion process, which returns reducing agent to the reaction. Thus, the repeated occurrence of the zincothermic and carbothermic reduction reactions promotes a recyclable redox-metallothermic reaction. After complete reduction of GeO2, Zn metal is spontaneously vaporized to yield Ge/HPC composites. This facile method can be successfully extended to other metal oxides including In2O3, Bi2O3, and SnO. The as-synthesized Ge/HPC is tested as a rechargeable battery anode material, which exhibits a reversible capacity as high as ∼600 mA h g-1 after 300 cycles at a rate of 0.5 C and a low electrode volume expansion (less than 30%).