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1.
To alleviate the greenhouse effect and maintain the sustainable development, it is of great significance to find an efficient and low-cost catalyst to reduce carbon dioxide (CO 2) and generate formic acid (FA). In this work, based on the first-principles calculation, the catalytic performance of a single transition metal (TM) (TM = Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, Au, or Hg) atom anchored on C 9N 4 monolayer (TM@C 9N 4) for the hydrogenation of CO 2 to FA is calculated. The results show that single TM atom doping in C 9N 4 can form a stable TM@C 9N 4 structure, and Cu@C 9N 4 and Co@C 9N 4 show better catalytic performance in the process of CO 2 hydrogenation to FA (the corresponding maximum energy barriers are 0.41 eV and 0.43 eV, respectively). The partial density of states (PDOS), projected crystal orbital Hamilton population (pCOHP), difference charge density analysis and Bader charge analysis demonstrate that the TM atom plays an important role in the reaction. The strong interaction between the 3d orbitals of the TM atom and the non-bonding orbitals (1 πg) of CO 2 allows the reaction to proceed under mild conditions. In general, our results show that Cu@C 9N 4 and Co@C 9N 4 are a promising single-atom catalyst and can be used as the non-precious metals electrocatalyst for CO 2 hydrogenation to formic acid. 相似文献
2.
In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C 3N 4 nanosheet (labeled C 3N 4– TM–O, TM= Sc–Mn). The results suggest that the TM–O binds to g-C 3N 4 nanosheets strongly for all systems. We found that the 2D C 3N 4–TM–O framework is ferromagnetic for TM= Sc, Ti, V, Cr, while it is antiferromagnetic for TM= Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures ( Tc) of the C 3N 4–TM–O (TM= Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C 3N 4 nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C 3N 4 nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride. 相似文献
3.
Water electrolysis is to split water into hydrogen and oxygen using electricity as the driving force. To obtain low-cost hydrogen in a large scale, it is critical to develop electrocatalysts based on earth abundant elements with a high efficiency. This computational work started with Cobalt on CoTa 2O 6 surface as the active site, CoTa 2O 6/Graphene heterojunctions have been explored as potential oxygen evolution reaction (OER) catalysts through density functional theory (DFT). We demonstrated that the electron transfer ( δ) from CoTa 2O 6 to graphene substrate can be utilized to boost the reactivity of Co-site, leading to an OER overpotential as low as 0.30 V when N-doped graphene is employed. Our findings offer novel design of heterojunctions as high performance OER catalysts. 相似文献
4.
结合1H NMR,13C NMR谱,分别对钨、钼配合物{WO2(C10H6O2)2(C5H11N2)2[H2N(CH2)3NH2]}3(1),{(C5H11N2)2[H2N(CH2)3NH2][MoO2(C10H6O2)2]}(2),{(C7H12N2)2[MoO2(C10H8O2)2]}(3)晶体结构中小分子环进行了归属.其中,配合物1和2中(C5H11N2)+的NMR研究证实了六元环由1,3-丙二胺和乙腈化合而成,配合物3中(C7H12N2)2+的NMR谱图证实了七元环由乙二胺和乙酰丙酮化合而成,并且推导出这些亲核加成-消除反应的反应机理.配合物1~3中的小分子环的合成在其它体系中尚未见报导,而在合成它们的反应中作为新产物随主体晶体析出,并由晶体结构解析和NMR得到了证实. 相似文献
5.
Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction(OER) performance of electrocatalysts. However, the synergistic interaction of the heteroatom and defect still needs further investigations. Herein, we demonstrated an oxygen vacancy-rich vanadium-doped Co_3O_4(V–O_v–Co_3O_4), fabricated by V-ion implantation, could be used for high-efficient OER catalysis. X-ray photoelectron spectra(XPS) and density functional theory(DFT) calculations show that the charge density of Co atom increased, and the reaction barrier of reaction pathway from O*to HOO*decreased. V–O_v–Co_3O_4 catalyst shows a low overpotential of 329 mV to maintain current density of 10 m A·cm~(-2), and a small Tafel slope of 74.5 m V·dec~(-1). This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts. 相似文献
6.
基于密度泛函理论的第一性原理方法,本文计算了单层2H相MoSe 2纳米材料表面及两种边缘(Mo原子边缘、Se原子边缘)不同活性位点、不同氢原子吸附率下的氢吸附吉布斯自由能(Gibbs free energy,用△G H0表示),并且将对应的微观结构进行了系统分析比较,得出△G H0最接近于0 eV的吸附位点及相应的吸附率.同时,结合差分电荷密度和电负性理论,分析了单层MoSe 2两种边缘氢吸附的电荷转移及成键特性,进一步解释了不同吸附位点呈现的结构与能量趋势.最后,通过基于密度泛函理论的第一性原理分子动力学模拟,研究了高温热运动对两种边缘氢吸附的影响,获得了氢原子发生脱附的临界温度及对应的微观动态过程.该理论研究从原子尺度揭示了单层2H相MoSe 2纳米材料边缘不同位点在不同温度下对氢原子吸附和脱附的微观机理,证实了Mo原子边缘的畸变和重构行为,加深了对实验中单层2H相MoSe 2边缘在不同温度下氢吸附机理的理解,为实验中通过控制MoSe 2边缘设计廉价高效的析氢催化剂提供理论参考. 相似文献
7.
Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, a composite material consisting of TC@WO 3@g‐C 3N 4@Ni‐NiO complex matrix as a bifunctional electrocatalyst for the OER and HER is described. Though the catalyst has modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER and is further improved by g‐C 3N 4. The catalytic activity arises from the synergetic effects between WO 3, Ni‐NiO, and g‐C 3N 4. A Ni‐NiO alloy and WO 3 nanoparticles decorated on the g‐C 3N 4 surface supported toray carbon (TC) matrix (TC@WO 3@g‐C 3N 4@Ni‐NiO) by a facile route that show an excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium are developed. This carbon nitride with binary metal/metal‐oxide matrix supported with TC exhibit an overpotential of 0.385 and 0.535 V versus RHE at a current density of 10 mA cm ?2 (Tafel slopes of 0.057 and 0.246 V dec ?1 for OER and HER, respectively), in 0.1 m NaOH . The catalyst is tested in water electrolysis for 17 h. 相似文献
8.
The electronic structure, magnetic and half-metal properties of inorganic-organic hybrid compound [C 4N 2H 12][Fe 4Ⅲ(HPO 3) 2(C 2O 4) 3] are investigated by using the full-potential linearized augmented plane wave (FPLAPW) method within density-functional theory (DFT) calculations. The density of states (DOS), the total energy of the cell and the spontaneous magnetic moment of [C 4N 2H 12][Fe 4Ⅱ(HPO 3) 2(C 2O 4) 3] are calculated. The calculation results reveal that the low-temperature phase of [C 4N 2H 12][Fe 4Ⅲ(HPO 3) 2(C 2O 4) 3] exhibits a stable ferromagnetic (FM) ground state, and we find that this organic compound is a half-metal in FM state. In addition, we have calculated antiferromagnetically coupled interactions, revealing the existence of antiferromagnetic (AFM), which is in agreement with the experiment. We have also found that [C 4N 2H 12][Fe 4Ⅲ(HPO 3) 2(C 2O 4) 3] is a semiconductor in the AFM state with a band gap of about 0.40 eV. Subsequently, the transport properties for potential thermoelectric applications have been studied in detail based on the Boltzmann transport theory. 相似文献
9.
Electrochemical splitting of water is an efficient way to produce clean energy for energy storage and conversion devices. Herein, 3D hierarchical NiCo 2O 4@NiO@Ni core/shell nanocone arrays (NAs) are reported on Ni foam for stable overall water splitting with high efficiency. The architecture and composition of the 3D catalysts are particularly tuned. The outstanding structural and component features of the as‐prepared 3D catalysts are characterized by the vertically grown NiCo 2O 4 nanocone/NiO nanosheet core/shell structure and Ni decorated 3D‐conductive networks, which largely prompt the catalytic performance. The hybrid catalyst with core/shell nanocone array structures exhibits superior bifuncational activities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with an overpotential of 240 and 120 mV at a current density of 10 mA cm ?2, respectively. The Tafel slope of the optimal 3D electrode is about 43 and 58 mV dec ?1 in an alkaline electrolyte for OER and HER, respectively. An alkaline electrolyzer constructed by two symmetric NiCo 2O 4@NiO@Ni electrodes delivers splendid activity toward overall water splitting with a current of 10 mA cm ?2 at only ≈1.60 V and almost no deactivation after 10 h. This work provides a promising strategy to design ternary core/shell electrodes as high performance Janus catalysts for overall water splitting. 相似文献
10.
The development of highly active and cost‐effective catalyst materials toward electrochemical water splitting is of great importance for converting and storing the intermittent solar energy in the form of hydrogen. Herein, for the first time, an ultrathin Fe and N‐co‐doped carbon nanosheet encapsulated Fe‐doped CoNi alloy nanoparticle (FeCoNi@FeNC) composite is obtained and applied as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This catalyst exhibits prominent catalytic performances for both HER and OER, which only requires overpotentials of 102 and 330 mV, respectively, to reach a current density of 10 mA cm ?2 in alkaline media. The high catalytic activity is intrinsically associated with the presence of Fe in both nanosheets and nanoparticles, which has triggered the occurrence of coordinative effects between Fe‐N‐C and FeCoNi that are beneficial for HER and OER, as revealed by electrochemical techniques. In an overall water splitting electrolyzer, FeCoNi@FeNC is employed as both the cathode and anode catalysts, achieving 12 mA cm ?2 at 1.63 V for a duration of more than 12 h. 相似文献
11.
利用密度泛函和含时密度泛函理论研究了氧(O)和硫(S)原子掺杂的石墨相氮化碳(g-C_3N_4)_6量子点的几何、电子结构和紫外-可见光吸收性质.结果表明:掺杂后(g-C_3N_4)_6量子点杂质原子周围的C-N键长发生了一定的改变,最高电子占据分子轨道-最低电子未占据分子轨道(HOMO-LUMO)能隙显著减小.形成能的计算表明O原子取代掺杂的(g-C_3N_4)_6量子点体系更稳定,且O原子更易取代N3位点,而S原子更易取代N8位点.模拟的紫外-可见电子吸收光谱表明,O和S原子的掺杂改善了(g-C_3N_4)_6量子点的光吸收,使其吸收范围覆盖了整个可见光区域,甚至扩展到了红外区.而且适当的杂质浓度使(g-C_3N_4)_6量子点光吸收在强度和范围上都得到明显改善.通过O和S掺杂的比较,发现二者在可见光区对(g-C_3N_4)_6量子点的光吸收有相似的影响,然而在长波长区域二者的影响有明显差异.总体而言,O掺杂要优于S掺杂对(g-C_3N_4)_6量子点光吸收的影响. 相似文献
12.
Carbon nitride thin films were deposited on Si(1 0 0) substrate by microwave plasma-enhanced chemical vapor deposition (PECVD). Hexamethylenetetramine (HMTA) was used as carbon and nitrogen source while N 2 gas was used as both nitrogen source and carrier gas. The sp 3-bonded C---N structure in HMTA was considered significantly in the precursor selection. X-ray diffraction analysis indicated that the film was a mixture of crystalline - and β-C 3N 4 as well as graphitic-C 3N 4 and β-Si 3N 4 which were not easily distinguished. Raman spectroscopy also suggested the existence of - and β-C 3N 4 in the films. X-ray photoelectron spectroscopy study indicated the presence of sp 2- and sp 3-bonded C---N structures in the films while sp 3C---N bonding structure predominated to the sp 2 C---N bonding structure in the bulk composition of the films. N was also found to be bound to Si atoms in the films. The product was, therefore, described as CN x:Si, where x depends on the film depth, with some evidences of crystalline C 3N 4 formation. 相似文献
13.
Single-layer MoSi 2N 4,a high-quality two-dimensional material,has recently been fabricated by chemical vapor deposition.Motivated by this latest experimental work,herein,we apply first principles calculations to investigate the electronic,optical,and photocatalytic properties of alkali-metal(Li,Na,and K)-adsorbed MoSi 2N 4 monolayer.The electronic structure analysis shows that pristine MoSi 2N 4 monolayer exhibits an indirect bandgap(E g=1.89 eV).By contrast,the bandgaps of one Li-,Na-,and K-adsorbed MoSi 2N 4 monolayer are 1.73 eV,1.61 eV,and 1.75 eV,respectively.Moreover,the work function of MoSi 2N 4 monolayer(4.80 eV)is significantly reduced after the adsorption of alkali metal atoms.The work functions of one Li-,Na-,and K-adsorbed MoSi 2N 4 monolayer are 1.50 eV,1.43 eV,and 2.03 eV,respectively.Then,optical investigations indicate that alkali metal adsorption processes substantially increase the visible light absorption range and coefficient of MoSi 2N 4 monolayer.Furthermore,based on redox potential variations after alkali metals are adsorbed,Li-and Na-adsorbed MoSi 2N 4 monolayers are more suitable for the water splitting photocatalytic process,and the Li-adsorbed case shows the highest potential application for CO 2 reduction.In conclusion,alkali-metal-adsorbed MoSi 2N 4 monolayer exhibits promising applications as novel optoelectronic devices and photocatalytic materials due to its unique physical and chemical properties. 相似文献
14.
为了寻找具有优异力学性能的新型超高温陶瓷材料, 结合进化算法和第一性原理, 系统研究了Hf-N二元体系所有稳定存在的化合物及其晶体结构. 除了实验已知的岩盐结构的HfN之外, 本文还找到了Hf 6N(R-3), Hf 3N(P6 322), Hf 3N 2(R-3m), Hf 5N 6(C2/m)和Hf 3N 4(C2/m)五种新结构, 基于准简谐近似原理计算了这些稳定结构的声子谱以验证其动力学稳定性, 常温甚至更高温度下的吉布斯自由能以验证其高温热力学稳定性. 结果表明, 这些结构是动力学稳定的, 且在1500 K以下都是热力学稳定的. 同时, 本文还列出了在搜索过程中出现的空间对称性较高、能量较低的亚稳态结构, 包括Hf 2N(P4 2/mnm), Hf 4N 3(C2/m), Hf 6N 5(C2/m), Hf 4N 5(I4/m), Hf 3N 4(I-43d)和Hf 3N 4(Pnma). 之后计算了上述所有结构的力学性质(弹性常数、体模量、 剪切模量、 杨氏模量、硬度), 随着N 所占比例的增加, 硬度呈现的整体趋势是先增大后下降, 在Hf 5N 6处取得最大值, 为21 GPa. 其中Hf 3N 2和Hf 4N 5也展现出了较高的硬度, 都为19 GPa. 最后, 计算了这些结构的电子态密度和晶体轨道汉密尔顿分布, 从电子结构的角度分析了力学性能的成因. 研究结果显示, 较强的Hf-N共价键和较低的结构空位率是Hf 5N 6具有优异力学性能的主要原因. 相似文献
15.
Reducing the Schottky barrier height (SBH) and even achieving the transition from Schottky contacts to Ohmic contacts are key challenges of achieving high energy efficiency and high-performance power devices. In this paper, the modulation effects of biaxial strain on the electronic properties and Schottky barrier of MoSi 2N 4 (MSN)/graphene and WSi 2N 4 (WSN)/graphene heterojunctions are examined by using first principles calculations. After the construction of heterojunctions, the electronic structures of MSN, WSN, and graphene are well preserved. Herein, we show that by applying suitable external strain to a heterojunction stacked by MSN or WSN — an emerging two-dimensional (2D) semiconductor family with excellent mechanical properties — and graphene, the heterojunction can be transformed from Schottky p-type contacts into n-type contacts, even highly efficient Ohmic contacts, making it of critical importance to unleash the tremendous potentials of graphene-based van der Waals (vdW) heterojunctions. Not only are these findings invaluable for designing high-performance graphene-based electronic devices, but also they provide an effective route to realizing dynamic switching either between n-type and p-type Schottky contacts, or between Schottky contacts and Ohmic contacts. 相似文献
16.
Single-atom photocatalysts, due to their high catalysis activity, selectivity and stability, become a hotspot in the field of photocatalysis. Graphitic carbon nitride (g-C 3N 4) is known as both a good support for single atoms and a star photocatalyst. Developing g-C 3N 4-based single-atom photocatalysts exhibits great potential in improving the photocatalytic performance. In this review, we summarize the recent progress in g-C 3N 4-based single-atom photocatalysts, mainly including preparation strategies, characterizations, and their photocatalytic applications. The significant roles of single atoms and catalysis mechanism in g-C 3N 4-based single-atom photocatalysts are analyzed. At last, the challenges and perspectives for exploring high-efficient g-C 3N 4-based single-atom photocatalysts are presented. 相似文献
17.
Heterojunction structure has been extensively employed for the design of novel catalysts. In the present study, density functional theory was utilized to investigate the electronic structure and hydrogen evolution performance of Ti 3C 2O 2 MXene quantum dots/graphene (QDs/G) heterostructure. Results show that a slight distortion can be observed in graphene after hybriding with QDs, due to which the electronic structure of QDs have been changed. Associated with such QDs-graphene interaction, the catalytic activity of Ti 3C 2O 2 QDs has been optimized, leading to excellent HER catalytic performance. 相似文献
18.
采用巨正则蒙特卡洛方法研究C 2H 6, CO 2和CH 4三种气体在两种沸石类咪唑骨架材料 (ZIF)-ZIF-2和ZIF-71中的吸附与分离性能. 考察了C 2H 6, CO 2和CH 4三种气体在ZIF-2和ZIF-71中的单组分吸附等温线、吸附热; C 2H 6-CH 4, CO 2-CH 4 与C 2H 6-CO 2等摩尔二元混合物的分离; 以及C 2H 6-CO 2-CH 4三元体系的分离性能. 研究结果表明: 低压下不同气体的吸附量大小与其吸附热关系紧密; 而高压下因有限的孔空间, 尺寸较小的气体分子吸附量增长趋向更快; 多组分吸附分离中, 低压下能量效应通常占据主导, ZIF优先吸附作用力较强的组分; 高压下堆积效应影响显著, ZIF会优先吸附尺寸较小的组分. ZIF-2和ZIF-71对这3种二元体系的分离性能良好. 对于三元混合物吸附分离, 在常温下3000-4000kPa范围内, ZIF-2具有良好的天然气净化性能, 可有效地分离出天然气中的C 2H 6和CO 2.
关键词:
巨正则蒙特卡洛模拟
天然气分离
沸石类咪唑骨架 相似文献
19.
The influence of pre-dosed oxygen on NO–C 2H 4 interactions on the surface of stepped Pt(3 3 2) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(3 3 2), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350 K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx. C2H4 molecules which are post-dosed at 250 K to adlayers consisting of 18O and NO do not have strong interactions with either the NO or the 18O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N2 production appear to be absent. However, C2H4 is oxidized to C18O2 by 18O atoms at higher annealing temperature. This reaction scavenges surface 18O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N2 desorption which closely resembles that following only NO exposure on a clean Pt(3 3 2), both in peak intensity and desorption temperature. It is concluded that the presence of 18O2 in the selective catalytic reduction (SCR) of NO with C2H4 on the surface of Pt(3 3 2) does not play a role of activating reactants. 相似文献
20.
本文基于第一性原理计算,证明了钴插层磷烯的析氢催化活性可以显著增强.钴插层磷烯具有金属特性,电荷从钴原子向磷烯转移,增强了磷烯的催化活性.钴插层磷烯表面的氢吸附吉布斯自由能与铂(111)表面相当,与氢覆盖度无关.研究结果表明钴原子插层提供了一种有效的方法来增强磷烯的析氢反应催化活性. 相似文献
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