Yanan Wang

Bio: Yanan Wang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Medicine & Catalysis. The author has an hindex of 9, co-authored 20 publications receiving 214 citations. Previous affiliations of Yanan Wang include University of Science and Technology of China & Dalian Institute of Chemical Physics.

Ab initio nonadiabatic molecular dynamics investigations on the excited carriers in condensed matter systems

Abstract: The ultrafast dynamics of photoexcited charge carriers in condensed matter systems play an important role in optoelectronics and solar energy conversion. Yet it is challenging to understand such multidimensional dynamics at the atomic scale. Combining the real‐time time‐dependent density functional theory with fewest‐switches surface hopping scheme, we develop time‐dependent ab initio nonadiabatic molecular dynamics (NAMD) code Hefei‐NAMD to simulate the excited carrier dynamics in condensed matter systems. Using this method, we have investigated the interfacial charge transfer dynamics, the electron–hole recombination dynamics, and the excited spin‐polarized hole dynamics in different condensed matter systems. The time‐dependent dynamics of excited carriers are studied in energy, real and momentum spaces. In addition, the coupling of the excited carriers with phonons, defects and molecular adsorptions are investigated. The state‐of‐art NAMD studies provide unique insights to understand the ultrafast dynamics of the excited carriers in different condensed matter systems at the atomic scale.

Multiple heterointerfaces boosted de-/sodiation kinetics towards superior Na storage and Na-Ion full battery

Abstract: In this article, an effective strategy (viz., constructing multiple heterointerfaces) is proposed to develop superior electrode materials for sodium-ion battery (SIB), which is the most promising alternative to market-dominant lithium-ion battery for stationary energy storage. In the as-prepared heterogeneous-SnO2/Se/graphene (h-SSG) composite, there exists multiple phase interfaces, including heterointerfaces between tetragonal and orthorhombic SnO2 (t-/o-SnO2) in the heterogeneous SnO2 nanojunctions and two phase interfaces between t/o-SnO2 and amorphous Se. These multiple phase interfaces promise the much improved Na storage properties of h-SSG when compared to four controls without such multiple heterointerfaces because the multiple built-in electric fields at the heterointerfaces can significantly boost the surface reaction kinetics and facilitate charge transport as demonstrated by kinetics analyses, theoretical calculations and contrastive electrochemical tests. Moreover, h-SSG also exhibits superior Na-ion full cell performance when coupled with a high-voltage Na3V2(PO4)2O2F cathode. In view of the universality of the heterointerface-based enhancement effect on surface reaction and charge transport kinetics and the facile preparation procedures, the present strategy should be universal to develop other superior electrode materials for high-performance SIBs and other batteries for future energy storage applications.

Ambient-pressure hydrogenation of CO2 into long-chain olefins

Abstract: Abstract The conversion of CO 2 by renewable power-generated hydrogen is a promising approach to a sustainable production of long-chain olefins (C 4+ = ) which are currently produced from petroleum resources. The decentralized small-scale electrolysis for hydrogen generation requires the operation of CO 2 hydrogenation in ambient-pressure units to match the manufacturing scales and flexible on-demand production. Herein, we report a Cu-Fe catalyst which is operated under ambient pressure with comparable C 4+ = selectivity (66.9%) to that of the state-of-the-art catalysts (66.8%) optimized under high pressure (35 bar). The catalyst is composed of copper, iron oxides, and iron carbides. Iron oxides enable reverse-water-gas-shift to produce CO. The synergy of carbide path over iron carbides and CO insertion path over interfacial sites between copper and iron carbides leads to efficient C-C coupling into C 4+ = . This work contributes to the development of small-scale low-pressure devices for CO 2 hydrogenation compatible with sustainable hydrogen production.

Synthesis and catalytic application of FER zeolites with controllable size

Abstract: The crystal size of zeolites has an enormous effect on zeolite properties and catalytic performance. Herein, a direct hydrothermal synthesis method to control the size of FER zeolites, by using piperidine (PI) as the structure directing agent (SDA) assisted by cetyltrimethyl ammonium bromide (CTAB), is developed. All the resultant FER samples possess high crystallinity, while their crystal sizes range from ∼100 nm to ∼2 μm. The effect of CTAB in the synthesis gel on the physicochemical properties, especially the crystal sizes, and the 1-butene skeletal isomerization performance of FER zeolites was investigated. The addition of CTAB has an obvious effect on the formation of FER zeolites, and the hydrophobic tail of CTAB can restrict the excessive growth of FER leading to the formation of highly crystallized FER with various crystal sizes. The nano-scale FER shows higher initial 1-butene conversion and better catalytic stability than micron-sized FER, which is mainly related to the superior accessibility of acid sites, larger external surface area, and less diffusion limitation due to the decrease of the crystal size. This novel synthesis strategy provides an effective way to regulate the size and performance of FER zeolites, and a new function of CTAB in the synthesis of zeolites is developed.

K Atom Promotion of O2 Chemisorption on Au(111) Surface.

Abstract: Alkali atoms are known to promote or poison surface catalytic chemistry. To explore alkali promotion of catalysis and to characterize discharge species in alkali-oxygen batteries, we examine coadso...

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

MoS2 Nanosheets Vertically Aligned on Carbon Paper: A Freestanding Electrode for Highly Reversible Sodium Ion Batteries

Abstract: The development of sodium-ion batteries for large-scale applications requires the synthesis of electrode materials with high capacity, high initial Coulombic efficiency (ICE), high rate performance, long cycle life, and low cost. A rational design of freestanding anode materials is reported for sodium-ion batteries, consisting of molybdenum disulfide (MoS2) nanosheets aligned vertically on carbon paper derived from paper towel. The hierarchical structure enables sufficient electrode/electrolyte interaction and fast electron transportation. Meanwhile, the unique architecture can minimize the excessive interface between carbon and electrolyte, enabling high ICE. The as-prepared MoS2@carbon paper composites as freestanding electrodes for sodium-ion batteries can liberate the traditional electrode manufacturing procedure, thereby reducing the cost of sodium-ion batteries. The freestanding MoS2@carbon paper electrode exhibits a high reversible capacity, high ICE, good cycling performance, and excellent rate capability. By exploiting in situ Raman spectroscopy, the reversibility of the phase transition from 2H-MoS2 to 1T-MoS2 is observed during the sodium-ion intercalation/deintercalation process. This work is expected to inspire the development of advanced electrode materials for high-performance sodium-ion batteries.

Self-Supporting, Flexible, Additive-Free, and Scalable Hard Carbon Paper Self-Interwoven by 1D Microbelts: Superb Room/Low-Temperature Sodium Storage and Working Mechanism.

Abstract: Hard carbon is regarded as a promising anode material for sodium-ion batteries (SIBs). However, it usually suffers from the issues of low initial Coulombic efficiency (ICE) and poor rate performance, severely hindering its practical application. Herein, a flexible, self-supporting, and scalable hard carbon paper (HCP) derived from scalable and renewable tissue is rationally designed and prepared as practical additive-free anode for room/low-temperature SIBs with high ICE. In ether electrolyte, such HCP achieves an ICE of up to 91.2% with superior high-rate capability, ultralong cycle life (e.g., 93% capacity retention over 1000 cycles at 200 mA g-1 ) and outstanding low-temperature performance. Working mechanism analyses reveal that the plateau region is the rate-determining step for HCP with a lower electrochemical reaction kinetics, which can be significantly improved in ether electrolyte.

Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination.

Abstract: Low-cost solution-based synthesis of metal halide perovskites (MHPs) invariably introduces defects in the system, which could form Shockley-Read-Hall (SRH) electron-hole recombination centers detrimental to solar conversion efficiency. Here, we investigate the nonradiative recombination processes due to native point defects in methylammonium lead halide (MAPbI3) perovskites using ab initio nonadiabatic molecular dynamics within surface-hopping framework. Regardless of whether the defects introduce a shallow or deep band state, we find that charge recombination in MAPbI3 is not enhanced, contrary to predictions from SRH theory. We demonstrate that this strong tolerance against defects, and hence the breakdown of SRH, arises because the photogenerated carriers are only coupled with low-frequency phonons and electron and hole states overlap weakly. Both factors appreciably decrease the nonadiabatic coupling. We argue that the soft nature of the inorganic lattice with small bulk modulus is key for defect tolerance, and hence, the findings are general to other MHPs.

High-Mass-Loading Electrodes for Advanced Secondary Batteries and Supercapacitors

Abstract: The growing demand for advanced electrochemical energy storage systems (EESSs) with high energy densities for electric vehicles and portable electronics is driving the electrode revolution, in which the development of high-mass-loading electrodes (HMLEs) is a promising route to improve the energy density of batteries packed in limited spaces through the optimal enlargement of active material loading ratios and reduction of inactive component ratios in overall cell devices However, HMLEs face significant challenges including inferior charge kinetics, poor electrode structural stability, and complex and expensive production processes Based on this, this review will provide a comprehensive summary of HMLEs, beginning with a basic presentation of factors influencing HMLE electrochemical properties, the understanding of which can guide optimal HMLE designs Rational strategies to improve the electrochemical performance of HMLEs accompanied by corresponding advantages and bottlenecks are subsequently discussed in terms of various factors ranging from inactive component modification to active material design to structural engineering at the electrode scale This review will also present the recent progress and approaches of HMLEs applied in various EESSs, including advanced secondary batteries (lithium-/sodium-/potassium-/aluminum-/calcium-ion batteries, lithium metal anodes, lithium-sulfur batteries, lithium-air batteries, zinc batteries, magnesium batteries) and supercapacitors Finally, this review will examine the challenges and prospects of HMLE commercialization with a focus on thermal safety, performance evaluation, advanced characterization, and production cost assessment to guide future development