Designed Construction of SrTiO3 /SrSO4 /Pt Heterojunctions with Boosted Photocatalytic H2 Evolution Activity.

Efficient separation of photogenerated electron-hole pairs is a crucial factor for high-performance photocatalysts. Effective electron-hole separation and migration could be achieved by heterojunctions with suitable band structures. Herein, a porous SrTiO3 /SrSO4 heterojunction is prepared by a sol-gel method at room temperature followed by an annealing process. XRD characterization suggests high crystallinity of the heterostructure. A well-defined interface between the two phases is confirmed by high-resolution (HR)TEM. The photocatalytic H2 evolution productivity of the SrTiO3 /SrSO4 heterojunction with Pt as co-catalyst reaches 396.82 µmol g-1 h-1 , which is 16 times higher than that of SrTiO3 /Pt. The boosted photocatalytic activity of SrTiO3 /SrSO4 /Pt can be ascribed to the presence of SrSO4 , which promotes the transfer and migration of photogenerated carriers by forming the heterojunction and porous structure, which provides a large amount of active sites. This novel porous heterostructure brings new ideas for the development of high-efficiency photocatalysts for H2 release.

Response of alpine vegetation function to climate change in the Tibetan Plateau: A perspective from solar-induced chlorophyll fluorescence.

Vegetation change in the Tibetan Plateau (TP) is a crucial indicator of climate change in alpine regions. Previous studies have reported an overall greening trend in the vegetation structure across the TP, especially in its northeastern part, in response to a warming climate. However, variations in the vegetation function and the possible drivers remain poorly understood. Considering the optimal temperature for plants in TP is usually higher than the current temperature, our hypothesis is the function and structure of alpine vegetation have changed synchronously over past few decades. To test this hypothesis, we analyzed satellite-observed solar-induced chlorophyll fluorescence (SIF) and leaf area index (LAI) in the Yellow River source (YRS) region in the northeastern TP to quantify the long-term trends in vegetation functional and structural states, respectively. The results suggest that from 1982 to 2018, SIF increased significantly in 77.71 % of the YRS area, resulting in a significant upward trend of 0.52 × 10-3 mW m-2 nm-1 sr-1 yr-1 (p < 0.001) for the regional-mean SIF. This represents a 16.1 % increase in SIF, which is close in magnitude to the increase in LAI over the same period. The synchronous changes between vegetation function and structure suggest that improved greenness corresponds to a similar level of change in carbon uptake across YRS. Additionally, we used a multiple regression approach to quantify the contribution of climatic factors to SIF changes in YRS. Our analyses show that the increases in SIF were primarily driven by rising temperatures. Spatially, temperature dominated SIF changes in most parts of YRS, except for certain dry parts in the northern and western YRS, where precipitation had a greater impact. Our results are crucial for a comprehensive understanding of climate regulations on vegetation structure and function in high-elevation regions.

Predicting root zone soil moisture using observations at 2121 sites across China.

Root zone soil moisture (RZSM) is particularly useful for understanding hydrological processes, plant-land-atmosphere exchanges, and agriculture- and climate-related research. This study aims to estimate RZSM across China by using a one-parameter (T) exponential filter method (EF method) together with a random forest (RF) regionalization approach and by using a large dataset containing in situ observations collected at 2121 sites across China. First, at each site, T is optimized at each of four soil layers (10-20 cm, 20-30 cm, 30-40 cm and 40-50 cm) by using 0-10-cm soil layer observations and the corresponding calibration layers. Second, an RF classifier is built for each layer according to the calibrated T values and 14 soil, climate and vegetation parameters across 2121 sites. Third, the calibrated T at each soil layer is regionalized with an established RF classifier. Spatial T maps are given for each soil layer across China. Our results show that the EF method performs reasonably well in predicting RZSM at the 10-20-cm, 20-30-cm, 30-40-cm and 40-50-cm layers, with Nash-Sutcliffe efficiency (NSE) medians of 0.73, 0.52, 0.38 and 0.27, respectively, between the observations and estimations. The T parameter shows a spatial pattern in each soil layer and is largely controlled by climate regimes. This study offers an improved RZSM estimation method using a large dataset containing in situ observations; the proposed method also has the potential to be used in other parts of the world.

Synthesis of SrTiO3 submicron cubes with simultaneous and competitive photocatalytic activity for H2O splitting and CO2 reduction.

Single crystalline strontium titanate (SrTiO3) submicron cubes have been synthesized based on a molten salt method. The submicron cubes showed superior photocatalytic activity towards both water splitting and carbon dioxide reduction, in which methane (CH4) and hydrogen (H2) were simultaneously produced. The average production rate of methane up to 8 h is 4.39 µmol g-1 h-1 but drops to 0.46 µmol g-1 h-1. However, the average production rate of hydrogen is 14.52 before 8 h but then increases to 120.23 µmol g-1 h-1 after 8 h. The rate change of the two processes confirms the competition between the H2O splitting and CO2 reduction reactions. Band structure and surface characteristics of the SrTiO3 submicron cubes were characterized by diffuse reflective UV-Vis spectroscopy, Mott-Schottky analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results reveal that the simultaneous and competitive production of methane and hydrogen is due to a thermodynamics factor, as well as the competition between the adsorption of carbon dioxide and water molecules on the surface of the faceted SrTiO3. This work demonstrates that SrTiO3 photocatalysts are efficient in producing sustainable fuels via water splitting and carbon dioxide reduction reactions.

In situ formation of oxygen vacancy in perovskite Sr(0.95)Ti(0.8)Nb(0.1)M(0.1)O3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis.

In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to create oxygen vacancies in situ after reduction for high-temperature CO2 electrolysis. Combined analysis using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to reduced Sr(0.95)Ti(0.9)Nb(0.1)O2.90 for the bare sample. By contrast, a significant concentration of oxygen vacancy is additionally formed in situ for Mn- or Cr-doped samples by reducing the oxidized Sr(0.95)Ti(0.8)Nb(0.1)M(0.1)O3.00 (M = Mn, Cr) to Sr(0.95)Ti(0.8)Nb(0.1)M0.1O2.85. The ionic conductivities of the Mn- and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3-6 times higher in a reducing atmosphere at intermediate temperatures. A remarkable chemical accommodation of CO2 molecules is achieved on the surface of the reduced and doped titanate, and the chemical desorption temperature reaches a common carbonate decomposition temperature. The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes. Direct CO2 electrolysis at composite cathodes is investigated in solid-oxide electrolyzers. The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn- or Cr-doped titanate cathodes.

In situ growth of Ni(x)Cu(1-x) alloy nanocatalysts on redox-reversible rutile (Nb,Ti)O4 towards high-temperature carbon dioxide electrolysis.

In this paper, we report the in situ growth of Ni(x)Cu(1-x) (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the Ni(x)Cu(1-x) alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized Ni(x)Cu(1-x)/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the Ni(x)Cu(1-x)/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies.