Dynamics of ecosystem carbon stocks during vegetation restoration on the Loess Plateau of China

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0-100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0-100 cm. Moreover, there was a time lag of about 15-30 years between biomass production and soil carbon sequestration in 0-100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration

Morphology, crystal structure and electronic state one-step co-tuning strategy towards developing superior perovskite electrocatalysts for water oxidation

Here, we use an electrospinning method to control the crystal structure, electronic structure and microstructure of catalysts simultaneously. The electrospun perovskite SmBaSrCoO (SBSC) possesses not only a large specific surface area but also an optimized crystal structure and electronic state, showing an excellent OER activity and durability

Postsynthesis Growth of CoOOH Nanostructure on SrCo0.6Ti0.4O3−δ Perovskite Surface for Enhanced Degradation of Aqueous Organic Contaminants

The deployment of an efficient catalyst is critical for successful application of peroxymonosulfate-based advanced oxidation processes to the rapid degradation of retardant organics in wastewater. Considering the rich properties of perovskite oxides and their drawbacks of low specific area and easy cation leaching, we reported a facile postsynthesis hydrothermal treatment method for preparing SrCo0.6Ti0.4O3-d@CoOOH (SCT@CoOOH) nanocomposite as an efficient catalyst for PMS activation here. Surprisingly, CoOOH nanosheets were grown in situ over the surface of SCT substrate, resulting in a significantly increased surface area (22.1 m2 g-1), enhanced charge transfer capability, more generated surface oxygen defects and a strongly synergistic effect created between the bulk SCT and CoOOH surface layer. Remarkably, SCT@CoOOH exhibited higher (1.7 times) catalytic activity (0.84 mg L-1 min-1) for phenol degradation than SCT. Additionally, suppressed cobalt leaching was demonstrated in the SCT@CoOOH/PMS system. Notably, singlet oxygen as additional oxidative species were formed to accelerate phenol degradation in the radical-based SCT@CoOOH/PMS system due to the surface oxygen defects. The beneficial effect of higher pH value and different influence of foreign anions on the reation rate were also investigated. As a universal method, it may be also useful for the development of innovative functional materials for other various applications

High‐performance platinum‐perovskite composite bifunctional oxygen electrocatalyst for rechargeable Zn–air battery

Constructing highly active electrocatalysts with superior stability at low cost is a must, and vital for the large-scale application of rechargeable Zn-air batteries. Herein, a series of bifunctional composites with excellent electrochemical activity and durability based on platinum with the perovskite Sr(Co0.8Fe0.2)(0.95)P0.05O3-delta (SCFP) are synthesized via a facile but effective strategy. The optimal sample Pt-SCFP/C-12 exhibits outstanding bifunctional activity for the oxygen reduction reaction and oxygen evolution reaction with a potential difference of 0.73 V. Remarkably, the Zn-air battery based on this catalyst shows an initial discharge and charge potential of 1.25 and 2.02 V at 5 mA cm(-2), accompanied by an excellent cycling stability. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure experiments demonstrate that the superior performance is due to the strong electronic interaction between Pt and SCFP that arises as a result of the rapid electron transfer via the Pt-O-Co bonds as well as the higher concentration of surface oxygen vacancies. Meanwhile, the spillover effect between Pt and SCFP also can increase more active sites via lowering energy barrier and change the rate-determining step on the catalysts surface. Undoubtedly, this work provides an efficient approach for developing low-cost and highly active catalysts for wider application of electrochemical energy devices

Postsynthesis oxygen nonstoichiometric regulation: a new strategy for performance enhancement of perovskites in advanced oxidation

Due to their flexible physiochemical properties and defect-rich structures, perovskite oxides have drawn increasing attention as efficient heterogeneous catalysts for peroxymonosulfate (PMS) activation in wastewater remediation. Herein, we reported a new nondoping strategy of postsynthesis oxygen nonstoichiometric regulation for LaMnO (LMO) at various oxygen partial pressures and calcination temperatures, named as LMO-P-T, to control its interstitial oxygen defect content, resulting in the enhancement of its catalytic activity and stability for degradation of rhodamine B (RhB). The defect structure, charge-transfer capacity, and resistance against metal leaching of LMO were thus improved. Specifically, LMO-5 bar-600 with the highest defect content presented excellent Fenton-like activity, 1.76 times that of LMO. Favorable singlet oxygen was confirmed as the dominant reactive species in the LMO-5 bar-600/PMS system, and the obtained catalysts showed satisfactory activity in a wide initial pH range. This work might provide a universal approach in designing metal oxides catalysts for efficient advanced oxidation

Manipulating cation nonstoichiometry towards developing better electrolyte for self-humidified dual-ion solid oxide fuel cells

Dual-ion (oxygen ion and proton) conducting electrolyte BaZrCeYYbO (BZCYYb) is one of the most commonly used electrolyte materials for proton conducting fuel cells (PCFCs). Here, we improve conducting property and performance of BZCYYb electrolyte through simply introducing B-site cation deficiency. Dual-ion conductivities for Ba(ZrCeYYb)O (BZCYYb-0.95) electrolyte are improved to a large extent as 2.5 times protonic conductivity (4.6 × 10 S cm at 700 °C) and 6.3 times oxygen ionic conductivity (1.2 × 10 S cm at 900 °C) compared to BZCYYb electrolyte. Low-temperature (1350 °C) sinterability of BZCYYb-0.95 is achieved for the higher concentration of defect compared to the original material (BZCYYb, 1500 °C). Meanwhile, a cell with the BZCYYb-0.95 electrolyte illustrates prominent power density of 794 mW cm at 650 °C, superior to the cell with BZCYYb (643 mW cm) at the same condition. The collaborative diffusions of dual-ion via two different conducting mechanisms enhance the cell performance with BZCYYb-0.95 electrolyte. The cell voltage and power density actually have no observable performance degradation during the course of the 300-h test. Therefore, it indicates the dual-ion diffusions of BZCYYb-0.95 electrolyte as the promising future for practical application

Monoclinic SrIrO3: an easily synthesized conductive perovskite oxide with outstanding performance for overall water splitting in alkaline solution

Fabricating efficient bifunctional catalysts for both hydrogen/oxygen evolution reactions (HER/OER) in an easy and mass-productive way is highly attractive for alkaline water electrolyzers. Perovskite oxides show compositional flexibility and high property tunability, while poor electrical conductivity and relatively low HER activity hamper their application in overall water splitting. Here, a conductive monoclinic SrIrO3 perovskite is developed as an excellent alkaline electrocatalyst with bifunctionality which can be easily synthesized under normal conditions. Toward the HER, it experiences progressive surface self-reconstruction during the activation process because of lattice Sr2+ leaching, eventually leading to a remarkable apparent activity with an approximately 11-fold enhancement at 200 mV overpotential relative to the fresh sample. Experimental and theoretical evidence reveals that etching of lattice Sr2+ in relatively less-stable SrIrO3 compared to IrO2 is crucial for triggering this self-reconstruction. Toward the OER, no obvious surface reconstruction occurs, and an overpotential of only 300 mV is required to realize 10 mA cmgeo–2, significantly lower than that for most perovskites reported previously (340–450 mV). The activated SrIrO3 from HER operation can be used alternatively as an OER electrocatalyst with further improved performance. A SrIrO3-based two-electrode water-splitting cell shows exceptional performance, that is, 1.59 V@10 mA cmgeo–2 with negligible performance degradation over 10 h

Fast cation exchange of layered sodium transition metal oxides for boosting oxygen evolution activity and enhancing durability

Cost-effective electrocatalysts with high activity and long durability for the oxygen evolution reaction (OER) are key to water splitting and rechargeable metal-air batteries. Here, we report the development of a superior OER electrocatalyst with outstanding activity, favorable durability, and stable particulate morphology based on an ex situ ultra-fast cation exchange strategy that can result in fine tuning of the atom arrangement inside the oxide lattice, thus optimizing the electrocatalytic performance. O3-phase NaCoFeO (O-NCF) is selected as the starting material, and the sodium in the oxide lattice is rapidly exchanged (several minutes) with hydronium ions (HO) in an acidic solution. The as-derived structure fine-tuned sample displays excellent OER performances in alkaline media with an ultra-low overpotential of only 234 mV at 10 mA cm in oxide-based electrocatalysts and an ultra-small Tafel slope of 34 mV dec. The exchange of HO with Na does not affect the oxidation state of cobalt and iron cations inside the oxide lattice, while protons in the inserted HO promote the formation of the hydroxyl group to improve activity. As a general strategy, such cation exchange strategy can also be applied to many other layered sodium transition metal oxides

Super-exchange interaction induced overall optimization in ferromagnetic perovskite oxides enables ultrafast water oxidation

Oxygen evolution reaction (OER) is crucial in many renewable electrochemical technologies including regenerative fuel cells, rechargeable metal–air batteries, and water splitting. It is found that abundant active sites with favorable electronic structure and high electrical conductivity play a dominant role in achieving high electrocatalytic efficiency of perovskites, thus efficient strategies need to be designed to generate multiple beneficial factors for OER. Here, highlighted is an unusual super-exchange effect in ferromagnetic perovskite oxide to optimize active sites and enhance electrical conductivity. A systematic exploration about the composition-dependent OER activity in SrCo Ru O (denoted as SCRx) (x = 0.0–1.0) perovskite is displayed with special attention on the role of super-exchange interaction between high spin (HS) Co and Ru ions. Induced by the unique Co–O–Ru super-exchange interactions, the SCR0.1 is endowed with abundant OER active species including Co/Co, Ru, and O /O, high electrical conductivity, and metal–oxygen covalency. Benefiting from these advantageous factors for OER electrocatalysis, the optimized SCR0.1 catalyst exhibits a remarkable activity with a low overpotential of 360 mV at 10 mA cm, which exceeds the benchmark RuO and most well-known perovskite oxides reported so far, while maintaining excellent durability. This work provides a new pathway in developing perovskite catalysts for efficient catalysis