43 results on '"Yonghua Du"'
Search Results
2. Swinging Hydrogen Evolution to Nitrate Reduction Activity in Molybdenum Carbide by Ruthenium Doping
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Ouwen Peng, Qikun Hu, Xin Zhou, Rongrong Zhang, Yonghua Du, Minzhang Li, Lu Ma, Shibo Xi, Wei Fu, Zong-Xiang Xu, Chun Cheng, Zhongxin Chen, and Kian Ping Loh
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General Chemistry ,Catalysis - Published
- 2022
3. Unveiling the Mechanical and Electrochemical Evolution of Nano Silicon Composite Anodes in Sulfide based All-solid-state Batteries
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Daxian Cao, Tongtai Ji, Avtar Singh, Seongmin Bak, Yonghua Du, Xianghui Xiao, Hongyi Xu, Juner Zhu, and Hongli Zhu
- Abstract
The utilization of silicon (Si) anodes in all-solid-state lithium batteries (ASLBs) provides the potential for high energy density. However, the compatibility of sulfide solid-state electrolytes (SEs) with Si and carbon is often questioned due to potential decomposition. To investigate this, operando X-ray absorption near-edge structure (XANES) spectroscopy, ex-situ scanning electron microscopy (SEM) and ex-situ X-ray nano-tomography (XnT) were utilized to study the chemistry and structure evolution of nano Si composite anodes. Results from XANES demonstrated a partial decomposition of SEs during the first lithiation stage, which was further accelerated by the presence of carbon. But the performance of first three cycles in Si-SE-C was stable, which proved the generated media is ionically conductive. XnT and SEM results showed that the addition of SEs and carbon improved the structural stability of the anode with fewer pores and voids. A chemo-elasto-plastic model revealed that SEs and carbon buffered the volume expansion of Si, thus enhancing mechanical stability. The balance between the pros and cons of SEs and carbon in enhancing reaction kinetics and structural stability enabled the Si composite anode to demonstrate the highest Si utilization with higher specific capacities and better rate than pure Si and Si composite anodes with only SEs.
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- 2023
4. Hybrid MoS2+x Nanosheet/Nanocarbon Heterostructures for Lithium-Ion Batteries
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Diana M. Lutz, Mikaela R. Dunkin, Steven T. King, Chavis A. Stackhouse, Jason Kuang, Yonghua Du, Seong-Min Bak, David C. Bock, Xiao Tong, Lu Ma, Steven N. Ehrlich, Esther S. Takeuchi, Kenneth J. Takeuchi, Amy C. Marschilok, and Lei Wang
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General Materials Science - Published
- 2022
5. Investigation of Ca Insertion into α-MoO3 Nanoparticles for High Capacity Ca-Ion Cathodes
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Sanghyeon Kim, Liang Yin, Seong-Min Bak, Timothy T. Fister, Haesun Park, Prakash Parajuli, Jihyeon Gim, Zhenzhen Yang, Robert F. Klie, Peter Zapol, Yonghua Du, Saul H. Lapidus, and John T. Vaughey
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Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Published
- 2022
6. Promoting the Oxygen Evolution Activity of Perovskite Nickelates through Phase Engineering
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Yonghua Du, Qingquan Kong, Fazal Raziq, Jingxuan He, Xingyu Ding, Xiaoqiang Wu, Haiyan Xiao, Shibo Xi, Kelvin H. L. Zhang, Xuguang An, Yang Zhao, Pei Chen, Kaifeng Chen, Chen Huang, Liang Qiao, Yong Wang, and Xiaotao Zu
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Crystal ,Materials science ,Doping ,Oxygen evolution ,General Materials Science ,Crystal structure ,Glassy carbon ,Electrocatalyst ,Engineering physics ,Amorphous solid ,Perovskite (structure) - Abstract
Perovskite oxides have emerged as promising candidates for the oxygen evolution reaction (OER) electrocatalyst due to their flexible lattice structure, tunable electronic structure, superior stability, and cost-effectiveness. Recent research studies have mostly focused on the traditional methods to tune the OER performance, such as cation/anion doping, A-/B-site ordering, epitaxial strain, oxygen vacancy, and so forth, leading to reasonable yet still limited activity enhancement. Here, we report a novel strategy for promoting the OER activity for perovskite LaNiO3 by crystal phase engineering, which is realized by breaking long-range chemical bonding through amorphization. We provide the first and direct evidence that perovskite oxides with an amorphous structure can induce the self-adaptive process, which helps enhance the OER performance. This is evidenced by the fact that an amorphous LaNiO3 film on glassy carbon shows a 9-fold increase in the current density compared to that of an epitaxial LaNiO3 single crystalline film. The obtained current density of 1038 μΑ cm-2 (@ 1.6 vs RHE) is the largest value among the literature reported values. Our work thus offers a new protocol to boost the OER performance for perovskite oxides for future clean energy applications.
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- 2021
7. Understanding the Roles of the Electrode/Electrolyte Interface for Enabling Stable Li∥Sulfurized Polyacrylonitrile Batteries
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Zhaohui Wu, Zulipiya Shadike, Enyuan Hu, Yonghua Du, Haodong Liu, Xiao-Qing Yang, Sicen Yu, Seong-Min Bak, Ping Liu, and Xing Xing
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X-ray absorption spectroscopy ,Materials science ,Scanning electron microscope ,Polyacrylonitrile ,Electrolyte ,Cathode ,Anode ,law.invention ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Chemical engineering ,law ,Electrode ,General Materials Science - Abstract
Sulfurized polyacrylonitrile (SPAN) is a promising high-capacity cathode material. In this work, we use spatially resolved X-ray absorption spectroscopy combined with X-ray fluorescence (XRF) microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy to examine the structural transformation of SPAN and the critical role of a robust cathode-electrolyte interface (CEI) on the electrode. LiSx species forms during the cycling of SPAN. However, in carbonate-based electrolytes and ether-based electrolytes with LiNO3 additives, these species are well protected by the CEI and do not dissolve into the electrolytes. In contrast, in an ether-based electrolyte without the LiNO3 additive, LiSx species dissolve into the electrolyte, resulting in the shuttle effect and capacity loss. Examination of the Li anode by XRF and SEM reveals dense spherical Li morphology in ether-based electrolytes, but sulfur is present in the absence of the LiNO3 additive. In contrast, porous dendritic Li is found in the carbonate electrolyte. These analyses established that an ether-based electrolyte with LiNO3 is a superior choice that enables stable cycling of both electrodes. Based on these insights, we successfully demonstrate the stable cycling of high areal loading SPAN cathode (>6.5 mA h cm-2) with lean electrolyte amounts, showing promising Li∥SPAN cell performance under practical conditions.
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- 2021
8. Understanding Mechanisms of All-solid-state Lithium-Sulfur Batteries through Operando Raman and Ex-situ XAS Studying
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Xiao Sun, Daxian Cao, Seong-Min Bak, Tongtai Ji, Yonghua Du, Michael Geiwitz, Kenneth Burch, and Hongli Zhu
- Abstract
All-solid-state lithium-sulfur batteries (ASLSBs) have been considered a promising next-generation energy storage technology due to their remarkable safety and high energy density. In ASLSBs, the electrochemical pathways are intrinsically different from conventional Li-S batteries using liquid electrolytes. However, the mechanism still lacks clear identification and deep understanding. Herein, for the first time, we investigated the chemistries and explored the electrochemical reaction mechanism and kinetic in ASLSBs through coupling operando Raman spectroscopy and ex-situ X-ray absorption spectroscopy. We proved no long-chain lithium polysulfides (Li2Sn, 4≤n≤8) were formed during the redox reactions, but a short-chain polysulfide (Li2S2) intermediate phase formation was identified in the conversion between active material S8 and reduction product Li2S. The existence of intermediate phase Li2S2 results in low sulfur utilization and poor battery performance. In comparison to liquid cells, ASLSBs exhibit sluggish reaction kinetics due to the higher conversion barrier and slower charger transfer in solid-solid reactions. This study revealed the generation of Li2S2 intermediates in ASLSBs, inspiring future research to further improve the performance of ASLSBs through completing the conversions and promoting reaction kinetics in ASLSBs.
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- 2022
9. Coordinatively and Spatially Coconfining High-Loading Atomic Sb in Sulfur-Rich 2D Carbon Matrix for Fast K+ Diffusion and Storage
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Shimou Chen, Chuankun Jia, Yitai Qian, Yong Qian, Lu Ma, Song Jiang, Yonghua Du, Jie Tian, Ning Lin, and Zheng Yi
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Materials science ,chemistry ,Chemical engineering ,General Chemical Engineering ,Biomedical Engineering ,chemistry.chemical_element ,High loading ,General Materials Science ,Carbon matrix ,Diffusion (business) ,Sulfur - Published
- 2021
10. Highly Selective Acetylene Semihydrogenation Catalyst with an Operation Window Exceeding 150 °C
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Baohui Lou, Weixin Huang, Jie Fan, Shihui Zou, Lu Ma, Wentao Yuan, Yong Wang, Zheng Jiang, Yonghua Du, and Hongquan Kang
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Ethylene ,Materials science ,010405 organic chemistry ,Window (computing) ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Heterogeneous catalysis ,Photochemistry ,Highly selective ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Bismuth ,chemistry.chemical_compound ,Acetylene ,chemistry ,Palladium - Abstract
The operating window (OW) is a primary performance criterion for the selective hydrogenation of acetylene in excess ethylene. Currently, most state-of-the-art catalyst systems have an OW of less th...
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- 2021
11. Mesoporous 3D/2D NiCoP/g-C3N4 Heterostructure with Dual Co–N and Ni–N Bonding States for Boosting Photocatalytic H2 Production Activity and Stability
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Chunmei Li, Shuhao Wang, Hongjun Dong, Shibo Xi, Yun Wang, Huihui Wu, and Yonghua Du
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Boosting (machine learning) ,Materials science ,Renewable Energy, Sustainability and the Environment ,General Chemical Engineering ,Heterojunction ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Nanoclusters ,Chemical engineering ,Photocatalysis ,Environmental Chemistry ,0210 nano-technology ,Mesoporous material - Abstract
The mesoporous 3D/2D NiCoP/g-C3N4 heterostructure is fabricated by embedding NiCoP nanoclusters on the surfaces of g-C3N4 nanosheets, which exhibit more outstanding photocatalytic H2 production act...
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- 2020
12. Rational Design and Synthesis of Hierarchical Porous Mn–N–C Nanoparticles with Atomically Dispersed MnNx Moieties for Highly Efficient Oxygen Reduction Reaction
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Dandan Lyu, Zhi Qun Tian, Xue Xiang, Pei Kang Shen, Xiaoran Zhang, Yonghua Du, Yunqiu Wang, Shibo Xi, Pinsong Chen, and Shuangbao Wang
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Materials science ,Renewable Energy, Sustainability and the Environment ,General Chemical Engineering ,Rational design ,Nanoparticle ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensation reaction ,01 natural sciences ,0104 chemical sciences ,Transition metal ,Chemical engineering ,Environmental Chemistry ,Fuel cells ,Oxygen reduction reaction ,0210 nano-technology ,Hierarchical porous ,Power density - Abstract
Developing transition metal excluding iron and cobalt–nitrogen–carbon (M-N-C) electrocatalysts for oxygen reduction reaction (ORR) is of great practical significance to promote the development of p...
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- 2020
13. Enhanced Electrocatalytic Hydrogen Evolution Activity in Single-Atom Pt-Decorated VS2 Nanosheets
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Lejuan Cai, Xinmao Yin, Lin-Fei Zhang, Yonghua Du, Shibo Xi, Yuxuan Ke, Haibin Ma, Jingting Zhu, Wenjing Zhang, Yang Chai, Andrew T. S. Wee, and Zhuo Wang
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Vanadium disulfide ,General Engineering ,General Physics and Astronomy ,chemistry.chemical_element ,Atom (order theory) ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,chemistry ,General Materials Science ,Hydrogen evolution ,0210 nano-technology ,Platinum - Abstract
Enhancing catalytic activity by decorating noble metals in catalysts provides an opportunity for promoting the electrocatalytic hydrogen evolution reaction (HER) application. However, there are few...
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- 2020
14. Engineering Local and Global Structures of Single Co Atoms for a Superior Oxygen Reduction Reaction
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Wei Liu, Stephen J. Pennycook, Pin Lyu, Chuanhao Yao, Haomin Xu, Zhongxin Chen, Huan Yan, Jia Zhang, Jiong Lu, Chun Zhang, Chenliang Su, Cheng Chen, Xing Li, Xiao Hai, Zejun Li, Jing Li, Xiaoxu Zhao, Shibo Xi, Na Guo, Ming Lin, and Yonghua Du
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Active center ,Materials science ,010405 organic chemistry ,Oxygen reduction reaction ,General Chemistry ,010402 general chemistry ,Photochemistry ,Electrocatalyst ,01 natural sciences ,Catalysis ,0104 chemical sciences - Abstract
The ability to tune both local and global environments of a single-metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs...
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- 2020
15. Probing the Oxidation/Reduction Dynamics of Fresh and P-, Na-, and K-Contaminated Pt/Pd/Al2O3 Diesel Oxidation Catalysts by STEM, TPR, and in Situ XANES
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Yonghua Du, Susanna L. Bergman, Steven L. Bernasek, Lars J. Pettersson, Liene Kienkas, Yu Tang, Jonas Granestrand, Chunhua Tang, and Shibo Xi
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In situ ,Chemistry ,Inorganic chemistry ,technology, industry, and agriculture ,Oxidation reduction ,02 engineering and technology ,respiratory system ,Contamination ,010402 general chemistry ,021001 nanoscience & nanotechnology ,complex mixtures ,01 natural sciences ,Redox ,XANES ,respiratory tract diseases ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,Diesel fuel ,General Energy ,Physical and Theoretical Chemistry ,0210 nano-technology ,human activities - Abstract
This study examines the oxidation and reduction behavior of Pt/Pd/Al2O3 diesel oxidation catalysts at temperatures and gas compositions that model the conditions of the working diesel oxidation cat...
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- 2020
16. Redox Targeting-Based Vanadium Redox-Flow Battery
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Zhenxing Feng, Yuanhang Cheng, Qing Wang, Hang Zhang, Stefan Adams, Widitha Samarakoon, Shibo Xi, Yonghua Du, Feifei Zhang, Songpeng Huang, Xun Wang, and Ya Ji
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Battery (electricity) ,Materials science ,Renewable Energy, Sustainability and the Environment ,business.industry ,Energy Engineering and Power Technology ,Vanadium ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Flow battery ,Redox ,0104 chemical sciences ,Fuel Technology ,Low energy ,chemistry ,Operating temperature ,Chemistry (miscellaneous) ,Materials Chemistry ,Optoelectronics ,0210 nano-technology ,business - Abstract
The low energy density and narrow operating temperature window besides the relatively high cost of the vanadium redox-flow battery (VRB) severely hinder its commercial deployment. Herein, in conjun...
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- 2019
17. Confinement-Induced Giant Spin–Orbit-Coupled Magnetic Moment of Co Nanoclusters in TiO2 Films
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Valeria Lauter, Xiang Ding, Wai Tung Lee, Xiaojiang Yu, Li Ting Tseng, Nina Bao, Sohail Ahmed, Zunming Lu, Jiabao Yi, Chi Xiao, Ajayan Vinu, Xiangyuan Cui, Xinwei Guan, Jun Ding, Yonghua Du, Tao Wu, Kiyonori Suzuki, Andrivo Rusydi, Tao Liu, Rongkun Zheng, Simon P. Ringer, and Xi Luo
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010302 applied physics ,Potential well ,Materials science ,Fabrication ,Magnetic moment ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Nanoclusters ,Magnetization ,Ferromagnetism ,0103 physical sciences ,General Materials Science ,Orbit (control theory) ,0210 nano-technology ,Spin (physics) - Abstract
High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attribute...
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- 2019
18. Copper Single Atoms Anchored in Porous Nitrogen-Doped Carbon as Efficient pH-Universal Catalysts for the Nitrogen Reduction Reaction
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Stephen J. Pennycook, Shibo Xi, Zongkui Kou, Wenjie Zang, Ximeng Liu, Yonghua Du, Yuan Ping Feng, John Wang, Tong Yang, Hong Zhang, Lei Shen, Lele Duan, and Haiyuan Zou
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010405 organic chemistry ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Electrocatalyst ,01 natural sciences ,Redox ,Copper ,Nitrogen ,Catalysis ,0104 chemical sciences ,Ammonia production ,Nitrogen fixation ,Carbon - Abstract
Artificial nitrogen fixation through the nitrogen reduction reaction (NRR) under ambient conditions is a potentially promising alternative to the traditional energy-intensive Haber–Bosch process. F...
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- 2019
19. Electronic and Geometric Structures of Rechargeable Lithium Manganese Sulfate Li2Mn(SO4)2 Cathode
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Shibo Xi, Zhili Dong, Gopinathan Sankar, Tom Baikie, Aravind Muthiah, Minh Phuong Do, Yonghua Du, Timothy I. Hyde, Disha Gupta, Mark Copley, and Madhavi Srinivasan
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Materials science ,Absorption spectroscopy ,General Chemical Engineering ,Analytical chemistry ,chemistry.chemical_element ,General Chemistry ,Manganese ,Electrochemistry ,Cathode ,law.invention ,lcsh:Chemistry ,lcsh:QD1-999 ,chemistry ,X-ray photoelectron spectroscopy ,law ,Oxidation state ,Electrode ,QD ,Lithium ,TJ - Abstract
Here, we report the use of Li2Mn(SO4)2 as a potential energy storage material and describe its route of synthesis and structural characterization over one electrochemical cycle. Li2Mn(SO4)2 is synthesized by ball milling of MnSO4·H2O and Li2SO4·H2O and characterized using a suite of techniques, in particular, ex situ X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy on the Mn and S K-edges to investigate the electronic and local geometry around the absorbing atoms. The prepared Li2Mn(SO4)2 electrodes undergo electrochemical cycles to different potential points on the charge–discharge curve and are then extracted from the cells at these points for ex situ structural analysis. Analysis of X-ray absorption spectroscopy (both near and fine structure part of the data) data suggests that there are minimal changes to the oxidation state of Mn and S ions during charge–discharge cycles. However, X-ray photoelectron spectroscopy analysis suggests that there are changes in the oxidation state of Mn, which appears to be different from the conclusion drawn from X-ray absorption spectroscopy. This difference in results during cycling can thus be attributed to electrochemical reactions being dominant at the surface of the Li2Mn(SO4)2 particles rather than in the bulk.
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- 2019
20. Nitrogen-Doped Cobalt Phosphide for Enhanced Hydrogen Evolution Activity
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Ling Wang, Stephen J. Pennycook, Sing Teng Chua, Haijun Wu, Shibo Xi, Junmin Xue, Zhi Gen Yu, Fenghe Wang, and Yonghua Du
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Tafel equation ,Materials science ,Inorganic chemistry ,02 engineering and technology ,Electrolyte ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Electron transfer ,Adsorption ,Scanning transmission electron microscopy ,Water splitting ,General Materials Science ,0210 nano-technology - Abstract
Development of highly efficient and durable hydrogen evolution reaction (HER) electrocatalysts has a direct impact on water splitting efficiency and cost-effectiveness. In this work, N-doped CoP2 is successfully synthesized for efficient HER in an alkaline electrolyte, which needs an overpotential of only 64 mV to drive a current density of 10 mA cm-2, with a small Tafel slope of 47.4 mV dec-1 and excellent stability for 15 h without any performance loss in 1 M KOH. This represents one of the best HER catalysts in the alkaline electrolyte so far. The successful doping of N into CoP2 is confirmed using X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and scanning transmission electron microscopy characterizations. It is revealed by first-principle calculations that the partial replacement of P with N not only facilitates electron transfer but also optimizes the Gibbs free energies of H*, H2O, and OH* adsorption on the P active sites, thus facilitating the HER process. This work highlights that anion modification of transition-metal phosphides would be an effective and feasible method to enhance their HER activities and provide new insights for the design of novel HER electrocatalysts.
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- 2019
21. Tuning the Electronic Structure of NiO via Li Doping for the Fast Oxygen Evolution Reaction
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Gaoliang Fu, Renbing Wu, Anton Tadich, Jiaye Zhang, Weiwei Li, Dongchen Qi, Shibo Xi, Jun Cheng, Kelvin H. L. Zhang, Ziliang Chen, Xiaojian Wen, and Yonghua Du
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Materials science ,Absorption spectroscopy ,Photoemission spectroscopy ,General Chemical Engineering ,Non-blocking I/O ,Fermi level ,Oxygen evolution ,02 engineering and technology ,General Chemistry ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Chemical physics ,Materials Chemistry ,symbols ,Density functional theory ,0210 nano-technology ,Perovskite (structure) - Abstract
Transition metal oxides are being actively pursued as low-cost electrocatalysts for the oxygen evolution reaction (OER) in many electrochemical energy devices. A fundamental understanding of the oxide electronic structures, along with the ability to rationally tune them, is a key step toward designing of highly active catalysts. Here, we report the tuning of the electronic structure of NiO via Li doping (LixNi1–xO) to enhance the OER activities. We identified that Li0.5Ni0.5O (LiNiO2) has the highest OER activity, comparable to or exceeding that of the benchmark perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ and LaNiO3. More importantly, a synergistic combination of synchrotron-based photoemission spectroscopy, X-ray absorption spectroscopy, and density functional theory was used to unravel the electronic structure of LixNi1–xO with unprecedented accuracy, thus providing deep insight into the origin of the enhanced catalytic activity. The results unambiguously reveal the creation of a new hole state at 1.1 eV above the Fermi level and an enhanced degree of O 2p–Ni 3d hybridization induced by Li doping optimize the adsorption energetics of OH intermediates and thereby facilitate the fast kinetics for the OER. The LixNi1–xO would serve as a new platform to study the relationship of composition–electronic structure–activity for OER electrocatalysts, beyond the extensively studied Co-based perovskites.
- Published
- 2018
22. High-Magnetization Tetragonal Ferrite-Based Films Induced by Carbon and Oxygen Vacancy Pairs
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Ping Yang, Tun Seng Herng, Xiao Chi, Yang Yang, Andrivo Rusydi, Daqiang Gao, Binghai Liu, Yonghua Du, Wen Xiao, Jun Ding, Yuan Ping Feng, and Wendong Song
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Materials science ,Condensed matter physics ,Doping ,02 engineering and technology ,Coercivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Magnetocrystalline anisotropy ,01 natural sciences ,0104 chemical sciences ,Condensed Matter::Materials Science ,Magnetization ,Tetragonal crystal system ,Ferromagnetism ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Ferrite (magnet) ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,0210 nano-technology - Abstract
Herein, a low-temperature thermal decomposition method is utilized to grow new stable tetragonal Fe3O4-based thick ferrite films. The tetragonal Fe3O4-based film possesses high saturation magnetization of ∼800 emu/cm3. Doping with approximately 10% Co results in a high-energy product of ∼10.9 MGOe with perpendicular magnetocrystalline anisotropy, whereas doping with Ni increases electrical resistivity by a factor of 6 and retains excellent soft magnetic properties (high saturation magnetization and low coercivity). A combined experimental and first-principles study reveals that carbon interstitials (CiB) and oxygen vacancies (VO) form CiB–VO pairs which stabilize the tetragonal phase and enhance saturation magnetization. The magnetization enhancement is further attributed to local ferromagnetic coupling between FeA and FeB induced by CiB–VO pairs in a tetragonal spinel ferrite lattice.
- Published
- 2018
23. Zero-valent Palladium Single-Atoms Catalysts Confined in Black Phosphorus for Efficient Semi-hydrogenation
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Si Chen, Pin Lyu, Chun Zhang, Wei Yu, Ming Joo Koh, Chenliang Su, Chuanhao Yao, Ming Lin, Shibo Xi, Stephen J. Pennycook, Wei Ou, Kah Meng Yam, Jing Li, Xiao Hai, Hanyan Fang, Yonghua Du, Xiaoxu Zhao, Cheng Chen, Haomin Xu, Lu Ma, Jiong Lu, and Junling Lu
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Valence (chemistry) ,Materials science ,Mechanical Engineering ,chemistry.chemical_element ,Heterogeneous catalysis ,Catalysis ,Electronegativity ,Crystallography ,Adsorption ,chemistry ,Mechanics of Materials ,Atom ,General Materials Science ,Density functional theory ,Palladium - Abstract
Single-atom catalysts (SACs) represent a new frontier in heterogeneous catalysis due to their remarkable catalytic properties and maximized atomic utilization. However, single atoms often bond to the support with polarized electron density and thus exhibit a high valence state, limiting their catalytic scopes in many chemical transformations. Here, we demonstrated that two-dimensional (2D) black phosphorus (BP) act as giant phosphorus (P) ligand to confine a high density of single atoms (eg, Pd1, Pt1) via atomic layer deposition. Unlike other 2D materials, BP with relatively low electronegativity and buckled structure favors the strong confinement of robust zero-valent palladium SACs in the vacancy site. Metallic Pd1/P SAC shows a highly selective semi-hydrogenation of phenylacetylene towards styrene, outperforming high-valence Pt1/P SAC, and also distinct from metallic Pd nanoparticles that facilitate the formation of fully hydrogenated products. Our DFT calculations reveal that Pd atom forms covalent-like bonding with adjacent P atoms, wherein H atoms tend to adsorb over electron-rich region for the subsequent hydrogenation. Zero-valent Pd in the confined space favors a larger energy gain for the synthesis of partially-hydrogenated product over the fully-hydrogenated one. Our work provides a new route towards the synthesis of zero-valent SACs on BP for a wide range of organic transformations.
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- 2020
24. Necklace-like Multishelled Hollow Spinel Oxides with Oxygen Vacancies for Efficient Water Electrolysis
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Seeram Ramakrishna, Feng Gong, Dongxiao Ji, Shulei Chou, Tianran Zhang, Yonghua Du, Linlin Li, Zhe Hu, Zhiqiang Zhang, Deshuang Yu, and Shengjie Peng
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Electrolysis ,Electrolysis of water ,Chemistry ,Spinel ,Oxygen evolution ,02 engineering and technology ,General Chemistry ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Chemical engineering ,law ,engineering ,Water splitting ,0210 nano-technology ,Bifunctional - Abstract
The durability and reactivity of catalysts can be effectively and precisely controlled through the careful design and engineering of their surface structures and morphologies. Herein, we develop a novel “adsorption–calcination–reduction” strategy to synthesize spinel transitional metal oxides with a unique necklace-like multishelled hollow structure exploiting sacrificial templates of carbonaceous microspheres, including NiCo2O4 (NCO), CoMn2O4, and NiMn2O4. Importantly, benefiting from the unique structures and reduction treatment to offer rich oxygen vacancies, the unique reduced NCO (R-NCO) as a bifunctional electrocatalyst exhibits the dual characteristics of good stability as well as high electrocatalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). At 1.61 V cell voltage, a 10 mA cm–2 water splitting current density is obtained from the dual-electrode, alkaline water electrolyzer. Calculations based on density functional theory (DFT) reveal a mechanism ...
- Published
- 2018
25. Identifying Influential Parameters of Octahedrally Coordinated Cations in Spinel ZnMnxCo2–xO4 Oxides for the Oxidation Reaction
- Author
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Ye Zhou, Yihu Dai, Yonghua Du, Shibo Xi, Xiao Hu, Shengnan Sun, Ting Wang, Yuanmiao Sun, Zhichuan J. Xu, and Yanhui Yang
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Chemistry ,Spinel ,Inorganic chemistry ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Manganese ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Redox ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Octahedron ,Transition metal ,engineering ,0210 nano-technology ,Cobalt - Abstract
Transition metal oxides are potential alternatives to precious metal catalysts for oxidation reactions. Among these earth abundant oxide catalysts, cobalt- or manganese-based spinel oxides have attracted consistent interest because of their superior catalytic performances. It has been found that the octahedral sites in spinels are responsible for their catalytic activities. However, little is known about the parameters of the octahedrally coordinated cations that influence their activity. Herein, a series of ZnMnxCo2–xO4 (x = 0–2.0) spinel oxides are investigated, employing CO oxidation as the model reaction, with particular attention being paid to the variation in activity caused by tuning the ratio of octahedrally occupied Mn to Co. Both Mn and Co contribute to the activity with Mn cations as the primary active species when they coexist; the intrinsic specific activity is found to be dependent on composition, and the highest activity is seen at a Mn/Co molar ratio of 0.11. The presence of Mn4+ and Mn3+ ...
- Published
- 2018
26. Engineering Sulfur Defects, Atomic Thickness, and Porous Structures into Cobalt Sulfide Nanosheets for Efficient Electrocatalytic Alkaline Hydrogen Evolution
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Yanmei Shi, Yonghua Du, Bin Zhang, Chao Zhang, and Yifu Yu
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Materials science ,Hydrogen ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Cobalt sulfide ,Sulfur ,Exfoliation joint ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Transition metal ,Vacancy defect ,0210 nano-technology - Abstract
The development of nonprecious metal-based electrocatalysts with high mass activity and efficient atom utilization for alkali hydrogen evolution reaction (HER) is of great importance for the preparation of hydrogen resource. The combination of ultrathin and porous structure, especially with the assistance of vacancy, is expected to be beneficial for achievement of high mass activity, but the development of a facile, robust, and generalized strategy to engineer ultrathin, porous, and vacancy-rich structure into nonlayer structured transition metal-based electrocatalysts is highly challenging. Here, we propose a plasma-induced dry exfoliation method to prepare nonlayer structured Co3S4 ultrathin porous nanosheets with abundant sulfur vacancies (Co3S4 PNSvac), which show an onset overpotential of only 18 mV and an extremely large mass activity of 1056.6 A g–1 at an overpotential of 200 mV. Experimental results and theoretical calculations confirm that the efficient alkaline HER performance could be attribute...
- Published
- 2018
27. Single-Atomic Cu with Multiple Oxygen Vacancies on Ceria for Electrocatalytic CO2 Reduction to CH4
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Zheng Chen, Yifei Wang, Zhengxiang Gu, Xin Xu, Gengfeng Zheng, Yonghua Du, and Peng Han
- Subjects
Work (thermodynamics) ,Materials science ,Coordination number ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,Copper ,Oxygen ,Catalysis ,0104 chemical sciences ,chemistry ,Chemical engineering ,Nanorod ,0210 nano-technology ,Mesoporous material - Abstract
The electrocatalytic reduction of CO2 into value-added chemicals such as hydrocarbons has the potential for supplying fuel energy and reducing environmental hazards, while the accurate tuning of electrocatalysts at the ultimate single-atomic level remains extremely challenging. In this work, we demonstrate an atomic design of multiple oxygen vacancy-bound, single-atomic Cu-substituted CeO2 to optimize the CO2 electrocatalytic reduction to CH4. We carried out theoretical calculations to predict that the single-atomic Cu substitution in CeO2(110) surface can stably enrich up to three oxygen vacancies around each Cu site, yielding a highly effective catalytic center for CO2 adsorption and activation. This theoretical prediction is consistent with our controlled synthesis of the Cu-doped, mesoporous CeO2 nanorods. Structural characterizations indicate that the low concentration (
- Published
- 2018
28. Degree of Geometric Tilting Determines the Activity of FeO6 Octahedra for Water Oxidation
- Author
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Haiyan Li, Yonghua Du, Zhichuan J. Xu, Shengnan Sun, Shibo Xi, Jingxian Wang, Yubo Chen, and Yuanmiao Sun
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Materials science ,Electrolysis of water ,General Chemical Engineering ,Spinel ,02 engineering and technology ,General Chemistry ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Degree (temperature) ,Catalysis ,Crystallography ,Octahedron ,Ab initio quantum chemistry methods ,Materials Chemistry ,engineering ,0210 nano-technology - Abstract
Fe oxides and (oxy)hydroxides are promising cost-effective catalysts for scalable water electrolysis. For an improvement in the understanding of the structural factors required by the most active Fe sites, the role of geometric tilting in determining the activity of the FeO6 octahedron for water oxidation was investigated. The catalytic performance of the FeO6 octahedron in a series of crystalline structures, i.e., perovskites AFeO3, spinel ZnFe2O4, and β-FeOOH, was found to be negatively correlated with their octahedral tilting degree. This correlation was rationalized through the Fe–O covalency, which is reflected by the O 2p band center as well as the charge-transfer energy obtained from ab initio calculations. Thus, it was disclosed that FeO6 octahedral tilting alters the activity for water oxidation through changing the covalency degree of Fe–O bonds.
- Published
- 2018
29. Preparation of 1T′-Phase ReS2xSe2(1-x) (x = 0–1) Nanodots for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction
- Author
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Ye Chen, Qinghua Zhang, Chaoliang Tan, Zhimin Luo, Gwang-Hyeon Nam, Yun Zong, Zhicheng Zhang, Christian Kloc, Zhaoning Hu, Thu Ha Tran, Yun Wang, Bo Chen, Bing Li, Shibo Xi, Xiaozhi Liu, Hua Zhang, Lin Gu, Apoorva Chaturvedi, Zhuangchai Lai, Yonghua Du, Ying Huang, School of Materials Science & Engineering, and Center for Programmable Materials
- Subjects
Tafel equation ,Materials [Engineering] ,biology ,Chemistry ,Active site ,02 engineering and technology ,General Chemistry ,Crystal structure ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Crystals ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Phase (matter) ,Vacancy defect ,Crystal Structure ,biology.protein ,Physical chemistry ,Nanodot ,0210 nano-technology - Abstract
As a source of clean energy, a reliable hydrogen evolution reaction (HER) requires robust and highly efficient catalysts. Here, by combining chemical vapor transport and Li-intercalation, we have prepared a series of 1T′-phase ReS2xSe2(1-x) (x = 0–1) nanodots to achieve high-performance HER in acid medium. Among them, the 1T′-phase ReSSe nanodot exhibits the highest hydrogen evolution activity, with a Tafel slope of 50.1 mV dec–1 and a low overpotential of 84 mV at current density of 10 mA cm–2. The excellent hydrogen evolution activity is attributed to the optimal hydrogen absorption energy of the active site induced by the asymmetric S vacancy in the highly asymmetric 1T′ crystal structure. MOE (Min. of Education, S’pore)
- Published
- 2018
30. Operando Investigation of Mn3O4+δ Co-catalyst on Fe2O3 Photoanode: Manganese-Valency-Determined Enhancement at Varied Potentials
- Author
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Joachim Say Chye Loo, Yonghua Du, Chee Keong Ngaw, Ye Zhou, Joel W. Ager, Shibo Xi, Zhichuan J. Xu, Ying Liu, Shengnan Sun, and Chao Wei
- Subjects
Photocurrent ,Materials science ,Valence (chemistry) ,Absorption spectroscopy ,Inorganic chemistry ,Valency ,Oxygen evolution ,Energy Engineering and Power Technology ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Catalysis ,chemistry ,Materials Chemistry ,Electrochemistry ,Chemical Engineering (miscellaneous) ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
The development of efficient catalysts containing earth-abundant elements for the oxygen evolution reaction (OER) in photoelectrochemical (PEC) systems is highly desired for low-cost energy storage and conversion. In this work, mesoporous α-Fe2O3 thin film photoanodes coated with manganese oxide (Mn3O4+δ) co-catalysts are prepared by a dip-coating method. The co-catalyst coating significantly enhances PEC water oxidation performance as compared with the uncoated α-Fe2O3. To understand the origin of this enhancement, in situ X-ray absorption spectroscopy is employed to monitor the valence state of Mn in the Mn3O4+δ co-catalyst as a function of applied potential. It is found that the enhancement of the photocurrent is governed by the Mn valency, and the most prominent enhancement takes place at the valency of ∼3.4+, which is due to the optimal eg electron filling in Mn cations as the electrocatalyst for OER. Our investigation indicates that the contribution of Mn3O4+δ co-catalyst to OER kinetics is variable...
- Published
- 2018
31. Enhanced Catalysis of the Electrochemical Oxygen Evolution Reaction by Iron(III) Ions Adsorbed on Amorphous Cobalt Oxide
- Author
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Luo Gong, Shibo Xi, Boon Siang Yeo, Yonghua Du, and Xin Yu Esther Chng
- Subjects
Tafel equation ,Chemistry ,Inorganic chemistry ,Oxygen evolution ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Linear sweep voltammetry ,Cyclic voltammetry ,0210 nano-technology ,Cobalt oxide - Abstract
The oxygen evolution reaction (OER) is the bottleneck in the efficient production of hydrogen gas fuel via the electrochemical splitting of water. In this work, we present and elucidate the workings of an OER catalytic system which consists of cobalt oxide (CoOx) with adsorbed Fe3+ ions. The CoOx was electrodeposited onto glassy-carbon-disk electrodes, while Fe3+ was added to the 1 M KOH electrolyte. Linear sweep voltammetry and chronopotentiometry were used to assess the system’s OER activity. The addition of Fe3+ significantly lowered the average overpotential (η) required by the cobalt oxide catalyst to produce 10 mA/cm2 O2 current from 378 to 309 mV. The Tafel slope of the CoOx + Fe3+ catalyst also decreased from 59.5 (pure CoOx) to 27.6 mV/dec, and its stability lasted ∼20 h for 10 mA/cm2 O2 evolution. Cyclic voltammetry showed that oxidation of the deposited CoOx, from Co2+ to Co3+ occurred at a more positive potential when Fe3+ was added to the electrolyte. This could be attributed to interactions ...
- Published
- 2017
32. Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film
- Author
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Sherman Jun Rong Tan, Stephen J. Pennycook, Dongyang Wan, Wu Zhou, Dechao Geng, Deyi Fu, Kai Leng, Sokrates T. Pantelides, Jiadong Dan, Yu-Yang Zhang, Zhongxin Chen, Kian Ping Loh, Wei Fu, Zijing Ding, T. Venkatesan, Yonghua Du, Peng Song, and Xiaoxu Zhao
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Materials science ,Nanoporous ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,Edge (geometry) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,law.invention ,Crystallography ,chemistry.chemical_compound ,Unpaired electron ,chemistry ,law ,General Materials Science ,Density functional theory ,Electron microscope ,0210 nano-technology ,Porosity ,Molybdenum disulfide ,Molecular beam epitaxy - Abstract
The catalytic and magnetic properties of molybdenum disulfide (MoS2) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated ed...
- Published
- 2017
33. Revealing the Dominant Chemistry for Oxygen Reduction Reaction on Small Oxide Nanoparticles
- Author
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Yonghua Du, Jingxian Wang, Zhichuan J. Xu, Shibo Xi, Chao Wei, Ye Zhou, Zhenxing Feng, Shengnan Sun, School of Materials Science and Engineering, Solar Fuels Laboratory, and Energy Research Institute @ NTU (ERI@N)
- Subjects
Valence (chemistry) ,Materials [Engineering] ,Chemistry ,Surface Density ,Oxide ,Valency ,Nanoparticle ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Metal ,chemistry.chemical_compound ,Chemical engineering ,Mn Valence State ,visual_art ,visual_art.visual_art_medium ,Ferrite (magnet) ,0210 nano-technology - Abstract
The bulk chemistry has been successfully used as a descriptor for oxygen reduction reaction (ORR) activities of various metal oxides. However, as the size of oxides becomes small, the bulk chemistry may not be sufficient to describe the activities. Here, we report a systematic study on Mn-substituted ferrite MnxFe3–xO4 (x = 0.5–2.5) nanoparticles and the roles of surface Mn in determining their ORR activities. Gradual Mn substitution induced changes in Mn valence and crystal structure. However, there is no remarkable correlation that can be found between their bulk chemistry and ORR activities. Instead, the surface Mn density and valency were found to play dominant roles in determining the ORR. This work shows that, at a small particle size, the bulk chemistry of oxides may not be the descriptor for their electrochemical properties. Due to the significantly high surface/bulk ratio, the surface chemistry has to be carefully characterized to interpret the activities of oxide nanoparticles. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)
- Published
- 2017
34. Zero-valent Palladium Single-Atoms Catalysts Confined in Black Phosphorus for Efficient Semi-hydrogenation
- Author
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chen, cheng, primary, Wei, Ou, primary, Kahmeng, Yam, primary, Shibo, Xi, primary, Xiaoxu, Zhao, primary, Si, Chen, primary, Li, Jing, primary, Pin, Lvy, primary, Lu, Ma, primary, Haomin, Xu, primary, Wei, Yu, primary, Hanyan, Fang, primary, Chuanhao, Yao, primary, Xiao, Hai, primary, Koh, Ming Joo, primary, Ming, Lin, primary, Pennycook, Stephen J., primary, Junling, Lu, primary, Yonghua, Du, primary, Chenliang, Su, primary, Chun, Zhang, primary, and Lu, Jiong, primary
- Published
- 2020
- Full Text
- View/download PDF
35. Phosphonate-Based Metal–Organic Framework Derived Co–P–C Hybrid as an Efficient Electrocatalyst for Oxygen Evolution Reaction
- Author
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Zhong Chen, Wenguang Tu, Rong Xu, Armando Borgna, Yonghua Du, Danping Wang, Shengming Yin, and Tianhua Zhou
- Subjects
inorganic chemicals ,Inorganic chemistry ,Oxygen evolution ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,Phosphonate ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Metal-organic framework ,0210 nano-technology ,Cobalt ,Cobalt phosphate - Abstract
Cobalt phosphate is considered to be one of the most active catalysts for the oxygen evolution reaction (OER) in neutral or near-neutral pH media, but only a few transition-metal phosphates are investigated in alkaline media, probably due to their poor intrinsic electrical conductivity and/or tendency to aggregate. Herein, in situ-formed cobalt phosphate decorated with N-doped graphitic carbon was prepared using phosphonate-based metal–organic frameworks (MOFs) as the precursor. It can serve as a highly active OER catalyst in alkaline media, affording a current density of 10 mA cm–2 at a small overpotential of 215 mV on the Ni foam. A combination of X-ray absorption spectroscopy and high-resolution XPS elucidates the origin of the high activity. Our observations unveil that cobalt diphosphate having the distorted metal coordination geometry with long Co–O and Co–Co distances is mainly responsible for the high OER activity. These results not only demonstrate the potential of a low-cost OER catalyst derived...
- Published
- 2017
36. Unleashing the Power and Energy of LiFePO4-Based Redox Flow Lithium Battery with a Bifunctional Redox Mediator
- Author
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Li Fan, Yonghua Du, Qing Wang, Chuankun Jia, Xingzhu Wang, Mingyue Zhou, and Yun Guang Zhu
- Subjects
Battery (electricity) ,Chemistry ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Redox ,Flow battery ,Catalysis ,Energy storage ,Lithium battery ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,0210 nano-technology ,Bifunctional ,Power density ,Voltage - Abstract
Redox flow batteries, despite great operation flexibility and scalability for large-scale energy storage, suffer from low energy density and relatively high cost as compared to the state-of-the-art Li-ion batteries. Here we report a redox flow lithium battery, which operates via the redox targeting reactions of LiFePO4 with a bifunctional redox mediator, 2,3,5,6-tetramethyl-p-phenylenediamine, and presents superb energy density as the Li-ion battery and system flexibility as the redox flow battery. The battery has achieved a tank energy density as high as 1023 Wh/L, power density of 61 mW/cm2, and voltage efficiency of 91%. Operando X-ray absorption near-edge structure measurements were conducted to monitor the evolution of LiFePO4, which provides insightful information on the redox targeting process, critical to the device operation and optimization.
- Published
- 2017
37. Activating and Optimizing Activity of CoS2 for Hydrogen Evolution Reaction through the Synergic Effect of N Dopants and S Vacancies
- Author
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Jun Ding, Wen Xiao, Pinxian Xi, Daqiang Gao, Jingyan Zhang, Shibo Xi, and Yonghua Du
- Subjects
Tafel equation ,Materials science ,Dopant ,Renewable Energy, Sustainability and the Environment ,Doping ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Fuel Technology ,chemistry ,Chemical engineering ,Chemistry (miscellaneous) ,Materials Chemistry ,Density functional theory ,0210 nano-technology ,Cobalt - Abstract
Here, N-doped cobalt pyrite (CoS2) electrocatalytic material is developed via utilizing the synergic effect of N dopants and S vacancies. The catalyst displays high activity and stability for hydrogen evolution reaction. Density functional theory calculations and electrochemical characterizations reveal that the electrochemical activity of the CoS2 catalyst is directly associated with the content of N dopants and S vacancies, where proper combinations of N dopants and S vacancies yield a minimized overpotential close to that of commercial Pt. What’s more, optimized performance has been achieved by carefully manipulating the amounts of N dopants and S vacancies in N-doped CoS2 catalyst, which exhibits a Tafel slope as small as 48 mV/dec, an ultralow overpotential of 57 mV at 10 mA/cm2, and satisfying stability. This work highlights a feasible strategy to explore efficient electrocatalysts via nonmetal element doping and defect engineering.
- Published
- 2017
38. Intrinsically Conductive Perovskite Oxides with Enhanced Stability and Electrocatalytic Activity for Oxygen Reduction Reactions
- Author
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Bing Li, Xiaoming Ge, Hua Zhang, T. S. Andy Hor, Melinda Sindoro, Yun Zong, Zhaolin Liu, and Yonghua Du
- Subjects
Tafel equation ,Potassium hydroxide ,Reaction mechanism ,Aqueous solution ,Inorganic chemistry ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Cyclic voltammetry ,0210 nano-technology ,Perovskite (structure) - Abstract
The oxygen reduction reaction (ORR) is traditionally catalyzed by carbon-supported precious metals, heteroatom-doped carbons, and transition-metal–carbon hybrids. Despite their good electric conductivity and high catalytic activities, these carbon-containing catalysts suffer from electrochemical carbon corrosion which limits their utility in metal–air batteries and fuel cells. Here, we report a class of perovskite La0.5Sr0.5Mn1–xNixO3−δ nanocrystals that are intrinsically conductive with good electrocatalytic activity for the ORR. Among these perovskites, La0.5Sr0.5Mn0.9Ni0.1O3−δ (δ = 0.06, LSMN) exhibited the highest electrocatalytic activity for ORR with an onset potential of 1.02 V, a half-wave potential of 0.80 V, and a Tafel slope of −68 mV decade–1 in 0.1 M potassium hydroxide aqueous solution. Negligible degradation of oxygen reduction currents was observed after 300 cyclic voltammetry scans from 1.08 to 0.15 V. We demonstrated that the electrically conductive perovskites with transition-metal redo...
- Published
- 2016
39. One-Pot Synthesis of Fe(III)–Polydopamine Complex Nanospheres: Morphological Evolution, Mechanism, and Application of the Carbonized Hybrid Nanospheres in Catalysis and Zn–Air Battery
- Author
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Xuehong Lu, Boon Ying Tay, Jia Ming Ang, Yonghua Du, Junhua Kong, Ludger P. Stubbs, and Chenyang Zhao
- Subjects
Nanostructure ,Morphology (linguistics) ,Carbonization ,Chemistry ,One-pot synthesis ,02 engineering and technology ,Surfaces and Interfaces ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Polymerization ,Polymer chemistry ,Electrochemistry ,medicine ,Ferric ,General Materials Science ,Absorption (chemistry) ,0210 nano-technology ,Spectroscopy ,medicine.drug - Abstract
We report one-pot synthesis of Fe(III)-polydopamine (PDA) complex nanospheres, their structures, morphology evolution, and underlying mechanism. The complex nanospheres were synthesized by introducing ferric ions into the reaction mixture used for polymerization of dopamine. It is verified that both the oxidative polymerization of dopamine and Fe(III)-PDA complexation contribute to the "polymerization" process, in which the ferric ions form coordination bonds with both oxygen and nitrogen, as indicated by X-ray absorption fine-structure spectroscopy. In the "polymerization" process, the morphology of the complex nanostructures is gradually transformed from sheetlike to spherical at the feed Fe(III)/dopamine molar ratio of 1/3. The final size of the complex spheres is much smaller than its neat PDA counterpart. At higher feed Fe(III)/dopamine molar ratios, the final morphology of the "polymerization" products is sheetlike. The results suggest that the formation of spherical morphology is likely to be driven by covalent polymerization-induced decrease of hydrophilic functional groups, which causes reself-assembly of the PDA oligomers to reduce surface area. We also demonstrate that this one-pot synthesis route for hybrid nanospheres enables the facile construction of carbonized PDA (C-PDA) nanospheres uniformly embedded with Fe3O4 nanoparticles of only 3-5 nm in size. The C-PDA/Fe3O4 nanospheres exhibit catalytic activity toward oxygen reduction reaction and deliver a stable discharge voltage for over 200 h when utilized as the cathode in a primary Zn-air battery and are also good recyclable catalyst supports.
- Published
- 2016
40. Oxygen Tuned Local Structure and Phase-Change Performance of Germanium Telluride
- Author
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Xilin Zhou, Yonghua Du, Liangcai Wu, Zhitang Song, Jitendra K. Behera, and Robert E. Simpson
- Subjects
010302 applied physics ,Materials science ,Doping ,Enthalpy ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Oxygen ,Phase-change memory ,chemistry.chemical_compound ,symbols.namesake ,Crystallography ,chemistry ,Chemical physics ,Molecular vibration ,0103 physical sciences ,symbols ,General Materials Science ,0210 nano-technology ,Raman spectroscopy ,Germanium telluride - Abstract
The effect of oxygen on the local structure of Ge atoms in GeTe-O materials has been investigated. Oxygen leads to a significant modification to the vibrational modes of Ge octahedra, which results from a decrease in its coordination. We find that a defective octahedral Ge network is the crucial fingerprint for rapid and reversible structural transitions in GeTe-based phase change materials. The appearance of oxide Raman modes confirms phase separation into GeO and TeO at high level O doping. Counterintuitively, despite the increase in crystallization temperature of oxygen doped GeTe-O phase change materials, when GeTe-O materials are used in electrical phase change memory cells, the electrical switching energy is lower than the pure GeTe material. This switching energy reduction is ascribed to the smaller change in volume, and therefore smaller enthalpy change, for the oxygen doped GeTe materials.
- Published
- 2016
41. In Situ Raman Spectroscopy of Copper and Copper Oxide Surfaces during Electrochemical Oxygen Evolution Reaction: Identification of CuIII Oxides as Catalytically Active Species
- Author
-
Shibo Xi, Albertus D. Handoko, Boon Siang Yeo, Yonghua Du, and Yilin Deng
- Subjects
Copper oxide ,Inorganic chemistry ,Oxygen evolution ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Chronoamperometry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,Catalysis ,0104 chemical sciences ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,Linear sweep voltammetry ,symbols ,Cyclic voltammetry ,0210 nano-technology ,Raman spectroscopy - Abstract
Scanning electron microscopy, X-ray diffraction, cyclic voltammetry, chronoamperometry, in situ Raman spectroscopy, and X-ray absorption near-edge structure spectroscopy (XANES) were used to investigate the electrochemical oxygen evolution reaction (OER) on Cu, Cu2O, Cu(OH)2, and CuO catalysts. Aqueous 0.1 M KOH was used as the electrolyte. All four catalysts were oxidized or converted to CuO and Cu(OH)2 during a slow anodic sweep of cyclic voltammetry and exhibited similar activities for the OER. A Raman peak at 603 cm–1 appeared for all the four samples at OER-relevant potentials, ≥1.62 V vs RHE. This peak was identified as the Cu–O stretching vibration band of a CuIII oxide, a metastable species whose existence is dependent on the applied potential. Since this frequency matches well with that from a NaCuIIIO2 standard, we suggest that the chemical composition of the CuIII oxide is CuO2–-like. The four catalysts, in stark contrast, did not oxidize the same way during direct chronoamperometry measurement...
- Published
- 2016
42. β-FeOOH: An Earth-Abundant High-Capacity Negative Electrode Material for Sodium-Ion Batteries
- Author
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Linghui Yu, Luyuan Paul Wang, Ping Yang, Shibo Xi, Zhichuan J. Xu, Yonghua Du, and Madhavi Srinivasan
- Subjects
Battery (electricity) ,Materials science ,Abundance (chemistry) ,General Chemical Engineering ,Sodium ,chemistry.chemical_element ,General Chemistry ,Electrolyte ,Overpotential ,Kinetic energy ,Redox ,Anode ,Chemical engineering ,chemistry ,Materials Chemistry ,Forensic engineering - Abstract
Thanks to the great earth abundance and excellent energy density of sodium, sodium-ion batteries are promising alternative energy storage devices for large-scale applications. Developing cheap, safe, and high-capacity sodium-ion battery anode materials is one of the critical challenges in this field. Here, we show that β-FeOOH is a very promising low-cost anode material, with a high reversible capacity (>500 mAh g–1 during initial cycles). The fundamental characteristics associated with the discharge/charge processes, in terms of the redox reactions, formation/deformation of the solid electrolyte interface (SEI) layers, and structural and morphological changes, are comprehensively investigated. In addition, a comparison study shows that the smaller-sized FeOOH has more serious kinetic restrictions, and thus lower capacities, while it shows better cyclability than the bigger one. Origins of the large overpotential are discussed, and it is suggested that the overpotential should be mainly due to the feature...
- Published
- 2015
43. Spatial Imaging and Speciation of Lead in the Accumulator Plant Sedum alfredii by Microscopically Focused Synchrotron X-ray Investigation
- Author
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Lingli Lu, Shengke Tian, Yonghua Du, Samuel M. Webb, Xiaoe Yang, and Patrick O. Brown
- Subjects
media_common.quotation_subject ,Sedum ,Metal ,Absorptiometry, Photon ,Botany ,Soil Pollutants ,Environmental Chemistry ,Hyperaccumulator ,media_common ,Plant Stems ,biology ,Extended X-ray absorption fine structure ,Ecotype ,Spectrometry, X-Ray Emission ,General Chemistry ,biology.organism_classification ,Vascular bundle ,Crassulaceae ,Plant Leaves ,Speciation ,X-Ray Absorption Spectroscopy ,Lead ,visual_art ,Sedum alfredii ,visual_art.visual_art_medium ,Synchrotrons - Abstract
Sedum alfredii (Crassulaceae), a species native to China, has been characterized as a Zn/Cd cohyperaccumulator and Pb accumulator though the mechanisms of metal tolerance and accumulation are largely unknown. Here, the spatial distribution and speciation of Pb in tissues of the accumulator plant was investigated using synchrotron-based X-ray microfluorescence and powder Extended X-ray absorption fine structure (EXAFS) spectroscopy. Lead was predominantly restricted to the vascular bundles of both leaf and stem of the accumulator. Micro-XRF analysis revealed that Pb distributed predominantly within the areas of vascular bundles, and a positive correlation between the distribution patterns of S and Pb was observed. The dominant chemical form of Pb (>60%) in tissues of both accumulating (AE) and nonaccumulating ecotype (NAE) S. alfredii was similar to prepared Pb-cell wall compounds. However, the percentage of the Pb-cell wall complex is lower in the stem and leaf of AE, and a small amount of Pb appeared to be associated with SH-compounds. These results suggested a very low mobility of Pb out of vascular bundles, and that the metal is largely retained in the cell walls during transportation in plants of S. alfredii.
- Published
- 2010
Catalog
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