Morphology and strain control of hierarchical cobalt oxide nanowire electrocatalysts via solvent effect
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Morphology and strain control of hierarchical cobalt oxide nanowire electrocatalysts via solvent effect Xiuming Bu1,2,§, Xiongyi Liang1,§, Kingsley O. Egbo2, Zebiao Li1, You Meng1, Quan Quan1, Yang Yang Li1, Kin Man Yu2, Chi-Man Lawrence Wu1 (), and Johnny C. Ho1,3 () 1
Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong SAR, China Department of Physics, City University of Hong Kong, Kowloon, Hong Kong, Kowloon, Hong Kong SAR , China 3 State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon, Hong Kong SAR, China § Xiuming Bu and Xiongyi Liang contributed equally to this work. 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 30 April 2020 / Revised: 25 June 2020 / Accepted: 12 July 2020
ABSTRACT Designing highly efficient and low-cost electrocatalysts for oxygen evolution reaction is important for many renewable energy applications. In particular, strain engineering has been demonstrated as a powerful strategy to enhance the electrochemical performance of catalysts; however, the required complex catalyst preparation process restricts the implementation of strain engineering. Herein, we report a simple self-template method to prepare hierarchical porous Co3O4 nanowires (PNWs) with tunable compressive strain via thermal-oxidation-transformation of easily prepared oxalic acid-cobalt nitrate (Co(NO3)2) composite nanowires. Based on the complementary theoretical and experimental studies, the selection of proper solvents in the catalyst preparation is not only vital for the hierarchical structural evolution of Co3O4 but also for regulating their compressive surface strain. Because of the rich surface active sites and optimized electronic Co d band centers, the PNWs exhibit the excellent activity and stability for oxygen evolution reaction, delivering a low overpotential of 319 mV at 10 mA·cm−2 in 1 M KOH with a mass loading 0.553 mg·cm−2, which is even better than the noble metal catalyst of RuO2. This work provides a cost-effective example of porous Co3O4 nanowire preparation as well as a promising method for modification of surface strain for the enhanced electrochemical performance.
KEYWORDS hierarchical structure, morphology control, compressive strain, solvent effect, oxygen evolution reaction
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Introduction
Electrochemical water splitting into hydrogen and oxygen provides an efficient energy conversion technology to reduce the dependence on carbon-based fossil fuels as well as their negative impact on the environment [1, 2]. As compared with the two-electron transfer hydrogen evolution reaction (HER) at cathode, the oxygen evolution reaction (OER) is a four-electron process with the slower kinetics being a limiting factor for the further efficiency improvement of overall water splitting [3]. Thus, it is necessary to develop efficient non-noble metal and earth-abundant OER catalysts to lower the reaction energy barrier. Among many promising catalyst materials, transition m
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