We developed a method to engineer well-distributed dicobalt phosphide (Co2P) nanoparticles encapsulated in N,P-doped graphene (Co2P@NPG) as electrocatalysts for hydrogen evolution reaction (HER). We ...fabricated such nanostructure by the absorption of initiator and functional monomers, including acrylamide and phytic acid on graphene oxides, followed by UV-initiated polymerization, then by adsorption of cobalt ions and finally calcination to form N,P-doped graphene structures. Our experimental results show significantly enhanced performance for such engineered nanostructures due to the synergistic effect from nanoparticles encapsulation and nitrogen and phosphorus doping on graphene structures. The obtained Co2P@NPG modified cathode exhibits small overpotentials of only −45 mV at 1 mA cm–2, respectively, with a low Tafel slope of 58 mV dec–1 and high exchange current density of 0.21 mA cm–2 in 0.5 M H2SO4. In addition, encapsulation by N,P-doped graphene effectively prevent nanoparticle from corrosion, exhibiting nearly unfading catalytic performance after 30 h testing. This versatile method also opens a door for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by graphene.
Crop straw open burning is considered as an important source of greenhouse gas and atmospheric pollutants emissions, which affects global climate change and regional air quality. However, due to the ...limitation of data availability, the current emission estimation of greenhouse gas and atmospheric pollutants from crop straw open burning remains uncertain based on the bottom-up method. Therefore, we re-estimate the greenhouse gas and atmospheric pollutants from crop straw open burning at the county level based on a national questionnaire and the up-to-data emission factors. Results showed that emissions of CO
2
, CH
4
, N
2
O, PM
10
, PM
2.5
, NMVOC, NH
3
, NOx, SO
2
, CO, BC, and OC from open straw burning are 69250.8 Gg, 242.9 Gg, 4.2 Gg, 771.0 Gg, 539.7 Gg, 498.2 Gg, 34.7 Gg, 200.4 Gg, 24.8 Gg, 3426.5 Gg, 63.0 Gg, and 278.5 Gg, respectively, which were lower than those of previous studies. Maize was the largest contribution, followed by wheat, rice. Hotspots for greenhouse gas and atmospheric pollutants from straw burning are mainly distributed in the 54 counties of northeast China, accounting for 20% of total emissions on average. However, the high emission of maize, wheat, and rice are mainly located at the counties of north China, northeast China, and middle-lower Yangtze River region, respectively. This study not only provides the targeted counties that need decrease further the straw open burning, but also improves the precision of emission estimation that benefits air quality modeling.
The proper choice of nonprecious transition metals as single atom catalysts (SACs) remains unclear for designing highly efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, ...reported is an activity correlation with catalysts, electronic structure, in order to clarify the origin of reactivity for a series of transition metals supported on nitrogen‐doped graphene as SACs for HER by a combination of density functional theory calculations and electrochemical measurements. Only few of the transition metals (e.g., Co, Cr, Fe, Rh, and V) as SACs show good catalytic activity toward HER as their Gibbs free energies are varied between the range of –0.20 to 0.30 eV but among which Co‐SAC exhibits the highest electrochemical activity at 0.13 eV. Electronic structure studies show that the energy states of active valence dz2 orbitals and their resulting antibonding state determine the catalytic activity for HER. The fact that the antibonding state orbital is neither completely empty nor fully filled in the case of Co‐SAC is the main reason for its ideal hydrogen adsorption energy. Moreover, the electrochemical measurement shows that Co‐SAC exhibits a superior hydrogen evolution activity over Ni‐SAC and W‐SAC, confirming the theoretical calculation. This systematic study gives a fundamental understanding about the design of highly efficient SACs for HER.
The origin of single atom catalytic activity for hydrogen evolution reaction is explored via mutual collaboration of computational prediction and experimental validation. It is found that single atom catalytic activity depends on their valence orbital states, showing excellent correlation with charge transfer and activity descriptors. This systematic study will open a new direction to design heterogeneous catalysts for hydrogen evolution reaction.
Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the ...strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well.
Inversion symmetry broken 2D 3R‐MoTe2 single crystals are synthesized by chemical vapor deposition for the first time. Such a novel noncentrosymmetric structure renders it with high frequency conversion efficiency in second harmonic generation and strong spin–orbit coupling, suggesting its promising future in the applications of nonlinear optics and valleytronics.
China has committed to reaching carbon neutrality by 2060, which will require a drastic cut in greenhouse gas (GHG) emissions from all sectors, including those from agricultural activities. A ...comprehensive, long-term, and spatially-precise profile of agricultural GHG emissions can help to accurately understand drivers of historical emissions and their implications for future mitigation. This study constructs province-level agricultural GHG emissions in China from 1978 to 2016. It considers primary and secondary emissions from a full range of agricultural activities related to crop farming, including crop residue open burning, rice cultivation, cropland change, cropland emissions, machinery use, nitrogen fertilizer production, and pesticide production. Annual or interpolated activity data from official sources and the latest emission factors available for China were adopted in this study. The data can be used in spatial and temporal analysis of emissions from cropping systems as well as the design of mitigation strategy in China.
The atomic thin, vertically-stacked 2H-MoTe2/MoS2 heterostructures are successfully synthesized using the single step chemical vapor deposition (CVD) method and a magnet-assisted secondary precursor ...delivery tool. The second material (MoTe2) was grown in a well-controlled, unique and epitaxial 2H-stacking mode atop the first material (MoS2), starting from the edges. This led to the construction of a vertical p-n junction with a broadband photoresponse from the ultraviolet (UV, 200 nm) to the near-infrared (IR, 1100 nm) regions. The high crystallinity of MoTe2/MoS2 heterostructures with a modulation of sulfur and tellurium distribution is corroborated by multiple characterization methods, including Raman spectroscopy, photoluminescence (PL) spectroscopy and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Furthermore, the photoelectrical measurements exhibit a tremendous photoresponsivity with an external quantum efficiency (EQE) as high as 4.71 A/W and 532% at 1100 nm, while as 4.67 A/W and 1935% at 300 nm, one to two orders of magnitude higher than other exfoliated MoTe2 heterostructure devices have been reported so far. This synthetic method is a controllable stacking mode confined synthesis approach for 2D heterostructures, and paves the way for the fabrication of high-performance functional telluride-based broadband photodetectors.
Highly crystallized bilayer MoTe2/MoS2 p-n heterojunctions with advanced photoresponsivity are for the first time synthesized by a single-run chemical vapor deposition method. The photodetectors exhibit a tremendous photoresponsivity as 4.71 A/W and an external quantum efficiency (EQE) as 532% at 1100 nm, while 4.67 A/W and 1935% at 300 nm, which are one to two orders of magnitude higher than other transition-metal dichalcogenides (TMDs) heterostructures reported so far. Display omitted
The privatization of collectively used rangelands results in fragmentation of land use in pastoral areas. This affects pastoralists' grazing strategies and results in new institutional arrangements ...for addressing changing social-ecological systems. Two main systems of grazing management have emerged in the pastoral regions of the Qinghai-Tibetan Plateau that offer new perspectives on addressing rangeland fragmentation. One allows the renting of parcels of allocated grazing land to or from others (RTS) and is based on having fenced contracted parcels for each household. The other is a community-based grazing quota system (GQS) in which a grazing use quota is allocated to each household, while the community maintains collective use of the rangeland. We compare two case study villages implementing these two different management systems, operating across household and community scales, and analyze vegetation composition, above-ground biomass, and soil properties as indicators of impacts. Transects reveal that aboveground biomass was higher under the RTS than under the GQS, but species composition shifted to dominance by non-palatable forbs and graminoids. The RTS grasslands had lower carbon and nitrogen density compared to GQS-managed grasslands. These differences are consistent with the herder's perceptions of ecological changes. The general improvement of rangeland conditions under the GQS may be linked to greater herd mobility and the control of livestock numbers through the establishment of community-enforced grazing quotas. Mobility under the RTS is limited to a few parcels, and local regulation of stocking rates is minimal because the system relies on external intervention. The case of GQS suggests that addressing rangeland fragmentation with improved vegetation conditions requires institutions operating at both household and community scales allowing for mobility and regulation of stocking rates.
Organic fertilizer is an effective substitute for mineral fertilizer that improves crop yield and is environmentally friendly. However, the effects of substitution often vary due to complicated ...interactions among the organic fertilizer substitution rate (Rs), total nutrient supply, and type of cropping system used. We performed a meta-analysis of 133 maize studies, conducted worldwide, to assess maize yield and environmental performance with substitution of mineral fertilizer with organic fertilizer. At an equivalent nitrogen (N) rate, substituting mineral fertilizer with organic fertilizer increased maize yield by 4.22%, reduced NH3 volatilization by 64.8%, reduced N leaching and runoff by 26.9%, and increased CO2 emissions by 26.8%; however, it had no significant effect on N2O or CH4 emissions. Moreover, substitution with organic fertilizer increased the soil organic carbon sequestration rate by 925 kg C ha−1 yr−1 and decreased the global warming potential by 116 kg CO2 eq ha−1 compared with mineral fertilizer treatment. The net global warming potential after organic fertilizer substitution was −3507 kg CO2 eq ha−1, indicating a net carbon sink. Furthermore, the effect of organic fertilizer substitution varied with the fertilization rate, Rs, and treatment duration. Maize yield and nitrogen use efficiency tended to increase with increasing N application rate following substitution of mineral fertilizer with organic fertilizer. Full substitution reduced N losses more than partial substitution. Further analysis revealed that the yield-optimal Rs for organic N in maize production was 40–60%. Moreover, maize yield and nitrogen use efficiency were further increased after long-term (≥ 3 years) combined use of organic and mineral fertilizers. These findings suggest that rational use of organic and mineral fertilizers improves maize productivity, increases soil organic carbon sequestration, and reduces N and C losses.
The increase in tropospheric ozone (O3) affects plant physiology and ecosystem processes, and consequently the cycle of nutrients. While mineral nutrients are critical for plant growth, the effect of ...elevated tropospheric O3 concentration on the uptake and allocation of mineral nutrients by plants is not well understood. Using open top chambers (OTCs), we investigated the effect of elevated O3 on calcium (Ca), magnesium (Mg) and iron (Fe) in mature bamboo species Phyllostachys edulis and Oligostachyum lubricum. Our results showed that elevated O3 decreased the leaf biomass of P. edulis and O. lubricum by 35.1% and 26.7%, respectively, but had no significant effect on the biomass of branches, stem or root. For P. edulis, elevated O3 increased the nutrient (Ca, Mg and Fe) concentration and allocation in leaf but reduced the concentration in other organs. In contrast, elevated O3 increased the nutrient concentration and allocation in the branch of O. lubricum but decreased that of other organs. We also found that that P. edulis and O. lubricum responded differently to elevated O3 in terms of nutrient (Ca, Mg and Fe) uptake and allocation. This information is critical for nutrient management and adaptation strategies for sustainable growth of P. edulis and O. lubricum under global climate change.
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•Elevated O3 altered the mineral nutrients content of different bamboos organs.•The response of nutrient uptake to elevated O3 varied with bamboo species.•Proper nutrient management of bamboo forests under climate change is critical.
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