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Manganese as a Superior Dopant for Oxide Nanosheets in Water Oxidation

The efficiency of water splitting is severely limited by the oxygen evolution reaction (OER), due to sluggish kinetics and a substantial overpotential. To overcome this challenge, precious-metal based catalysts, such as IrO2 and RuO2, have been investigated and confirmed to exhibit good OER performance. However, the scarcity and high cost of these materials restrict their large-scale application.


Recently, the group of Derek Ho and collaborators of the City University of Hong Kong have demonstrated a one-step method for the synthesis of Mn doped ultrathin nickel-iron oxide (Mn-Ni-Fe-O) nanosheets, which simultaneously achieves an abundance of oxygen vacancies and high valance Ni3+ catalytic sites (Fig. 1). The Mn dopant exists in the form of mixed-valence Mn cations, which contributes to tailoring the electronic structure of the Ni and Fe sites, leading to outstanding OER catalytic performance.

Figure 1. Schematic of the preparation procedure of Mn-Ni-Fe-O nanosheets.



SEM and TEM images of the Mn-Ni-Fe-O hybrid shows 100 – 300 nm interconnected nanosheet structures, having an ultrathin and veil-like morphology (Fig. 2). AFM images show a nanosheet thickness of approximately 3.2 nm. EDX mapping presents that Ni, Fe, Mn, and O elements are uniformly dispersed throughout the nanosheets.


Figure 2. (a) SEM image, (b, c) TEM images and the inset in (c) is the corresponding SAED patterns, (d) HRTEM image, (e) AFM image and the corresponding thickness curve, (f) STEM image and the corresponding element mapping, and (g) EDX spectrum of the Mn-Ni-Fe-O nanosheets.



XRD, XPS, CV, and EPR are also performed (Fig. 3). From XPS, after Mn doping, the Fe 2p3/2 XPS peak of the Mn-Ni-Fe-O nanosheets shifts to a higher binding energy as compared to that of undoped Ni-Fe-O nanosheets, suggesting that Mn dopant can modulate the charge density of Fe atom sites. Compared to the Ni 2p XPS spectrum of pristine Ni-Fe-O, the Ni 2p XPS spectrum of Mn-Ni-Fe-O nanosheets exhibits an obvious positive shift of 0.3 eV in binding energy, which is attributed to Mn incorporation. From CV curves, the Ni2+ oxidation peaks appear at 1.40 and 1.36 V versus RHE for the undoped and doped samples, respectively, indicating the oxidation of Ni species is enhanced upon Mn doping. Also, the O2 ratio (51.0 %) for the Mn-Ni-Fe-O nanosheets is higher than that of the Ni-Fe-O nanosheets (41.9 %), which indicates that Mn dopants can create an enhanced oxygen vacancies concentration.

Figure 3. Characterization data of the Mn-Ni-Fe-O and Ni-Fe-O: (a) XRD patterns, (b) XPS survey spectra, (c) high-resolution XPS spectra for Mn 2p region for Mn-Ni-Fe-O, (d) XPS for the Fe 2p region, (e) XPS for the Ni 2p region, CV curves (scan rate of 50 mV s-1) of (f) Ni-Fe-O  and (g) Mn-Ni-Fe-O, (h) XPS for the O 1s region, and (i) electron paramagnetic resonance (EPR) spectra of Mn-Ni-Fe-O (2 wt%).



OER electrochemical performance has been investigated in an O2-saturated KOH (1 M) solution. Upon doping of Mn, polarization curves show an OER overpotential of only 225 mV (vs. undoped at 250 mV) (Fig. 4). Remarkably, these two as-prepared ultrathin nanosheets, with or without Mn doping, exhibit faster OER than the commercial RuO2. The Mn doped nanosheets exhibit a turnover frequency (TOF) of 0.063 s−1 at the overpotential of 300 mV, which is 3.5 and 12 times higher than that of the undoped sample and commercial RuO2, respectively. The Tafel slope is 38.2 mV dec-1 (vs. 65.8 mV dec-1 undoped and 72.0 mV dec-1 from RuO2). Electrochemical impedance spectroscopy (EIS) reveals that the Mn dopants can effectively improve the electrical conductivity.

Figure 4. (a) Polarization curves, (b) TOF, and (c) Tafel slope of Mn-Ni-Fe-O, Ni-Fe-O, and RuO2. (d) Nyquist slopes of Ni-Fe-O and Mn-Ni-Fe-O, (e) overpotential at 10 mA cm-2 and Tafel slope of Ni-Fe-O nanosheets with different Mn doping levels, and (f) chronopotentiometry curves of Mn-Ni-Fe-O nanosheets at 30 mA cm-2.



This work demonstrated a facile method in synthesizing ultrathin Mn-Ni-Fe-O nanosheets that achieve highly efficient OER catalytic performance, providing a sound strategy for the design and synthesis of multi-metallic, atomically-thin oxides nanosheets to mitigate the catalytic limitation of OER, thereby rendering the electrolysis of water a practical form of alternative fuel production.


Information on Corresponding Author


Derek Ho

City University of Hong Kong

Derek Ho is currently an associate professor at the Department of Materials Science and Engineering at City University of Hong Kong. He directs the Atoms to Systems Laboratory. He received his B.A.Sc. (first class) and M.A.Sc. in Electrical and Computer Engineering from the University of British Columbia (UBC), Vancouver, Canada, in 2005 and 2007 respectively. At UBC, he focused his study on microelectronics. He received his Ph.D. in Electrical and Computer Engineering from the University of Toronto, Toronto, Canada in 2013, where he worked on sensors incorporating nanomaterials and CMOS electronics for chemical detection and DNA biosensing applications. Professor Ho’s research interest is in the synthesis of electronic nanomaterials and fabrication of advanced devices. His current research focuses on sensing and energy applications, mainly in the form of stretchable and healable electronics.


Article information:

Mn dopant induced high-valence Ni3+ sites and oxygen vacancies for enhanced water oxidation

Yu Zhang, Zhiyuan Zeng and Derek Ho

Mater. Chem. Front., 2020, Advance Article

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Functional conjugated organic molecules – A collection of articles from Frontiers Journals

We are delighted to share with you a collection of articles from Materials Chemistry Frontiers and Organic Chemistry Frontiers to showcase the key findings and breakthroughs in the field of functional conjugated organic molecules, including the synthesis of the conjugated systems, their properties and applications. This collection is free to access till Jun 19th 2020.


Figuration of bowl-shaped π-conjugated molecules: properties and functions
Masaichi Saito, Hiroshi Shinokubo and Hidehiro Sakurai
Mater. Chem. Front., 2018,2, 635-661

Design strategies of n-type conjugated polymers for organic thin-film transistors
Ying Sui, Yunfeng Deng, Tian Du, Yibo Shi and Yanhou Geng
Mater. Chem. Front., 2019,3, 1932-1951

Research articles

Modulation of luminescence chromic behaviors and environment-responsive intensity changes by substituents in bis-o-carborane-substituted conjugated molecules
Hiroki Mori, Kenta Nishino, Keisuke Wada, Yasuhiro Morisaki, Kazuo Tanaka and Yoshiki Chujo
Mater. Chem. Front., 2018,2, 573-579

Enhancement of intra- and inter-molecular π-conjugated effects for a non-fullerene acceptor to achieve high-efficiency organic solar cells with an extended photoresponse range and optimized morphology
Ning Wang, Lingling Zhan, Shuixing Li, Minmin Shi, Tsz-Ki Lau, Xinhui Lu, Rafi Shikler, Chang-Zhi Li and Hongzheng Chen
Mater. Chem. Front., 2018,2, 2006-2012

One-step rapid synthesis of π-conjugated large oligomers via C–H activation coupling
Shi-Yong Liu, Di-Gang Wang, Ai-Guo Zhong and He-Rui Wen
Org. Chem. Front., 2018,5, 653-661

Folate-conjugated and pH-triggered doxorubicin and paclitaxel co-delivery micellar system for targeted anticancer drug delivery
Lijing Niu, Feiyan Zhu, Bowen Li, Lingling Zhao, Hongze Liang, Yinghua Yan and Hui Tan
Mater. Chem. Front., 2018,2, 1529-1538

Influence of catalytic systems in Stille polymerization on the electrochromic performance of diketopyrrolopyrrole-based conjugated polymers
Wei Teng Neo, Qun Ye, Zugui Shi, Soo-Jin Chua and Jianwei Xu
Mater. Chem. Front., 2018,2, 331-337

Highly efficient transformation of linear poly(phenylene ethynylene)s into zigzag-shaped π-conjugated microporous polymers through boron-mediated alkyne benzannulation
Yoshiaki Shoji, Minsu Hwang, Haruka Sugiyama, Fumitaka Ishiwari, Kumiko Takenouchi, Ryota Osuga, Junko N. Kondo, Shigenori Fujikawa and Takanori Fukushima
Mater. Chem. Front., 2018,2, 807-814

Conjugated molecular dyads with diketopyrrolopyrrole-based conjugated backbones for single-component organic solar cells
Dongdong Xia, Fan Yang, Junyu Li, Cheng Li and Weiwei Li
Mater. Chem. Front., 2019,3, 1565-1573

Preparation of bright-emissive hybrid materials based on light-harvesting POSS having radially integrated luminophores and commercial π-conjugated polymers
Masayuki Gon, Keita Sato, Keigo Kato, Kazuo Tanaka and Yoshiki Chujo
Mater. Chem. Front., 2019,3, 314-320

Fused donor–acceptor π-conjugated diazatruxenones: synthesis and electronic properties
Angela Benito-Hernández, Mardia T. El-Sayed, Juan T. López Navarrete, M. Carmen Ruiz Delgado and Berta Gómez-Lor
Org. Chem. Front., 2018,5, 1748-1755

Orthogonally arranged tripyrrin–BODIPY conjugates with an “edge to plane” mode
Chun-Liang Hou, Yuhang Yao, Da Wang, Jing Zhang and Jun-Long Zhang
Org. Chem. Front., 2019,6, 2266-2274

Near-infrared light-induced shape memory, self-healable and anti-bacterial elastomers prepared by incorporation of a diketopyrrolopyrrole-based conjugated polymer
Yaling Zhang, Shiwei Zhou, Kok Chan Chong, Shaowei Wang and Bin Liu
Mater. Chem. Front., 2019,3, 836-841

Increased conjugated backbone twisting to improve carbonylated-functionalized polymer photovoltaic performance
Tao Zhang, Cunbin An, Kangqiao Ma, Kaihu Xian, Changguo Xue, Shaoqing Zhang, Bowei Xu and Jianhui Hou
Org. Chem. Front., 2020,7, 261-266

Pyridine-terminated low gap π-conjugated oligomers: design, synthesis, and photophysical response to protonation and metalation
Asmerom O. Weldeab, Lei Li, Seda Cekli, Khalil A. Abboud, Kirk S. Schanze and Ronald K. Castellano
Org. Chem. Front., 2018,5, 3170-3177

Molecular modulation of fluorene-dibenzothiophene-S,S-dioxide-based conjugated polymers for enhanced photoelectrochemical water oxidation under visible light
Chunhui Dai, Xuezhong Gong, Xianglin Zhu, Can Xue and Bin Liu
Mater. Chem. Front., 2018,2, 2021-2025

Helicene-derived aggregation-induced emission conjugates with highly tunable circularly polarized luminescence
Chengshuo Shen, Fuwei Gan, Guoli Zhang, Yongle Ding, Jinghao Wang, Ruibin Wang, Jeanne Crassous and Huibin Qiu
Mater. Chem. Front., 2020,4, 837-844

Electrochemical doping engineering tuning of the thermoelectric performance of a π-conjugated free-standing poly(thiophene-furan) thin-film
Wenqian Yao, Lanlan Shen, Peipei Liu, Congcong Liu, Jingkun Xu, Qinglin Jiang, Guoqiang Liu, Guangming Nie and Fengxing Jiang
Mater. Chem. Front., 2020,4, 597-604

Conjugated oligomers with alternating heterocycles from a single monomer: synthesis and demonstration of electroluminescence
Sara Urrego-Riveros, Matthias Bremer, Jonas Hoffmann, Anne Heitmann, Thibault Reynaldo, Janek Buhl, Paul J. Gates, Frank D. Sönnichsen, Muriel Hissler, Martina Gerken and Anne Staubitz
Org. Chem. Front., 2019,6, 3636-3643

The synthesis and properties of a new class of π-expanded diketopyrrolopyrrole analogs and conjugated polymers
Yazhou Wang, Yuchun Xu, Mahesh Kumar Ravva, Yaping Yu, Mingfei Xiao, Xiang Xue, Xinru Yang, Yongming Chen, Zhengke Li and Wan Yue
Org. Chem. Front., 2019,6, 2974-2980

Wave-packet multi-scale simulations based on a non-linear tight-binding Hamiltonian for carrier transport in π-conjugated polymers
Tomofumi Tada
Mater. Chem. Front., 2018,2, 1351-1359

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