Production of hollow and porous Fe2O3 from industrial mill scale and its potential for large-scale electrochemical energy storage applications

Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe2O3 micro-rods using a facile and scalable chemical treatment. The Fe2O3 morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe2O3 supercapacitor electrode delivered a specific capacitance of 346 F g(-1) at 2 mV s(-1) with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g(-1) at 0.1C, reducing to 933 mA h g(-1) after 100 cycles and to 673 mA h g(-1) at 5C. The Fe2O3 electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe2O3 in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.