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8. Surface Van Hove Singularity Enabled Efficient Catalysis: The Cases of CO Oxidation and Hydrogen Evolution Reactions

Author

Liu, Liangliang, Wang, Chunyan, Zhang, Liying, Liu, Chengyan, Niu, Chunyao, Zeng, Zaiping, Ma, Dongwei, and Jia, Yu

Subjects
Condensed Matter - Materials Science
Abstract

Surface Van Hove singularity (SVHS), defined as the surface states near the Fermi level (EF) in low-dimensional systems, triggers exciting physical phenomena distinct from bulk. We herein explore theoretically the potential role of SVHS in catalysis taking CO oxidation reaction as prototype over graphene/Ca2N (Gra/Ca2N) heterojunction and Pt2HgSe3 (001) surface. It is demonstrated that both systems with SVHS could serve as an electron bath to promote O2 adsorption and subsequent CO oxidation with low energy barriers of 0.2 ~ 0.6 eV for Gra/Ca2N and Pt2HgSe3 (001) surface. Importantly, the catalytically active sites associated with SVHS are well-defined and uniformly distributed over the whole surface plane, which is superior to the commonly adopted defect or doping strategy, and further the chemical reactivity of SVHS also can be tuned easily via adjusting its position with respect to EF. Our study demonstrates the enabling power of SVHS, and provides novel physical insights into the promising potential role of VHS in designing high-efficiency catalysts.

Published
2021

15. Structural Stability and Defect-Tolerance of Ionic Spinel Semiconductor for High-Efficiency Solar Cells

Author

Liang, Hanzhen, Xiang, Huiwen, Zhu, Rui, Liu, Chengyan, and Jia, Yu

Subjects
Condensed Matter - Materials Science
Abstract

The incompatibility between defect-tolerance and structural stability is a severe issue hindering the wide application of high-efficiency solar cells. Usually, covalent/polar semiconductors with prototype of Si/CdTe crystals exhibit great structural stability owing to their compactly composed tetrahedral building blocks, but present extremely poor defect-tolerance due to the similar electronegativity of component elements. On the contrary, ionic semiconductors, such as perovskite series, always exhibit benign electronic properties of intrinsic defects owing to the great disparity of electronegativity between anions and cations, but are structurally unstable because of the sparsely composed octahedral building blocks supported by large cations. Combining the stable framework of covalent semiconductors and benign defects of ionic compounds, we find that HgX2S4 (X=In, Sc and Y) spinel semiconductors possess both the merits. The tightly combined tetrahedral and octahedral blocks ensures the structural stability, and the band edge of ionic characteristic, which is mainly dominated by Hg-6s and S-3p orbitals for conduction band minimum (CBM) and valence band maximum (VBM), respectively, makes HgX2S4 defect-tolerant. The prominent downward bending of CBM caused by spatially spreading Hg-6s spherical orbital not only induces a suitable optical band gap which is often too large in ionic compounds, but also promotes the formation and transport of n-type carriers. This study presents that Hg-based chalcogenide spinels are promising candidates for high-efficiency solar cells, and suggests that adopting cations with delocalized orbitals under the framework of spinel crystal is an alternative way for synthesizing the stable and defect-tolerant photovoltaic materials., Comment: 9 figures, 22 pages

Published
2021

16. Tropical teleconnection impacts on Antarctic climate changes

Author

Li, Xichen, Cai, Wenju, Meehl, Gerald A, Chen, Dake, Yuan, Xiaojun, Raphael, Marilyn, Holland, David M, Ding, Qinghua, Fogt, Ryan L, Markle, Bradley R, Wang, Guojian, Bromwich, David H, Turner, John, Xie, Shang-Ping, Steig, Eric J, Gille, Sarah T, Xiao, Cunde, Wu, Bingyi, Lazzara, Matthew A, Chen, Xianyao, Stammerjohn, Sharon, Holland, Paul R, Holland, Marika M, Cheng, Xiao, Price, Stephen F, Wang, Zhaomin, Bitz, Cecilia M, Shi, Jiuxin, Gerber, Edwin P, Liang, Xi, Goosse, Hugues, Yoo, Changhyun, Ding, Minghu, Geng, Lei, Xin, Meijiao, Li, Chuanjin, Dou, Tingfeng, Liu, Chengyan, Sun, Weijun, Wang, Xinyue, and Song, Chentao

Subjects
Climate Action
Abstract

Over the modern satellite era, substantial climatic changes have been observed in the Antarctic, including atmospheric and oceanic warming, ice sheet thinning and a general Antarctic-wide expansion of sea ice, followed by a more recent rapid loss. Although these changes, featuring strong zonal asymmetry, are partially influenced by increasing greenhouse gas emissions and stratospheric ozone depletion, tropical–polar teleconnections are believed to have a role through Rossby wave dynamics. In this Review, we synthesize understanding of tropical teleconnections to the Southern Hemisphere extratropics arising from the El Niño–Southern Oscillation, Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation, focusing on the mechanisms and long-term climatic impacts. These teleconnections have contributed to observed Antarctic and Southern Ocean changes, including regional rapid surface warming, pre-2015 sea ice expansion and its sudden reduction thereafter, changes in ocean heat content and accelerated thinning of most of the Antarctic ice sheet. However, due to limited observations and inherent model biases, uncertainties remain in understanding and assessing the importance of these teleconnections versus those arising from greenhouse gases, ozone recovery and internal variability. Sustained pan-Antarctic efforts towards long-term observations, and more realistic dynamics and parameterizations in high-resolution climate models, offer opportunities to reduce these uncertainties.

Published
2021

24. Multifunctional 2D CuSe monolayer nanodevice

Author

An, Yipeng, Hou, Yusheng, Wang, Hui, Li, Jie, Wu, Ruqian, Liu, Chengyan, Wang, Tianxing, and Jiao, Jutao

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

In a very recent experimental work [Gao et al., 2018 Adv. Mater. 30, 1707055], a graphene-like CuSe monolayer was realized. Motivated by this success, we performed first-principles calculations to investigate its electronic transport and photoelectronic properties. We find that the CuSe ML shows a strong electrical anisotropy, and its current-voltage (I-V) curves along the zigzag and armchair directions are noticeably different. The CuSe ML also displays a useful negative differential resistance (NDR) effect along the both directions when the bias is beyond 1.0 V. Moreover, it has a large photon absorption to orange light. Our study suggests that CuSe ML is a multifunctional material and has various potential applications in electrical-anisotropy-based, NDR-based, and even optical nanodevices., Comment: Journal of Physics: Condensed Matter 2019

Published
2019
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27. Negative differential conductance effect and electrical anisotropy of 2D ZrB2 monolayers

Author

An, Yipeng, Jiao, Jutao, Hou, Yusheng, Wang, Hui, Wu, Ruqian, Liu, Chengyan, Chen, Xuenian, Wang, Tianxing, and Wang, Kun

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Two-dimensional (2D) metal-diboride ZrB2 monolayers was predicted theoretically as a stable new electronic material [A. Lopez-Bezanilla, Phys. Rev. Mater., 2018, 2, 011002 (R)]. Here, we investigate its electronic transport properties along the zigzag (z-ZrB2) and armchair (a-ZrB2) directions, using the density functional theory and non-equilibrium Green's function methods. Under low biases, the 2D ZrB2 shows a similar electrical transport along zigzag and armchair directions as electric current propagates mostly via the metallic Zr-Zr bonds. However, it shows an electrical anistropy under high biases, and its I-V curves along zigzag and armchair directions diverge as the bias voltage is higher than 1.4 V, as more directional B-B transmission channels are opened. Importantly, both z-ZrB2 and a-ZrB2 show a pronounced negative differential conductance (NDC) effect and hence they can be promising for the use in NDC-based nanodevices.

Published
2018
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37. Southern Ocean Ice Prediction System version 1.0 (SOIPS v1.0): description of the system and evaluation of synoptic-scale sea ice forecasts.

Author

Zhao, Fu, Liang, Xi, Tian, Zhongxiang, Li, Ming, Liu, Na, and Liu, Chengyan

Subjects
SEA ice drift, STANDARD deviations, ANTARCTIC exploration, NAVIGATION in shipping, ANTARCTIC ice, KALMAN filtering, SEA ice, ICE shelves
Abstract

An operational synoptic-scale sea ice forecasting system for the Southern Ocean, namely the Southern Ocean Ice Prediction System (SOIPS), has been developed to support ship navigation in the Antarctic sea ice zone. Practical application of the SOIPS forecasts had been implemented for the 38th Chinese National Antarctic Research Expedition for the first time. The SOIPS is configured on an Antarctic regional sea ice–ocean–ice shelf coupled model and an ensemble-based localized error subspace transform Kalman filter data assimilation model. Daily near-real-time satellite sea ice concentration observations are assimilated into the SOIPS to update sea ice concentration and thickness in the 12 ensemble members of the model state. By evaluating the SOIPS performance in forecasting sea ice metrics in a complete melt–freeze cycle from 1 October 2021 to 30 September 2022, this study shows that the SOIPS can provide reliable Antarctic sea ice forecasts. In comparison with non-assimilated EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) data, annual mean root mean square errors in the sea ice concentration forecasts at a lead time of up to 168 h are lower than 0.19, and the integrated ice edge errors in the sea ice forecasts in most freezing months at lead times of 24 and 72 h maintain around 0.5×106 km 2 and below 1.0×106 km 2 , respectively. With respect to the scarce Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) observations, the mean absolute errors in the sea ice thickness forecasts at a lead time of 24 h are lower than 0.3 m, which is in the range of the ICESat-2 uncertainties. Specifically, the SOIPS has the ability to forecast sea ice drift, in both magnitude and direction. The derived sea ice convergence rate forecasts have great potential for supporting ship navigation on a fine local scale. The comparison between the persistence forecasts and the SOIPS forecasts with and without data assimilation further shows that both model physics and the data assimilation scheme play important roles in producing reliable sea ice forecasts in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Published
2024
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44. Synergistic Densification in Hybrid Organic‐Inorganic MXenes for Optimized Photothermal Conversion.

Author

Xu, Tong, Tan, Shujuan, Li, Shaoxiong, Chen, Tianyu, Wu, Yue, Hao, Yilin, Liu, Chengyan, and Ji, Guangbin

Subjects
PHOTOTHERMAL conversion, SURFACE plasmon resonance, ELECTRON transport, FERMI level
Abstract

Optimizin the efficient light‐trapping in the photothermal conversion by enhancing localized surface plasmon resonance (LSPR) is crucial in improving light‐heat‐conversion efficiency of Ti3C2Tx MXene. However, its susceptibility to oxidation makes it prone to oxides formation, diminishing its metallic properties and significantly reducing the LSPR effect. This work synthesizes a kind of air‐stable hybrid Ti3C2Tx MXenes by a synergistic densification strategy that incorporates sulfhydryl‐bonding between organic and inorganic parts by reacting Ti3C2Tx MXene with thiocarboxylic acids. The resultant shortening of electron transport pathways, enhanced charge density, and the generation of additional electronic states around the Fermi level collectively contribute to an augmented LSPR effect. Additionally, the hybrid Ti3C2Tx MXenes also demonstrate high‐temperature resistance and reduced water interactions. These combined effects substantially elevate photothermal conversion efficiency through thiocarboxylic acids modification, reaching a photothermal evaporation rate of 1.77 kg m−2 h−1 with 94.56% efficiency in hybrid Ti3C2Tx MXenes. The approach paves the way for the design and development of a three‐in‐one strategy for photothermal conversion. [ABSTRACT FROM AUTHOR]

Published
2024
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48. Transport of Anthropogenic Carbon From the Antarctic Shelf to Deep Southern Ocean Triggers Acidification

Author

Zhang, Shuang, primary, Wu, Yingxu, additional, Cai, Wei‐Jun, additional, Cai, Wenju, additional, Feely, Richard A., additional, Wang, Zhaomin, additional, Tanhua, Toste, additional, Wang, Yanmin, additional, Liu, Chengyan, additional, Li, Xichen, additional, Yang, Qinghua, additional, Ding, Minghu, additional, Xu, Zhongsheng, additional, Kerr, Rodrigo, additional, Luo, Yiming, additional, Cheng, Xiao, additional, Chen, Liqi, additional, and Qi, Di, additional

Published
2023
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