The design strategy of integrated oxygen microalloying high-entropy alloy (O-HEA) electrode. a) Atomic-level design and the preparation process of O-HEA electrode. Co3O4 powders are selected as micro-alloying ingredients. b) Multilevel structure of O-HEA integrated electrode. The inset is the size of bulk O-HEA electrode. Enlarged views are the molecular structure of black island-like particles Cr2O3 and HEA matrix, respectively. c) O-HEAs integrated electrodes electrochemical application.
(Advanced Materials Doi:10.1002/adma.202101845)
Background
High-entropy alloys (HEAs) are a new type of alloy material with multi-principal solid solution structure. Their unique properties such as high entropy configuration, atomic chemical disorder and lattice distortion endow them potential as good electrocatalysts. Currently reported oxygen evolution reaction (OER) catalysts of HEAs are mainly employed dealloying or magnetron sputtering coating and nanosizing methods to change their structural morphology, increase their specific surface area and exposure more active sites, thus improving their OER catalytic performance. However, conventional HEAs have been rarely studied extensively due to their small specific surface area and low intrinsic activity. The development of a series of modulation tools (microalloying) to optimize the electrocatalytic performance of bulk HEAs is expected to lead to a new type of highly efficient integrated electrocatalytic system, but it is still a great challenge to achieve integrated electrodes from the atomic level design to multilevel structural engineering in simple ways and low prices.
What we discover?
This study cleverly used oxygen microalloying modulation to dope the HEA with Co3O4 oxide with low melting point and good catalytic performance in order to explore the catalytic performance of OER in forming integrated electrodes. Interestingly, the added Co3O4 oxides in the final formed cast HEA electrode turned into Cr2O3 oxide microdomains with island-like structure. Through electrochemical testing of the (Cr, Mn, Fe, Co, Ni, Cu) transition metal-based HEAs electrodes with 35 oxide microdomains of different oxygen contents in seven systems, it was found that the bulk HEA (CrFeCoNi)97O3 exhibited an ultra-low overpotential of 196 mV with ultra-low Tafel slope of 29 mV dec-1 and up to more than 120 h stability in 1 M KOH solution at a current density of 10 mA cm-2. It is shown that the enhanced catalytic performance of the bulk HEA OER is mainly attributed to three points; 1) the formation of Cr2O3 microdomains with island-like structure changes the local coordination environment of the substrate; 2) the leaching of Cr3+ ions promotes the charge transport in the electrolyte; and 3) the amorphization at the interface of the oxide microdomains promotes the formation of active centers.
Why is this important?
Most nanocatalysts with the assistance of current collector manifest preeminent OER performance, yet their insufficient conductivity hinders practical applications. In contrast, the bulk metal material possesses good conductivity but the limited specific surface area constrains its activity enhancement. Therefore, developing an integrated OER electrode with high activity and high conductivity for practical application is highly desirable but remain a challenge. Bulk HEAs that consist of four or more principal elements could act as large-area and highly integrated electrodes in real-life electrolyzers without obvious interfacial resistances, and could combine macroscopic bulk conductivity with dense active sites on the surface, which is beneficial for improving the dilemma confronted by the current mainstream OER electrode composed of current collector and nanocatalyst.
Who did the research?
Zheng-Jie Chen, Tao Zhang, Xiao-Yu Gao, Yong-Jiang Huang, Xiao-Hui Qin, Yi-Fan Wang, KaiZhao,Xu Peng,* Cheng Zhang, Lin Liu, Ming-Hua Zeng,* and Hai-Bin Yu*
1)Z. J. Chen, T. Zhang, X. H. Qin, Prof. Dr. H. B. Yu. Wuhan National High Magnetic Field Center & School of Physic, Huazhong University of Science and Technology, Wuhan 430074, China. Email:haibinyu@hust.edu.cn(H. -B. Y.).
2)Dr. C. Zhang, Prof. Dr. L. Liu. School of Materials science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
3)Y. F. Wang, K. Zhao, Dr. X. Peng, Prof. Dr. M. H. Zeng. College of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062, China. Email:pengxu@hubu.edu.cn(X. P.); Email:zmh@mailbox.gxnu.edu.cn(M.-H. Z.).
4)X. Y. Gao, Prof. Dr. Y. J. Huang. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China.
Adv. Mater. 2021, 2101845 https://onlinelibrary.wiley.com/doi/10.1002/adma.202101845
