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MgO has broad application potential in CO2capture at intermedium temperatures. In this paper, the effects of NaNO3doping on the properties of MgO prepared by using waste bischofite as the raw material were investigated to improve the performance of the CO2capture. MgO-doped NaNO3exhibited excellent CO2capture performance at 320 °C with a maximum adsorption capacity of 36.62 wt %. MgO-doped NaNO3has good cycling stability after 10 adsorption–desorption cycle experiments. In addition, CO2adsorption on pure MgO and MgO–NaNO3surfaces was investigated in accordance with density functional theory. Calculation results show that doping with NaNO3allows more electrons to be transferred from the MgO substrate to the CO2molecule. MgO-doped NaNO3can lead to an increase in adsorption energy, resulting in a more stable structure after adsorption and thereby promoting adsorption. The result of this study provides an effective method for the comprehensive utilization of salt lake resources.

The corrosion behavior of GH3535 alloys in KCl–MgCl2eutectic salts with or without magnesium (Mg) was investigated using the static immersion tests. The effect of purification treatment on the corrosion of GH3535 specimens was also evaluated by the different analysis. The KCl–MgCl2salts purified with Mg and reducing service temperature can slow down the corrosion rate of GH3535 specimens. Infrared spectra results showed that purification treatment reduced the content of crystal water in the KCl–MgCl2salts. The difference of hydrate content in KCl–MgCl2salts and the diffusion rate of Cr in alloy are the main reasons for the change of GH3535 specimens corrosion rate.

In this paper, the effect of thermal-induced phase transformation in Inconel 625 alloy on corrosion behavior in high-temperature molten NaCl-KCl-MgCl2salt was investigated. The results showed that the corrosion behavior was effectively influenced by the redistribution of Cr induced by the thermal-induced phase transformation. The Cr-rich chain carbides at the grain boundary and the Cr-rich regions between the needle-like δ phases formed the continuous Cr-rich channels from the grain boundary to the grain interior, which aggravated the inhomogeneous distribution of Cr and promoted the corrosion process. On this basis, the corrosion process occurred with the selective dissolution of the Cr element and invasion of Mg and O, which led to surface corrosion products composed of MgO/MgCr2O4and subsurface corrosion holes. The research results of this paper are useful for understanding the role of phase transformation in superalloys during high-temperature molten salt corrosion.

Corrosion behavior of GH3539 alloys in molten NaCl-KCl-CaCl2salts was investigated through immersion test at 800 °C under Ar for 100 h, 300 h and 500 h. The weight loss of the corroded GH3539 alloys increased from 4.63 mg/cm2to 9.92 mg/cm2, and the corrosion depth increased from 35.28 μm to 128.40 μm as the soaking time increased from 100 h to 500 h. In the early stage of corrosion, corrosive gases were produced, resulting in the uniform corrosion holes in the GH3539 alloy matrix. The chromium oxide generated by the oxidation of Cr was unstable, which in turn transformed to stable CaCrO4. The formation of Ca oxides might potentially play a pivotal role. W could react with Cl2and O2at such high temperature. The outward diffusion of W may create a pathway for the penetration of corrosive substances, thereby accelerating the corrosion of the alloy. Therefore, how to suppress the production of Cl2is the key work to depress the corrosion of GH3539 alloy in molten chloride salt. These results are instructive for the selection of alloys for the next generation of concentrated solar power.

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V2CTxthrough molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V2CTxthrough a substitution reaction during the dissolution of Li2S in LiCl–KCl molten salts. Then, surface V2O5was obtained through the in situ electrochemical charging/discharging of the S-doped V2CTx(MS-S-V2CTx) cathode. The assembled Zn/MS-S-V2CTxbattery showed a high reversible discharge capacity of 411.3 mAh g–1at a current density of 0.5 A g–1, an 80% capacitance retention after long cycle stability tests at 10 A g–1for 3000 cycles, and a high energy density of 375.5 Wh kg–1in 2M ZnSO4. Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn2+ions and improved the stability of V2O5. This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.

Molten salt-doped MgO adsorbent is considered one of the most promising CO2adsorbents in the field. In this work, MgO-based adsorbents were prepared by one-step calcination using MgCl2·6 H2O as magnesium source. The CO2adsorption performance of MgO-based adsorbents was investigated via different methods. Results showed that the maximum CO2adsorption capacity of MgO doped by LiNO3-NaNO3-KNO3was 57.1% at the CO2concentration of 80% and 350 ℃, and the MgO-based adsorbents showed good regeneration. The nanosheet structure of the MgO-based adsorbents decreased with the increase in the number of cycles, whereas the crystal structures of MgO and alkali metal nitrates did not change because of multiple decarbonization. DFT computation revealed selective adsorption of CO2on different crystal faces of MgO. The (200) crystal face of molten salt-doped MgO did not have CO2trap ability. In addition, the doped nitrate did not directly participate in the reaction but reduced the adsorption energy of MgO carbonation. The adsorption energies of the MgO (220) and (222) crystal faces after doping with nitrate were reduced to − 2.07 and − 3.26 eV, respectively. The overall energy level of adsorption decreased as the number of resonance peaks and the stability of the structure increased. This study explains why MgO currently fails to reach the theoretical adsorption capacity and reveals the underlying mechanism of molten salts.

Irradiation-induced damage of binderless nanoporous-isotropic graphite (NPIG) prepared by isostatic pressing of mesophase carbon microspheres for molten salt reactor was investigated by 3.0 MeV He+irradiation at room temperature and high temperature of 600 °C, and IG-110 was used as the comparation. SEM, TEM, X-ray diffraction and Raman spectrum are used to characterize the irradiation effect and the influence of temperature on graphite radiation damage. After irradiation at room temperature, the surface morphology is rougher, the increase of defect clusters makes atom flour bend, the layer spacing increases, and the catalytic graphitization phenomenon of NPIG is observed. However, the density of defects in high temperature environment decreases and other changes are not obvious. Mechanical properties also change due to changes in defects. In addition, SEM and Raman spectra of the cross section show that cracks appear in the depth range of the maximum irradiation dose, and the defect density increases with the increase of irradiation dose.

Intermediate temperature NaCl–AlCl3-based Al-ion batteries are considered as a promising stationary energy storage system due to their low cost, high safety, etc. However, such a cheap electrolyte has a critical feature, i.e., strong corrosion, which results in the short cycle life of the conventional Al-metal anode and also limits the development of the NaCl–AlCl3-based Al-ion batteries. A noncorrosive electrolyte may be a good choice for addressing the above challenge, while it is difficult to obtain the electrolyte that has advantages of both noncorrosion and low cost. Therefore, here, we report a Ga-metal anode in the affordable NaCl–AlCl3electrolyte for constructing a long-life stationary Al-ion energy storage system. This featured liquid metal anode shows good alloying and dealloying processes between metallic Ga and Al, as well as renders superior stability of the interface between the electrolyte and the anode (e.g., smoothly running for over 580 h at 2 mA cm–2). No-corrosion and no-pulverization problems appear in this novel liquid/liquid interface. Those advantages demonstrate that the liquid Ga-metal anode has a great promise for the improvement of the NaCl–AlCl3-based Al-ion batteries for large-scale stationary energy storage applications.

Molten MgCl2-based chlorides have emerged as potential thermal storage and heat transfer materials due to high thermal stabilities and lower costs. In this work, deep potential molecular dynamics (DPMD) simulations by a method combination of the first principle, classical molecular dynamics, and machine learning are performed to systemically study the relationships of structures and thermophysical properties of molten MgCl2–NaCl (MN) and MgCl2–KCl (MK) eutectic salts at the temperature range of 800–1000 K. The densities, radial distribution functions, coordination numbers, potential mean forces, specific heat capacities, viscosities, and thermal conductivities of these two chlorides are successfully reproduced under extended temperatures by DPMD with a larger size (5.2 nm) and longer timescale (5 ns). It is concluded that the higher specific heat capacity of molten MK is originated from the strong potential mean force of Mg–Cl bonds, whereas the molten MN performs better in heat transfer due to the larger thermal conductivity and lower viscosity, attributed to the weak interaction between Mg and Cl ions. Innovatively, the plausibility and reliability of microscopic structures and macroscopic properties for molten MN and MK verify the extensibilities of these two deep potentials in temperatures, and these DPMD results also provide detailed technical parameters to the simulations of other formulated MN and MK salts.

The NaNO3-KNO3salt has the disadvantage of poor heat transfer capacity and low heat transfer efficiency in single-tank heat storage systems. However, molten salt can be used as phase change materials (PCM) and encapsulated with highly conductive sphere-shaped metals as PCM spheres. Arranging these spheres can appropriately change the situation. In this study, a heat storage system of a multilayer packed bed of PCM spheres consisting of NaNO3-KNO3salt and type 316 stainless steel sphere shell was designed. This system's heat transfer and heat storage performance were also investigated using CFD simulation. For the same sphere diameter, the heat storage efficiency of hexagonal close packing (HCP) was 1.1 times that of cubic close packing (CCP). With the same porosity, the heat charging efficiency for the case using the 47.5 mm sphere diameter was the highest, at 99.3 %. When the number of layers of spheres was increased from 3 to 7, the heat flux through the sphere wall and the heat storage density of PCM spheres decreased from 40.8 kW and 67.3 × 105 kJ/m3to 35.7 kW and 59.2 × 105 kJ/m3, respectively. Therefore, the heat charging efficiency of HCP was better than that of CCP. Reducing sphere size could shorten the heat transfer time and improve the heat storage efficiency. These numerical simulation results are consistent with the commonly known fact that the volumetric heat transfer intensity in the porous media is proportional to the reciprocal particle size since the smaller the particle size, the larger the contact area between the packing and the fluid. The conclusion drawn from the present findings provides an idea for designing a PCM heat storage system with high temperature and high efficiency of molten salt. The idea could also be used as a reference for the optimal design of a packed bed reactor.

High temperature corrosion behaviors of 321 stainless steel (321SS) in purified NaCl-MgCl2eutectic salts were investigated by static corrosion test at 500, 600 and 700 °C for 240 h in Ar. The corrosion rate of 321SS at 500 °C is approximately 60.77 μm/y, and it gradually intensifies with increasing temperatures. The corrosion rate reached 136.70 μm/y at 600 °C and 301.02 μm/y at 700 °C, respectively. As the temperature increases, the accelerated dissolution of Cr leads to intergranular corrosion, and a Fe-Ni phase appears at 600 °C due to the loss of Cr. Obvious intergranular corrosion occurs alongside the zone of Cr active dissolution at 700 °C. 321SS shows good corrosion resistance in purified NaCl-MgCl2at 500 °C. However, the corrosion resistance gradually deteriorates when the temperature exceeds 600 °C. Further, molten salt purification and corrosion control are effective methods to solve high temperature corrosion problems. The results provide basis data for the usage of 321SS in NaCl-MgCl2salt at high temperature.

Yttrium-doped barium zirconate (BZY) has emerged as an attractive candidate of oxygen ion (O2–) conducting solid electrolyte because of its high ionic conductivity and excellent chemical stability. In this work, the O2–transport properties and mechanisms of BZY coexisting oxygen vacancies, dopants, and edge dislocations are simulated by reactive molecular dynamics for the first time, and the yttrium concentration (Y%) and temperature (T) dependences of thermodynamic and kinetic properties are studied for the bulk and dislocation (Bulk and Disl) systems, respectively. It is concluded that the Y% under 20 mol % for Bulk BZY can promote O2–conduction, while 30 mol % Y-doped Disl BZY has the highest O2–diffusion coefficient. Besides, dislocations will accelerate O2–diffusion when Tis less than 1173.15 K due to the formation of double-bottle diffusion channels that enables facile reorientation of oxygen polyhedron. Therefore, it is feasible to introduce line defects to enhance ion conductivity at low temperature in the practical applications of BZY electrolytes.

Two kinds of NaCl-KCl-FeCl3eutectic salts were developed based on the thermodynamic calculation and experimental measurement for the low-temperature thermal energy storage. The NaCl-FeCl3and KCl-FeCl3systems were firstly carried out through the CALculation of PHAse Diagrams method, where the calculated values were in excellent agreement with the experimental data. A set of reliable thermodynamic parameter of the NaCl-KCl-FeCl3system was finally obtained. The predicted two eutectic temperature (T = 138.6 °C and T = 140.0 °C) of the NaCl-KCl-FeCl3system are in excellent agreement with the present experimental data (T = 138.2 ± 0.2 °C and T = 140.2 ± 0.3 °C). The actual eutectic points of the NaCl-KCl-FeCl3system are placed at 138.2 ± 0.2 °C &XNaCl = 0.35 mol, XKCl = 0.17 mol, and XFeCl3 = 0.48 mol and 140.2 ± 0.3 °C &XNaCl = 0.34 mol, XKCl = 0.13 mol, and XFeCl3 = 0.53 mol. The fusion enthalpies of the NaCl-KCl-FeCl3system are 70.05 ± 1.18 and 75.18 ± 1.27 J/g, respectively. The average specific heat capacities are 0.80 ± 0.02 J/g·°C and 0.90 ± 0.02 J/g·°C, separately. Their decomposition temperatures are 389.4 ± 0.2 °C and 399.6 ± 0.3 °C. The weight losses are still less than 6 wt% even at 400 °C for 300 h. Two kinds of NaCl-KCl-FeCl3eutectic salts have relatively low melting temperature, good thermal stability, suitable working temperature and low cost, which can be considered as one of the promising candidate thermal energy storage materials.

A new kind of highly durable, electrically conductive UHMWPE fibers coated with copper was fabricated through a novel, simple, and universal process in this paper. Poly(acrylic acid) was anchored on the surface of UHMWPE fibers through radiation-induced graft polymerization. Then the grafted fiber adsorbed silver ions and was placed in a plated bath for electroless deposition of copper to yield conductive fibers. The result of single fiber tensile strength ascertained that the metallized fibers retained the excellent mechanical properties of original fibers. Importantly, the formation of three-dimensional network structures consisted of grafted polymer chains and metal particle deposited on the surface of UHMWPE fiber, which can effectively improve the adhesion between the copper and the fibers, providing excellent electrical stability and durability even after 30 accelerated washing cycles. Therefore, this method can be extended as a universal approach to fabricating high-performance conductive fibers or fabrics from other kinds of polymer substrates.

•LES with low melting point was chosen as the PCM for medium temperature TES.•LES/GF composites were prepared by the vacuum impregnation.•The thermal properties of the LES/GF composites were studied and obtained.•The 3D continuous network contributes to the high thermal conductivity of LES/GF.

The phase change material (PCM) spheres using 316SS as the ball shell and solar salt (NaNO3-KNO3, 60–40 wt%) as the PCM were arranged in an orderly pebble-bed arrangement. The charging performance, energy and exergy of PCM spheres in the packed ball thermal energy storage system (PBTES) were investigated using CFD simulation in order to solve the problem of heat storage at 300 °C–500 °C. The results show that the total melting time of PCM spheres slightly decreases from 1455 s to 1319 s with the inlet velocity increasing. The average heat storage efficiency of PCM spheres and PBTES are improved with the inlet temperature increasing. When the inlet flow rate increases from 0.01 m/s to 0.10 m/s, the energy efficiency of PBTES increases approximately 5.06 times, and the exergy efficiency increases from 17.91 % to 99.55 %. However the heat energy storage and exergy efficiency of PCM spheres are not affected by the inlet velocity changing. The energy efficiency of PBTES increases about 2.09 times, and the exergy efficiency increases from 30.29 % to 70.93 % with the inlet temperature grows from 300 °C to 500 °C. It provides an idea for the design of the medium-high temperature and high-efficiency molten salt PCM heat storage system.

The corrosion behaviors of 316 stainless steel (316 SS) in NaNO3-NaCl-NaF molten salt and vapor were investigated at 450 °C for 130 h under argon gas and air conditions, respectively. 316 SS suffered from weight gain under the argon gas condition yet experienced weight loss under the air condition. Fe-O enriched layer with different crystal forms (i.e., whisker-like, flake, and grain shapes) was detected by XRD. The crystal forms were relatively homogeneously distributed after the NaNO3-NaCl-NaF molten salt corrosion but were not uniform after the NaNO3-NaCl-NaF vapor corrosion. 316 SS experienced a more serious corrosion attack in salts vapor than that in NaNO3-NaCl-NaF molten salt regardless of the experimental condition. The corresponding corrosion mechanisms were also investigated, and results show that the oxides helped mitigate further corrosion attacks. These findings provide direct guidelines for choosing the appropriate molten salts and alloys for CSP.

Through meticulous design, a Li-lacking Cr2O5cathode is physically mixed with Li-rich Li1.2Ni0.13Co0.13Mn0.54O2(LNCM) cathode to form composite cathodes LNCM@xCr2O5(x= 0, 0.1, 0.2, 0.3, 0.35, 0.4, mass ratio) in order to make use of the excess lithium produced by the Li-rich component in the first charge-discharge process. The initial coulombic efficiency (ICE) of LNCM half-cell has been significantly increased from 75.5% (x= 0) to 108.9% (x= 0.35). A novel full-cell comprising LNCM@Cr2O5composite cathode and Li4Ti5O12anode has been developed. Such electrode accordance, i.e., LNCM@Cr2O5//Li4Ti5O12(“L-cell”), shows a particularly high ICE of 97.7%. The “L-cell” can transmit an outstanding reversible capacity up to 250 mA h g−1and has 94% capacity retention during 50 cycles. It also has superior rate capacities as high as 122 and 94 mA h g−1at 1.25 and 2.5 A g−1current densities, which are even better in comparison of Li-rich//graphite full-cell (“G-cell”). The high performance of “L-cell” benefiting from the well-designed coulombic efficiency accordance mechanism displays a great potential for fast charge-discharge applications in future high-energy lithium ion batteries. 本文将缺锂态的Cr2O5正极材料与Li1.2Ni0.13Co0.13Mn0.54O2(LNCM)富锂相正极材料进行物理混合, 形成了复合正极材料LNCM@xCr2O5(x= 0,0.1,0.2,0.3,0.35, 0.4), 从而在第一次充放电过程中达到有效利用富锂相所产生的不可逆的锂离子. 复合之后, LNCM半电池的首次库仑效率(ICE)得到显著提高, 从75.5(x= 0)提高到了108.9(x= 0.35). LNCM@Cr2O5复合正极材料和Li4Ti5O12负极材料匹配而成的新型锂离子全电池, 即LNCM@Cr2O5//Li4Ti5O12(L电池)表现出高达97.7的ICE. 不仅如此, L电池还表现出了高达250 mA h g—1的可逆容量, 并且 在循环50次之后仍具有94%的容量保持率. 此外, 在1.25和2.5 A g—1电流密度下, 它还具有高达122和94 mA h g—1的放电比容量, 远远优于LNCM//石墨全电池(G电池). L电池的高性能得益于精心设计的库仑效率匹配机制, 并且在未来高能量锂离子电池的快速充放电应用中表现出巨大的潜力.

The homogeneous and controllable morphology of anhydrous MgCO3particles with excellent properties is difficult to obtain because of a variety of synthetic factors. The effect of succinic acid as a crystal modifier on the particle morphology transformation of anhydrous MgCO3was investigated by the hydrothermal method. The effect of the addition of succinic acid on the particles was similar to that of temperature change. The morphology of particles with folded diamond-like shape was gradually uniform, and the particle size was between 3.3 and 7.5 μm. Anhydrous MgCO3particles prepared at pH 9 could easily agglomerate, and the average particle size increased from diamond-like to cube-like as the reaction time increased. The interaction between succinic acid and magnesium ion at different concentrations was the main factor responsible for the morphological changes. The pH, temperature, and time affected the molecular motion rate and crystal growth.

The corrosion effect of Ca(NO3)2-NaNO3-KNO3on 316 stainless steel (316SS) and nodular cast iron 600-3 (QT-600-3) at 520 °C was studied by static corrosion method in argon. After corrosion for 100 h, it was found that there were oxides on the corroded surfaces of the two alloys in XRD spectra. The oxide on the surface of 316SS alloy after corrosion was very thin, and the thickness of Cr depleted layer on the surface of corroded 316SS was only 0.4 μm. On the other hand, a loose oxide layer with a thickness of about 42 μm was formed on the surface of QT-600-3 after corrosion, and its main components were Fe2O3and Fe3O4. The corrosion of Ca(NO3)2-NaNO3-KNO3salt on QT-600-3 is much greater than that on 316SS. The fundamental reason for the different corrosion performance of the two materials was the different oxide structures formed on the surface of the two alloy materials. The results may be helpful to the selection of structural materials when Ca(NO3)2-NaNO3-KNO3salt is used as the heat storage medium.

A complete and ordered layered structure on the surface of LiNi0.815Co0.15Al0.035O2(NCA) has been achieved via a facile surface-oxidation method with Na2S2O8. The field-emission transmission electron microscopy images clearly show that preoxidation of the hydroxide precursor can eliminate the crystal defects and convert Ni(OH)2into layered ß-NiOOH, which leads to a highly ordered crystalline NCA, with its (006) planes perpendicular to the surface in the sintering process. X-ray photoelectron spectroscopy and Raman shift results demonstrate that the contents of Ni2+and Co2+ions are reduced with preoxidization on the surface of the hydroxide precursor. The level of Li+/Ni2+disordering in the modified NCA determined by the peak intensity ratio I(003)/I(104)in X-ray diffraction patterns decreases. Thanks to the complete and ordered layered structure on the surface of secondary particles, lithium ions can easily intercalate/extract in the discharging–charging process, leading to greatly improved electrochemical properties.

NaNO3-NaCl-NaF salts were investigated by thermodynamic calculation and experimental measurement. A set of self-consistent thermodynamic parameter for the NaNO3-NaCl-NaF salts was finally obtained, by which the predicted melting point (i.e., 288.2 °C) is in excellent agreement with the experimental value (i.e., 288.0 °C). The actual eutectic point of the NaNO3-NaCl-NaF salts is placed at 288.0 °C and XNaNO3 = 0.905 mol, XNaCl = 0.059 mol, and XNaF = 0.036 mol. The fusion enthalpy of the NaNO3-NaCl-NaF salts is 210.0 J/g, and the average liquidus specific heat capacity is 1.760 ± 0.030 J/g·°C. Weight loss is only 5.0 wt% at 650 °C, and its thermal stability is high. The fusion enthalpy is increased by 86.7% than that of NaNO3-KNO3and 252.0% than that of NaNO3-NaNO2-KNO3. Furthermore, the cost of storage solid-liquid phase change heat of the NaNO3-NaCl-NaF salts is only 50% of that of NaNO3-KNO3salt and 25% of that of NaNO3-NaNO2-KNO3salts. The developed NaNO3-NaCl-NaF eutectic salts has relatively superior thermophysical properties, suitable working temperature and good economy performance, and can be used as one of the candidate thermal energy storage fluids. This work provides fundamental reference for the selection of thermal energy storage materials and enriches molten salts databases.

Confinement can induce unusual behavior in the properties of matter. Using atomistic molecular dynamics simulations, we report here a liquid-to-solid transition of a bilayer of ionic liquid 1,3-dimethylimidazolium chloride ([Dmim][Cl]) confined between graphite walls in order to mimic the phase transition of an ionic liquid confined to hydrophobic nanospace. It was found that the ionic liquid bilayer undergoes a clear and drastic phase transition at a wall distance of about 1.1 nm, forming a new high-melting-point solid phase with different hydrogen bonding networks. In the new phase, each cation is surrounded by the three nearest-neighbor anions, and each anion is also encircled by the three nearest-neighbor cations. Strong π−π stacking interactions are found between the cations of the bilayer solid. The anions can be formed into a hexagonal ring around the cations. The new bilayer solid is a high-melting-point crystal possessing a melting point of 825−850 K, which is higher than that of the bulk crystal by more than 400 K.

•The latent heat of novel NaF-KCl reciprocal salt is up to 454.8 J/g.•Key thermophysical properties of NaF-KCl were first experimental determined.•Physical property prediction method of reciprocal salts were systematic evaluated.•Cost of per kJ energy of NaF-KCl was 7%-68% lower than that of established molten salts.

•Zirconate-silicate hybrids were prepared as high temperature CO2capture sorbent.•CO2adsorption/desorption dynamics of hybrid were studied by the different methods.•Si-OH groups diffuse into alkali and condensate to form SiOSi bonds in interphase.•The electron-donating ability determines chemical structure and CO2storage capacity.

Preterm birth is the leading cause of neonatal deaths and is also associated with well-known infant morbidities. Although the effects of active smoking during pregnancy are recognized, evidence for the effects of passive smoking is mixed. In China, 3.2 of women and 48.9 of men are active smokers, which offers a unique opportunity for studying passive smoking and reproductive health in nonsmoking women. This cohort study was undertaken to examine the association between passive smoking and preterm birth by clinical subtypes.