PEROVSKITE ELECTROCATALYSTS FORTHE OXYGEN EVOLUTION REACTION

catalyst;oxygen evolution reaction;Chemical & Biomolecular Engineering

Wang, NingWang, Chao ;

Johns Hopkins University

关键词: catalyst;    oxygen evolution reaction;    Chemical & Biomolecular Engineering;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/39243/WANG-THESIS-2014.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

To commercialize clean-energy technologies such as water electrolyzers and fuel cells, highly efficient electrocatalysts are needed to improve the kinetics of the oxygen evolution reaction (OER). Perovskites have recently received substantial interest as they could be more cost-effective than, while possess comparable catalytic activities with, the state-of-the-art IrO2 and RuO2 electrocatalysts for the OER. While the previous studies are mostly reported on thin-film or micrometer-scale catalysts, this work aims to develop advanced perovskite nanocatalysts for the OER. LaMO3 (M=Ni, Co, Fe, Mn) perovskite nanocatalysts (5─300 nm) are synthesized by sol-gel methods, with the morphological and crystalline sizes controlled by tuning the protocols of calcination and/or using silica templates. These materials are characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and X-ray diffraction (XRD). Electrocatalytic performance towards the OER is studied in alkaline solution by using a rotating disk electrode (RDE) and a three-electrode electrochemical cell. It is found that the catalytic performance of different perovskites of similar sizes follows the trend: La2NiO4> LaNiO3>LaCoO3>LaMnO3+δ>LaMnO3>LaFeO3, consistent with previous results obtained on microcrystalline catalysts. The two Ni perovskite catalysts are found to show interesting redox peaks during the OER which could be assigned to Ni2+/Ni3+ conversion. In addition, size-dependent electrocatalytic performance of the perovskite catalysts is revealed by studying LaCoO3 catalysts of different sizes.In general, smaller particles give higher mass activity, except the nanoporous LaCoO3 made with silica template. The later, however, shows smaller Tafel slope than the other catalysts with larger crystalline sizes. This indicates that the intrinsic (surface-specific) catalytic activity and kinetics of the OER improves with decreasing particle size, while the relatively low mass activity of nanoporous LaCoO3 could be due to mass transportation limits within the nanoscale pores. These findings represent important steps toward development of high-surface-area, precious metal-free catalysts for electrical-chemical energy conversion and fundamental understanding of the structure-property relationships of metal oxide nanomaterials in electrochemical reaction environments.