Transition metal–based composites for oxygen evolution electrocatalysis and lithium ion storage

Abstract

Green energy technologies are urgently needed due to an increasing global energy demand as well as critical environmental and climate concerns associated with the burning of fossil fuels. Electrochemical energy devices allowing direct conversion between chemical energy and electrical energy in an environmentally friendly way are of great interest. Efficient oxygen evolution reaction (OER) electrocatalysts and high-performance anode materials are crucial for rechargeable metal-air batteries and lithium ion batteries (LIBs), respectively. This Ph.D. project aims at using cheap and environment friendly iron compounds for OER electrocatalysts and anode materials of LIBs. The critical role of the crystalline structure, morphology and functional properties of final active iron-based materials is systematically investigated, as summarized below: 1. Ultrafine Fe3O4 nanoparticles (diameter: 6 ± 2 nm) are homogeneously immobilized on 2D Ni based metal-organic frameworks (MOFs) for OER. Electronic structure modulation and morphology changes for optimized catalytic activity are studied via varying the amount of Fe3O4 in the composite (Fe3O4/Ni-BDC). The optimized Fe3O4/Ni-BDC achieves the best OER performance at an overpotential of 295 mV at 10 mA cm-2, a Tafel slope of 47.8 mV dec-1 and considerable catalytic durability (40 h). The effect of valance state of the transition metal upon OER performance in the composites is carefully discussed. In conclusion, the optimized Fe3O4/Ni-BDC shows a promising OER catalytic performance. 2. A flower-like composite consisting of internal Fe2O3 nanocrystals and outer hierarchal iron doped K-birnessite type MnOx layers (Fe2O3@Fe doped K-birnessite) is synthesized by a facile one-pot microwave-assisted heating synthesis (MAHS). The crystallinity and morphology evolution of Fe2O3@Fe doped K-birnessite composite are studied by characterizing the products at various reaction times. Key factors affecting the morphology such as reaction temperature and stoichiometric ratio of precursors are systematically investigated. When tested for LIBs, the optimized hybrid Fe2O3@Fe doped K-birnessite composite exhibits a high reversible capacity of 758 mA h g−1 at 500 mA g−1 after 200 cycles, outperforming the pure K-birnessite (203 mA h g−1). Compared with other related report, the composite (Fe2O3@Fe doped K-birnessite) exhibits a comparable performance for lithium ion storage.