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Electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e--ORR) provides an alternative method to the energy-intensive anthraquinone method. Metal macrocycles with precise coordination are widely used for 2e--ORR electrocatalysis, but they have to be commonly loaded on conductive substrates, thus exposing a large number of 2e--ORR-inactive sites that result in poor H2O2 production rate and efficiency. Herein, guided by first-principle predictions, a substrate-free and two-dimensional conductive metal-organic framework (Ni-TCPP(Co)), composed of Co-N4 sites in porphine(Co) centers and Ni2O8 nodes, is designed as a multi-site catalyst for H2O2 electrosynthesis. The approperiate distance between the CoN4 and Ni2O8 sites in Ni-TCPP(Co) weakens the electron transfer between them, thus ensuring their inherent activities and creating high-density active sites. Meanwhile, the intrinsic electronic conductivity and porosity of Ni-TCPP(Co) further facilitate rapid reaction kinetics. Therefore, outstanding 2e--ORR electrocatalytic performance has been achieved in both alkaline and neutral electrolytes (>90%/85% H2O2 selectivity within 0-0.8 V vs. RHE and >18.2/18.0 mol g-1 h-1 H2O2 yield under alkaline/neutral conditions), with confirmed feasibility for water purification and disinfection applications. This strategy thus provides a new avenue for designing catalysts with precise coordination and high-density active sites, promoting high-efficiency electrosynthesis of H2O2 and beyond.
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Designing non-noble metal single-atom catalysts (M-SACs) for two-electron oxygen reduction reaction (2e-ORR) is attractive for the hydrogen peroxide (H2O2) electrosynthesis, in which the coordination configuration of the M-SACs essentially affects the reaction activity and product selectivity. Though extensively investigated, a generalized coordination engineering strategy has not yet been proposed, which fundamentally hinders the rational design of M-SACs with optimized catalytic capabilities. Herein, a generalized coordination engineering strategy is proposed for M-SACs toward H2O2 electrosynthesis via introducing heteroatoms (e.g., oxygen or sulfur atoms) with higher or lower electronegativity than nitrogen atoms into the first sphere of metal-N4 system to tailor their electronic structure and adjust the adsorption strength for *OOH intermediates, respectively, thus optimizing their electrocatalytic capability for 2e-ORR. Specifically, the (O, N)-coordinated Co SAC (Co-N3O) and (S, N)-coordinated Ni SAC (Ni-N3S) are precisely synthesized, and both present superior 2e-ORR activity (Eonset: ≈0.80 V versus RHE) and selectivity (≈90%) in alkaline conditions compared with conventional Co-N4 and Ni-N4 sites. The high H2O2 yield rates of 14.2 and 17.5 moL g-1 h-1 and long-term stability over 12 h are respectively achieved for Co-N3O and Ni-N3S. Such favorable 2e-ORR pathway of the catalysts is also theoretically confirmed by the kinetics simulations.
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Electrocatalytic hydrogen peroxide (H2O2) production via two-electron oxygen reduction reaction (2e--ORR) features energy-saving and eco-friendly characteristics, making it a promising alternative to the anthraquinone oxidation process. However, the common existence of numerous 2e--ORR-inactive sites/species on electrocatalysts tends to catalyze side reactions, especially under low potentials, which compromises energy efficiency and limits H2O2 yield. Addressing this, a high surface density of mono-species pyrrolic nitrogen configurations is formed over a polypyrrole@carbon nanotube composite. Thermodynamic and kinetic calculation and experimental investigation collaboratively confirm that these densely distributed and highly selective active sites effectively promote high-rate 2e--ORR electrocatalysis and inhibit side reactions over a wide potential range. Consequently, an ultra-high and stable H2O2 yield of up to 67.9/51.2 mol g-1 h-1 has been achieved on this material at a current density of 200/120 mA cm-1, corresponding Faradaic efficiency of 72.8/91.5%. A maximum H2O2 concentration of 13.47 g L-1 can be accumulated at a current density of 80 mA cm-1 with satisfactory stability. The strategy of surface active site densification thus provides a promising and universal avenue toward designing highly active and efficient electrocatalysts for 2e--ORR as well as a series of other similar electrochemical processes.
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Rice is a staple food for more than half of humanity, and 90 % of rice is grown and consumed in Asia. However, paddy rice cultivation creates an ideal environment for the production and release of methane (CH4). How to estimate regional CH4 emissions accurately and how to mitigate them efficiently have been of key concern. Here, with a machine learning method, we investigate the spatiotemporal changes, the major controlling factors and mitigation potentials of paddy rice CH4 emissions across Monsoon Asia at a resolution of 0.1° (â¼10 km). Spatially CH4 emissions are highly heterogeneous, with the Indo-Gangetic Plain, Deltas of the Mekong, and Yangtze River Basin as the hotspots. Nationwide, China, India, Bangladesh and Vietnam are the major emitters. Straw applied on season is a critical controlling factor for CH4 emission in rice fields. The single-season rice contributes to over 80 % of the total emissions. CH4 emissions from Monsoon Asia have notably declined since 2007. Three mitigation strategies, including water management techniques, off-season straw return, and straw to biochar, may reduce CH4 emissions by 27.66 %, 23.78 %, and 21.79 %, respectively, with the most effective strategy being rice cultivation type-specific and environment-specific. Our findings gain new insights into CH4 emissions and mitigations across Monsoon Asia, providing evidence to adopt precise mitigation strategies based on rice cultivation types and local environment.
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Developing narrow-band-gap ferroelectric semiconducting photocatalysts is a promising strategy for efficient photocatalytic water splitting with high energy conversion efficiency. Within this context, six ferro/nonferroelectric vertical heterostructure superlattices (VHSs) are constructed in this work by stacking ferroelectric SiS or GeS with nonferroelectric layered organic photocatalysts (C2N, g-C3N4, and melon), layer by layer. The geometry and electronic structures of these six VHSs are systematically investigated by density functional theory calculations. Consequently, four VHSs (SiS/g-C3N4, GeS/C2N, GeS/g-C3N4, and GeS/melon) are predicted to simultaneously possess several important and highly desirable features for photocatalytic water splitting, namely excellent visible-light adsorption, remarkable spontaneous polarization (0.49-0.70 C/m2), spatial charge separation, as well as suitable band-edge positions, thus serving as potential candidates for photocatalytic water splitting to produce hydrogen. This work not only provides a new strategy to use narrow-band-gap ferroelectric semiconductors for photocatalytic water splitting but also offers inspiration for developing photocatalysts with high energy conversion efficiency.
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Bi3TiNbO9, a layered ferroelectric photocatalyst, exhibits great potential for overall water splitting through efficient intralayer separation of photogenerated carriers motivated by a depolarization field along the in-plane a-axis. However, the poor interlayer transport of carriers along the out-of-plane c-axis, caused by the significant potential barrier between layers, leads to a high probability of carrier recombination and consequently results in low photocatalytic activity. Here, we have developed an efficient photocatalyst consisting of Bi3TiNbO9 nanosheets with a gradient tungsten (W) doping along the c-axis. This results in the generation of an additional electric field along the c-axis and simultaneously enhances the magnitude of depolarization field within the layers along the a-axis due to strengthened structural distortion. The combination of the built-in field along the c-axis and polarization along the a-axis can effectively facilitate the anisotropic migration of photogenerated electrons and holes to the basal {001} surface and lateral {110} surface of the nanosheets, respectively, enabling desirable spatial separation of carriers. Hence, the W-doped Bi3TiNbO9 ferroelectric photocatalyst with Rh/Cr2O3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.
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Hybrid cocatalysts have great application potential for improving the photocatalytic hydrogen evolution performance of semiconductors. The interfaces between components of hybrid cocatalysts make a great contribution to the improvement, but the associated mechanisms remain unclear. Herein, we prepared and tested three comparative CdS-based photocatalysts with NiS, NiS/Ni9S8, and Ni9S8 as the cocatalysts separately. The emphasis is placed on investigating the effect of the NiS/Ni9S8 interfaces on the photocatalytic hydrogen evolution performance of CdS. NiS/Ni9S8 exhibits a higher ability than NiS and Ni9S8 in making CdS a more active photocatalyst for water splitting. It shows that NiS, NiS/Ni9S8, and Ni9S8 perform similarly in terms of promoting the charge transfer and separation of CdS based on steady-state and time-resolved photoluminescence studies. At the same time, the linear sweep voltammetry and electrochemical impedance spectroscopy tests combined with the density functional theory calculations reveal that the component interfaces of NiS/Ni9S8 enable us to lower the water splitting activation energy, the charge-transfer resistance from the cocatalyst to sacrificial agent, and hydrogen adsorption Gibbs free energy. It is evidenced from this work that component interfaces of hybrid cocatalysts play a vital role in accelerating the dynamics of hydrogen evolution reactions.
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Single-atom nanozymes (SANs) are the latest trend in biomaterials research and promote the application of single atoms in biological fields and the realization of protein catalysis in vivo with inorganic nanoparticles. Carbon quantum dots (CDs) have excellent biocompatibility and fluorescence properties as a substrate carrying a single atom. It is difficult to break through pure-phase single-atom materials with quantum dots as carriers. In addition, there is currently no related research in the single-atom field in the context of oral cancer, especially head and neck squamous cell carcinoma. This research developed a lipid surface-coated nanozyme combined with CDs, single-atomic gold, and modified lipid ligands (DSPE-PEG) with transferrin (Tf) to treat oral squamous cell carcinoma. The study results have demonstrated that surface-modified single-atom carbon quantum dots (m-SACDs) exhibit excellent therapeutic effects and enable in situ image tracking for diagnosing and treating head and neck squamous carcinoma (HNSCC).
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Carcinoma de Células Escamosas , Neoplasias Bucais , Fotoquimioterapia , Humanos , Carcinoma de Células Escamosas/patologia , Neoplasias Bucais/tratamento farmacológico , Carbono/química , Estresse Oxidativo , Lipídeos/químicaRESUMO
Evapotranspiration (ET) is a key variable in the water cycle and reflects the ecosystem's feedback into the climate system. However, quantitative studies on the response of ET to large-scale vegetation restoration projects and climate change are still lacking, especially in drylands. To address this deficiency, this research examined the variation in ET since the implementation of restoration projects in the drylands of China in 2000-2018, and utilized quantitative analysis methods to investigate the effects of six environmental factors, including temperature (TEM), precipitation (PRE), solar radiation (RAD), vapour pressure deficit (VPD), soil moisture (SM), and leaf area index (LAI) on ET. Furthermore, a new method was proposed to detect the ET change caused by land use and land cover change (LUCC). The results indicated that ET showed a significant increasing trend (3.54 mm yr-1) during 2000-2018, and PRE was identified as a main influential factor with an ET contribution rate of more than 50%, especially in areas with insignificant vegetation greening. Additionally, the LAI had a major positive impact on ET in the areas of significant vegetation greening, and the contribution rate was nearly 40%. Furthermore, large-scale vegetation restoration expanded the area of high-transpiration vegetation types, and the ΔET (net variable quantity of ET caused by LUCC) increased obviously especially for the changes from cropland and grassland to forest, and barren land to grassland. These findings provide a new perspective for future assessments and further decision making regarding vegetation restoration projects in drylands.
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Ecossistema , Solo , Florestas , China , Mudança Climática , PolíticasRESUMO
Electrocatalytic hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H2O2 yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e- oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H2O2 production. Consequently, the H2O2 yield approaches 30 mol g-1 h-1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H2O2 concentration of 7.2 g L-1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e- oxygen reduction.
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Aurivillius-type compounds ((Bi2 O2 )2+ (An -1 Bn O3 n +1 )2- ) with alternately stacked layers of bismuth oxide (Bi2 O2 )2+ and perovskite (An -1 Bn O3 n +1 )2- are promising photocatalysts for overall water splitting due to their suitable band structures and adjustable layered characteristics. However, the self-reduction of Bi3+ at the top (Bi2 O2 )2+ layers induced by photogenerated electrons during photocatalytic processes causes inactivation of the compounds as photocatalysts. Here, using Bi3 TiNbO9 as a model photocatalyst, its surface termination is modulated by acid etching, which well suppresses the self-corrosion phenomenon. A combination of comprehensive experimental investigations together with theoretical calculations reveals the transition of the material surface from the self-reduction-sensitive (Bi2 O2 )2+ layer to the robust (BiTiNbO7 )2- perovskite layer, enabling effective electron transfer through surface trapping and effective hole transfer through surface electric field, and also efficient transfer of the electrons to the cocatalyst for greatly enhanced photocatalytic overall water splitting. Moreover, this facile modification strategy can be readily extended to other Aurivillius compounds (e.g., SrBi2 Nb2 O9 , Bi4 Ti3 O12 , and SrBi4 Ti4 O15 ) and therefore justify its usefulness in rationally tailoring surface structures of layered photocatalysts for high photocatalytic overall water-splitting activity and stability.
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Aqueous Zn-based batteries (ZIBs) possess huge advantages in terms of high safety, low cost, and environmental friendliness. However, the lack of suitable cathodes with high-capacity, long-cycling, and high-rate capability limits their practical application. Herein, we present a highly crystalline one-dimensional π-d conjugated conductive metal-organic framework by coordinating ultrasmall 1,2,4,5-benzenetetramine (BTA) linkers with copper ions (Cu-BTA-H), as a cathode for ZIBs. The large ratio of active sites and dual redox mechanism of Cu-BTA-H, including the one-electron-redox reaction over copper ions (via Cu2+/Cu+) and the two-electron-redox reaction over organic ligands (via CâN/C-N), effectively enhance its reversible capacity. Meanwhile, the abundant porosity, small band gap, high crystallinity, and stable coordination structure of Cu-BTA-H endow it with fast ion/electron transport and effectively hinder the dissolution of organic ligands during cycling, respectively. Consequently, Cu-BTA-H possesses a high reversible capacity of 330 mAh g-1 at 200 mA g-1 and excellent rate performance and long-cycle stability, with a high capacity of 106.1 mAh g-1 at 2.0 A g-1 after 500 cycles and a high Coulombic efficiency of â¼100%. The proposed conductive MOFs with dual redox-active sites provide an efficient approach for constructing fast, stable, and high-capacity energy storage devices.
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Using hydrogen as a fuel is an effective way to combat energy crisis and at the same time reduce greenhouse gas emission. Alkaline hydrogen evolution reaction (HER) is one important way to obtain green hydrogen, which however is energy intensive and is difficult to obtain high efficiencies even when using state-of-the-art noble metal catalysts. Here, we report a three-component catalytic system using only non-noble elements, consisting of cobalt oxide clusters and single molybdenum atoms supported on oxyanion-terminated two-dimensional MXene, which enabled the unusual generation of hydrogen by a kinetically fast Volmer-Tafel process in an alkaline electrolyte. The key feature of this catalyst is that the three components are connected by bridging oxygen, which serves to immediately adsorb H* produced during water dissociation on cobalt oxide and relay it to the molybdenum single-atom catalyst. On the Mo atom, due to this unique coordination environment, the relayed H* intermediates directly combine and desorb, realizing H2 generation through an unusual Tafel pathway. The presence of bridging oxygen increases the acidity of the catalyst as Brønsted acid with the reversible adsorption and donation of a proton, thus eliminating the need for acid addition and ensuring excellent and sustainable alkaline HER performance. The performance of our catalyst is comparable to that of the commercial noble metal catalyst PtRu/C. Our work makes a significant contribution to designing efficient non-noble catalysts for alkaline HER electrocatalysis.
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Hydroxyl radical-dominated oxidation in catalytic ozonation is, in particular, important in water treatment scenarios for removing organic contaminants, but the mechanism about ozone-based radical oxidation processes is still unclear. Here, we prepared a series of transitional metal (Co, Mn, Ni) single-atom catalysts (SACs) anchored on graphitic carbon nitride to accelerate ozone decomposition and produce highly reactive ·OH for oxidative destruction of a water pollutant, oxalic acid (OA). We experimentally observed that, depending on the metal type, OA oxidation occurred dominantly either in the bulk phase, which was the case for the Mn catalyst, or via a combination of the bulk phase and surface reaction, which was the case for the Co catalyst. We further performed density functional theory simulations and in situ X-ray absorption spectroscopy to propose that the ozone activation pathway differs depending on the oxygen binding energy of metal, primarily due to differential adsorption of O3 onto metal sites and differential coordination configuration of a key intermediate species, *OO, which is collectively responsible for the observed differences in oxidation mechanisms and kinetics.
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Ozônio , Poluentes Químicos da Água , Purificação da Água , Radical Hidroxila/química , Oxirredução , Metais , Catálise , Ácido Oxálico/química , Poluentes Químicos da Água/química , Purificação da Água/métodosRESUMO
Ferroelectric materials hold great promise in the field of photocatalytic water splitting due to their spontaneous polarization that sets up an inherent internal field for the spatial separation of photogenerated charges. The ferroelectric polarization, however, is generally accompanied by some intrinsic defects, particularly oxygen vacancies, whose impact upon photocatalysis is far from being fully understood and modulated. Here, we have studied the role of oxygen vacancies over the photocatalytic behavior of single-domain PbTiO3 through a combination of theoretical and experimental viewpoints. Our results indicate that the oxygen vacancies in the negatively polarized facet (001) are active sites for water oxidation into O2, while the defect-free sites prefer H2O2 as the oxidation product. The apparent quantum yield at 435 nm for photocatalytic overall water splitting with PbTiO3/Rh/Cr2O3 is determined to be 0.025%, which is remarkable for single undoped metal oxide-based photocatalysts. Furthermore, the strong correlation among oxygen vacancies, polarization strength, and photocatalytic activity is properly reflected by charge separation conditions in the single-domain PbTiO3. This work clarifies the crucial role of oxygen vacancies during photocatalytic reactions of PbTiO3, which provides a useful guide to the design of efficient ferroelectric photocatalysts and their water redox reaction pathways.
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Ambient solution-processed conductive materials with a sufficient low work function are essential to facilitate electron injection in electronic and optoelectronic devices but are challenging. Here, we design an electrically conducting and ambient-stable polymer electrolyte with an ultralow work function down to 2.2 eV, which arises from heavy n-doping of dissolved salts to polymer matrix. Such materials can be solution processed into uniform and smooth films on various conductors including graphene, conductive metal oxides, conducting polymers and metals to substantially improve their electron injection, enabling high-performance blue light-emitting diodes and transparent light-emitting diodes. This work provides a universal strategy to design a wide range of stable charge injection materials with tunable work function. As an example, we also synthesize a high-work-function polymer electrolyte material for high-performance solar cells.
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Resource-abundant metal (e.g., zinc) batteries feature intrinsic advantages of safety and sustainability. Their practical feasibility, however, is impeded by the poor reversibility of metal anodes, typically caused by the uncontrollable dendrite enlargement. Significant effort is exerted to completely prevent dendrites from forming, but this seems less effective at high current densities. Herein, this work presents an alternative dendrite regulation strategy of forming tiny, homogeneously distributed, and identical zinc dendrites by facet matching, which effectively avoids undesirable dendrite enlargement. Confirmed by multiscale theoretical screening and characterization, the regularly exposed Cu(111) facets at the ridges of a copper nanowire are capable of such dendrite regulation by forming a low-mismatched Zn(002)/Cu(111) interface. Consequently, reversible zinc electroplating/stripping is achieved at an unprecedentedly high rate of 100 mA cm-2 for over 30 000 cycles, corresponding to an accumulative areal capacity up to 30 Ah cm-2 . A full cell using this anode shows a high capacity of 308.3 mAh g-1 and a high capacity retention of 91.4% after 800 cycles. This strategy is also viable for magnesium and aluminum anodes, thus opening up a promising and universal avenue toward long-life and high-rate metal anodes.
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Electrocatalytic CO2 reduction to value-added hydrocarbon products using metallic copper (Cu) catalysts is a potentially sustainable approach to facilitate carbon neutrality. However, Cu metal suffers from unavoidable and uncontrollable surface reconstruction during electrocatalysis, which can have either adverse or beneficial effects on its electrocatalytic performance. In a break from the current catalyst design path, we propose a strategy guiding the reconstruction process in a favorable direction to improve the performance. Typically, the controlled surface reconstruction is facilely realized using an electrolyte additive, ethylenediamine tetramethylenephosphonic acid, to substantially promote CO2 electroreduction to CH4 for commercial polycrystalline Cu. As a result, a stable CH4 Faradaic efficiency of 64% with a partial current density of 192 mA cm-2, thus enabling an impressive CO2-to-CH4 conversion rate of 0.25 µmol cm-2 s-1, is achieved in an alkaline flow cell. We believe our study will promote the exploration of electrochemical reconstruction and provide a promising route for the discovery of high-performance electrocatalysts.
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Surface oxygen vacancies have been widely discussed to be crucial for tailoring the activity of various chemical reactions from CO, NO, to water oxidation by using oxide-supported catalysts. However, the real role and potential function of surface oxygen vacancies in the reaction remains unclear because of their very short lifetime. Here, it is reported that surface oxygen vacancies can be well confined electrostatically for a polarization screening near the perimeter interface between Pt {111} nanocrystals and the negative polar surface (001) of ferroelectric PbTiO3. Strikingly, such a catalyst demonstrates a tunable catalytic CO oxidation kinetics from 200 °C to near room temperature by increasing the O2 gas pressure, accompanied by the conversion curve from a hysteresis-free loop to one with hysteresis. The combination of reaction kinetics, electronic energy loss spectroscopy (EELS) analysis, and density functional theory (DFT) calculations, indicates that the oxygen vacancies stabilized by the negative polar surface are the active sites for O2 adsorption as a rate-determining step, and then dissociated O moves to the surface of the Pt nanocrystals for oxidizing adsorbed CO. The results open a new pathway for tunable catalytic activity of CO oxidation.