In Situ Formation of Polycyclic Aromatic Hydrocarbons as an Artificial Hybrid Layer for Lithium Metal Anodes.

Nonuniform Li deposition causes dendrites and low Coulombic efficiency (CE), seriously hindering the practical applications of Li metal. Herein, we developed an artificial solid-state interphase (SEI) with planar polycyclic aromatic hydrocarbons (PAHs) on the surface of Li metal anodes by a facile in situ formation technology. The resultant dihydroxyviolanthron (DHV) layers serve as the protective layer to stabilize the SEI. In addition, the oxygen-containing functional groups in the soft and conformal SEI film can regulate the diffusion and transport of Li ions to homogenize the deposition of Li metal. The artificial SEI significantly improves the CEs and shows superior cyclability of over 1000 h at 4 mAh cm-2. The LiFePO4/Li cell (2.8 mAh cm-2) enables a long cyclability for 300 cycles and high CEs of 99.8%. This work offers a new strategy to inhibit Li dendrite growth and enlightens the design on stable SEI for metal anodes.

Cu2O/SrTi1-xCrxO3 Heterojunction Photocatalyst for the Efficient Degradation of Isopropanol under Visible Light Irradiation.

A heterojunction of Cu2O and Cr-doped SrTiO3 (SrTi1-xCrxO3) was designed for selective photocatalytic isopropanol (IPA) oxidation under visible light irradiation. The photocatalytic oxidation of IPA was measured in a fixed-bed reactor. Cr dopants can increase the light absorption and improve the activity of the catalyst. The formation of the Cu2O/SrTi1-xCrxO3 heterojunction can further broaden the absorption range of lights and dramatically increase the photocatalytic activity for selective oxidation of IPA. The 3% Cu2O/SrTi0.99Cr0.01O3 catalyst can fully convert ∼1000 ppm IPA under illumination in 2 h. The selectivity of acetone is ∼100%. The yield is 83 and 4 times higher than that using SrTiO3 and SrTi0.99Cr0.01O3 as catalysts, respectively. By measuring the ultraviolet-visible absorption spectra and Mott-Schottky plots, we obtained the band structure of the heterojunction, which shows that the conduction and valence bands of Cu2O are higher than those of SrTi1-xCrxO3, therefore facilitating the separation and transfer of photogenerated electrons and holes. In addition, electron paramagnetic resonance spectroscopy and radical trapping tests reveal that the generation of hydroxyl and superoxide leads to photocatalytic oxidation of IPA by the heterojunction photocatalyst.

Boron-Doped Dinickel Phosphide to Enhance Polysulfide Conversion and Suppress Shuttling in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are promising for next-generation high-energy energy storage systems. However, the slow reaction kinetics render mobile polysulfides hardly controlled, yielding shuttling effects and eventually damaging Li metal anodes. To improve the cyclability of Li-S batteries, high-efficiency catalysts are desired to accelerate polysulfide conversion and suppress the shuttling effect. Herein, we studied a doping system with Ni2P and Ni2B as the end members and found a B-doped Ni2P catalyst that demonstrates high activity for Li-S batteries. As anionic dopants, B demonstrates an interesting reverse electron transfer to P and tunes the electronic structure of Ni2P dramatically. The resultant B-doped Ni2P exhibits short Ni-B bonds and strong Ni-S interaction, and the electron donation of B to P further enhances the adsorption of polysulfide on catalysts. The S-S bonds of polysulfides were activated appropriately, therefore decreasing a low energy barrier for conversion reactions.

Gas-phase synthesis of Ti2CCl2 enables an efficient catalyst for lithium-sulfur batteries.

MXenes have aroused intensive enthusiasm because of their exotic properties and promising applications. However, to date, they are usually synthesized by etching technologies. Developing synthetic technologies provides more opportunities for innovation and may extend unexplored applications. Here, we report a bottom-up gas-phase synthesis of Cl-terminated MXene (Ti2CCl2). The gas-phase synthesis endows Ti2CCl2 with unique surface chemistry, high phase purity, and excellent metallic conductivity, which can be used to accelerate polysulfide conversion kinetics and dramatically prolong the cyclability of Li-S batteries. In-depth mechanistic analysis deciphers the origin of the formation of Ti2CCl2 and offers a paradigm for tuning MXene chemical vapor deposition. In brief, the gas-phase synthesis transforms the synthesis of MXenes and unlocks the hardly achieved potentials of MXenes.

CrP Nanocatalyst within Porous MOF Architecture to Accelerate Polysulfide Conversion in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries demonstrate great potential for next-generation electrochemical energy storage systems because of their high specific energy and low-cost materials. However, the shuttling behavior and slow kinetics of intermediate polysulfide (PS) conversion pose a major obstacle to the practical application of Li-S batteries. Herein, CrP within a porous nanopolyhedron architecture derived from a metal-organic framework (CrP@MOF) is developed as a highly efficient nanocatalyst and S host to address these issues. Theoretical and experimental analyses demonstrate that CrP@MOF has a remarkable binding strength to trap soluble PS species. In addition, CrP@MOF shows abundant active sites to catalyze the PS conversion, accelerate Li-ion diffusion, and induce the precipitation/decomposition of Li2S. As a result, the CrP@MOF-containing Li-S batteries demonstrate over 67% capacity retention over 1000 cycles at 1 C, ∼100% Coulombic efficiency, and high rate capability (674.6 mAh g-1 at 4 C). In brief, CrP nanocatalysts accelerate the PS conversion and improve the overall performance of Li-S batteries.

Regulated Electrodeposition of Na Metal in Monolithic ZIF-Pillared Graphene Anodes.

Sodium (Na) metal batteries receive increasing attention because of their high energy densities and low costs that are enabled by the abundant Na resources. However, dendritic growth and low efficiency of Na-metal anodes limit the practical applications of Na-metal batteries. Here, we propose a three-dimensionally pillared structure in which carbonized nanoparticles of zeolite imidazolate framework-8 (ZIF-8) are sandwiched between reduced graphene oxide (rGO) sheets (ZIF-8-C@rGO). Such a pillared structure enables two advantages over rGO. First, the sodiation products of ZIF-8 (NaZn13, Na2O, and N-doped carbon) have a strong chemical affinity to Na metal, thereby inducing favorable nucleation of Na metal to guide Na deposition. Second, the pillared structure could facilitate the diffusion of Na ions through rGO sheets and help homogenize the current distribution, leading to a uniform deposition of Na metal. As a result, ZIF-8-C@rGO exhibits a dendrite-free morphology during Na plating/stripping and excellent cycling stability with high Coulombic efficiency of over 99.8% for at least 2000 h. A symmetric cell could maintain more than 4000 h with a stable average overpotential of only 30 mV at a capacity of 1 mA h cm-2. This work demonstrates that the design of a ZIF-pillared structure could combine thermodynamic and kinetic regulating factors to offer an alternative solution to the development of durable Na electrodes for high-performance Na-metal batteries.

Transferring Liquid Metal to form a Hybrid Solid Electrolyte via a Wettability-Tuning Technology for Lithium-Metal Anodes.

Integrating solid-state electrolyte (SSE) into Li-metal anodes has demonstrated great promise to unleash the high energy density of rechargeable Li-metal batteries. However, fabricating a highly cyclable SSE/Li-metal anode remains a major challenge because the densification of the SSE is usually incompatible with the reactive Li metal. Here, a liquid-metal-derived hybrid solid electrolyte (HSE) is proposed, and a facile transfer technology to construct an artificial HSE on the Li metal is reported. By tuning the wettability of the transfer substrates, electron- and ion-conductive liquid metal is sandwiched between electron-insulating and ion-conductive LiF and oxides to form the HSE. The transfer technology renders the HSE continuous, dense, and uniform. The HSE, having high ion transport, electron shut-off, and mechanical strength, makes the composite anode deliver excellent cyclability for over 4000 h at 0.5 mA cm-2 and 1 mAh cm-2 in a symmetrical cell. When pairing with LiFePO4 and sulfur cathodes, the HSE-coated Li metal dramatically enhances the performance of full cells. Therefore, this work demonstrates that tuning the interfacial wetting properties provides an alternate approach to build a robust solid electrolyte, which enables highly efficient Li-metal anodes.

[Relationship between gender, experience of migration and premarital sex among out-of-school youths in rural Hainan, China].

OBJECTIVE: To assess pre-marital sex behavior and its relationship with gender and experience of migration among 16 - 24 years-old out-of-school youths in rural Hainan province, China. METHODS: 160 eligible youths from each of the 2 townships in County A and 80 from each of the 6 townships in County B were recruited, under equal proportion on gender, age distribution and experience of migration. An interviewer-administered, standardized questionnaire was used. RESULTS: 760 eligible participants (with each gender of 380) were interviewed. There were no significant differences in the proportions of reporting as sexually active (56.8% and 57.9%) or having premarital sex (54.5% and 50.0%) between male and female youths. However, among those sexually active participants, the average age at first sexual intercourse was (18.2 ± 1.9 years or 19.2 ± 1.8 years, P < 0.01), the average age of first-time leaving hometown for work (18.0 ± 2.3 years or 16.5 ± 1.9 years P < 0.01) and the percentage of having first sexual intercourse before 18 years old (59.3% vs. 35.5%, P < 0.01) were different between males and females. 31.2% of the male youths reported that their sexual debut happened before they left their hometown for work and 45.9% of the sex debut appeared within 1 year after they left hometown. However, 78.5% of the sexually active female youths reported their sexual debut happened 1 year after leaving their hometown. Data from the multivariate analysis showed that being away from hometown for more than 3 months and having more friends who presumably had presumably pre-marital sex experiences were more likely to report pre-marital sex behavior. Older men were more likely to report pre-marital sex behavior than the younger ones. Married women were more likely to report pre-marital sex behavior than the unmarried ones. Through multivariate analysis on unmarried men, data showed that those having had experience on migration and at older age were associated with experiencing premarital sex. CONCLUSION: Gender difference was identified on the pattern of migration and its relationship with premarital sex among out-of-school rural youths in Hainan province. When prevention program is developed for rural youth, these differences should be taken into account.

Challenges, strategies, and lessons learned from a participatory community intervention study to promote female condoms among rural sex workers in Southern China.

China faces a rapidly emerging HIV epidemic and nationwide resurgence of sexually transmitted infections associated with a growing sex industry. Community empowerment and capacity building through community-based participatory research partnerships show promise for developing, testing, and refining multilevel interventions suited to the local context that are effective and appropriate to address these concerns. However, such efforts are fraught with challenges, both for community collaborators and for researchers. We have built an international team of scientists from Beijing and the United States and collaborating health policy makers, health educators, and care providers from Hainan and Guangxi Province Centers for Disease Prevention and Control and the local counties and towns where we are conducting our study. This team is in the process of testing a community-wide, multilevel intervention to promote female condoms and other HIV prevention within sex-work establishments. This article presents lessons learned from our experiences in the first two study sites of this intervention trial.

Molecular epidemiological tracing of HIV-1 outbreaks in Hainan island of southern China.

OBJECTIVES: To determine the prevalence of HIV in Hainan island and the molecular epidemiological linkages related to risk factors of viral transmission. METHODS: A governmental HIV/AIDS surveillance program, HIV serological study was conducted in volunteers from several high-risk groups between 1991 and 2006 in Hainan province. By phylogenetic reconstruction, we performed a molecular epidemiological tracing in a representative subset of the HIV-1-seropositive individuals diagnosed during this survey. RESULTS: Of 499 752 volunteers, 523 (0.1%) accumulated cases of HIV-1 infection (69.2% needle-sharing drug users, 19.3% heterosexually acquired adults, 3.3% receivers of blood transfusion, 0.8% children born from HIV-1-infected mothers, and 7.7% remained unknown) were diagnosed. Among 83 patient samples examined (70 were infected with HIV-1 subtypes CRF01_AE and eight, two, one, one, and one were B', C, CRF08_BC, B, and a new CRF01_AE/B' recombinant, respectively), 66 (79.5%) were segregated into one large cluster (59 sequences) (founder effect) and one small cluster (three sequences) of CRF01_AE, one small cluster (two sequences) of B', and one small cluster (two sequences) of C. Phylogenetic and epidemiological linkages confirmed four heterosexual transmission events and rejected two potential heterosexual transmission suggested by contact tracing. Only two cases of CRF01_AE showed mutations conferring resistance to nucleoside and nonnucleoside reverse transcriptase inhibitors. CONCLUSION: The reconstruction of current HIV-1 outbreaks by molecular epidemiological tracing is helpful for identifying epidemic sources and for defining prevention strategies.

Working to prevent HIV/STIs among women in the sex industry in a rural town of Hainan, China.

We evaluated a two-phase HIV/STIs prevention intervention for female sex workers in a resource-limited rural town in Hainan Province, China. The primary intervention strategy, conducted from 1997 to 2000, was a condom promotion campaign conducted through outreach to sex workers. Four serial cross-sectional surveys were carried out before and after the intervention. Over a period of 2 years, reported condom use during the most recent sexual encounter increased from about 50% to more than 70%; and condom use in more than 50% of sexual acts during the past 6 months increased from less than 40% to near 80% of respondents. Controlling for education, ethnicity and age, reading of educational materials (our intervention variable) was a significant contributor to a higher knowledge score, motivation to use condoms, and reported condom use. This study demonstrates that outreach to female sex workers, if appropriately tailored to local settings, can increase condom use in a resource-limited rural area.

Self-reported symptoms of reproductive tract infections among rural women in Hainan, China: prevalence rates and risk factors.

OBJECTIVES AND GOAL: The goal of this study was to examine risk of reproductive tract infections (RTIs) among women in rural China, including prevalence, influence of sociodemographic characteristics, knowledge, hygienic practices, attitudes, and behaviors related to premarital and extramarital sex, and abortion. STUDY: During 2000, a stratified cluster sample of 606 rural married women in Hainan province completed an interviewer-administered standardized questionnaire. RESULTS: Overall, 39% of participants reported at least 1 RTI symptom in their lifetime and 20% during the past 6 months. Having had premarital sex, having sex during menstruation, belonging to an ethnic minority, being knowledgeable about RTIs, and living in a village at medium economic level were all related to having RTI symptoms. CONCLUSION: Among married women in rural China, the prevalence of RTI symptoms was high, indicating the need for health education, particularly targeting women from ethnic minorities and resource-poor areas.

[A questionnaire-based survey on attitude and behavior of sex among rural women in Hainan province].

OBJECTIVE: To define the profile and risk factors of sexual attitude and behavior of rural women. METHODS: Using stratified cluster sampling, tape-recorded interviews and face to face interviews were carried out among 606 rural women. RESULTS: 24.6% of the women being studied accepted the idea of "premarital sexual intercourse" and thought "premarital sexual intercourse between a couple" acceptable accounted for 34.2%, 14.7% and 4% of the women reported having had premarital sexual intercourse and premarital induced abortion respectively. 5.0% of the women admitted having had sexual intercourse during menstruation. 4% and 3% of the women under study accepted "extramarital sexual intercourse" and "paid sexual intercourse" if they were in need of money. None of the women reported ever having had extramarital sex or paid sex. The results derived from two different methods did not differ significantly. Logistic rgression suggested that age, education and ethnicity were associated with attitude towards premarital sex, and age was associated with premarital sexual behavior. CONCLUSION: Sex education need to be promoted and targeted among rural population at early age. "Tape-recorded interview" method did not show a better validity in this study.