Excessive climate warming exacerbates nitrogen limitation on microbial metabolism in an alpine meadow of the Tibetan Plateau: Evidence from soil ecoenzymatic stoichiometry.

Soil ecoenzymatic stoichiometry reflects the dynamic equilibrium between microorganism's nutrient requirements and resource availability. However, uncertainties persist regarding the key determinants of nutrient restriction in relation to microbial metabolism under varying degrees of warming. Our long-term and multi-level warming field experiment (control treatment, +0.42 °C, +1.50 °C, +2.55 °C) in a typical alpine meadow unveiled a decline in carbon (C)- and nitrogen (N)-acquired enzymes with escalating warming magnitudes, while phosphorus (P)-acquired enzymes displayed an opposite trend. Employing enzymatic stoichiometry modeling, we assessed the nutrient limitations of microbial metabolic activity and found that C and N co-limited microbial metabolic activities in the alpine meadow. Remarkably, high-level warming (+2.55 °C) exacerbated microbe N limitation, but alleviate C limitations. The structural equation modeling further indicated that alterations in soil extracellular enzyme characteristics (SES) were more effectively elucidated by microbial characteristics (microbial biomass C, N, P, and their ratios) rather than by soil nutrients (total nutrient contents and their ratios). However, the microbial control over SES diminished with higher levels of warming magnitude. Overall, our results provided novel evidence that the factors driving microbe metabolic limitation may vary with the degree of warming in Tibet alpine grasslands. Changes in nutrient demand for microorganism's metabolism in response to warming should be considered to improve nutrient management in adapting to different future warming scenarios.

Climate warming alters the relative importance of plant root and microbial community in regulating the accumulation of soil microbial necromass carbon in a Tibetan alpine meadow.

Climate warming is predicted to considerably affect variations in soil organic carbon (SOC), especially in alpine ecosystems. Microbial necromass carbon (MNC) is an important contributor to stable soil organic carbon pools. However, accumulation and persistence of soil MNC across a gradient of warming are still poorly understood. An 8-year field experiment with four levels of warming was conducted in a Tibetan meadow. We found that low-level (+0-1.5°C) warming mostly enhanced bacterial necromass carbon (BNC), fungal necromass carbon (FNC), and total MNC compared with control treatment across soil layers, while no significant effect was caused between high-level (+1.5-2.5°C) treatments and control treatments. The contributions of both MNC and BNC to soil organic carbon were not significantly affected by warming treatments across depths. Structural equation modeling analysis demonstrated that the effect of plant root traits on MNC persistence strengthened with warming intensity, while the influence of microbial community characteristics waned along strengthened warming. Overall, our study provides novel evidence that the major determinants of MNC production and stabilization may vary with warming magnitude in alpine meadows. This finding is critical for updating our knowledge on soil carbon storage in response to climate warming.

Ligand-Engineered Quantum Dots Decorated Heterojunction Photoelectrodes for Self-Biased Solar Water Splitting.

A cost-effective and high-efficiency photoelectrochemical (PEC) water splitting system based on colloidal quantum dots (QDs) represents a potential solar-to-hydrogen (STH) conversion technology to achieve future carbon neutrality. Herein, a self-biased PEC cell consisting of BiVO4 photoanode and Cu2 O photocathode both decorated with Zn-doped CuInS2 (ZCIS) QDs is successfully fabricated. The intrinsic charge dynamics of the photoelectrodes are efficiently optimized via rational engineering of the surface ligands capped on QDs with controllable chain lengths and binding affinities to the metal oxide electrodes. It is demonstrated that the short-chain monodentate 1-dodecanethiol ligands are beneficial to ZCIS QDs for suppressing charge recombination, which enables the construction of tight heterojunction with coupled metal oxide electrodes, leading to effective photo-induced charge transfer/injection for enhanced PEC performance. The QD decorated BiVO4 and Cu2 O photoelectrodes in pairs demonstrate a self-biased PEC water splitting process, delivering an STH efficiency of 0.65% with excellent stability under AM 1.5 G one-sun illumination. The results highlight the significance of synergistic ligand and heterojunction engineering to build highly efficient and robust QDs-based PEC devices for self-biased solar water splitting.

Engineered Environment-Friendly Colloidal Core/Shell Quantum Dots for High-Efficiency Solar-Driven Photoelectrochemical Hydrogen Evolution.

"Green" colloidal quantum dots (QDs)-based photoelectrochemical (PEC) cells are promising solar energy conversion systems possessing environmental friendliness, cost-effectiveness, and highly efficient solar-to-hydrogen conversion. In this work, eco-friendly AgInSe (AISe)/ZnSe core/shell QDs with wurtzite (WZ) phase were synthesized for solar hydrogen production. It was demonstrated that appropriately engineering the ZnSe shell thickness resulted in effective surface defects passivation of the AISe core for suppressed charge recombination in the consequent core/shell AISe/ZnSe QDs. The fabricated environmentally friendly core/shell QDs-based PEC device exhibited improved photo-excited electrons extraction efficiency under optimized conditions and delivered a maximum photocurrent density as high as 7.5 mA cm-2 and long-term durability under standard AM 1.5G illumination (100 mW cm-2 ). These findings suggest that AISe/ZnSe core/shell QDs with tailored optoelectronic properties are potential light sensitizers for eco-friendly, cost-effective, and highly efficient solar energy conversion applications.

Decoration of BiVO4 Photoanodes with Near-Infrared Quantum Dots for Boosted Photoelectrochemical Water Oxidation.

Broadening light absorption and improving charge carrier separation are very critical to boost the water splitting efficiency in photoelectrochemical (PEC) systems. We herein reported a heterostructured photoanode consisting of BiVO4 and eco-friendly, near-infrared (NIR) CuInSeS@ZnS core-shell quantum dots (QDs) for PEC water oxidation. The decoration of core-shell QDs concurrently extends the absorption range of BiVO4 from the ultraviolet-visible to NIR region and promotes the effective separation and transfer of photo-excited electrons and holes. Without any sacrificial agents and co-catalysts, the as-fabricated NIR core-shell QDs/BiVO4 heterostructured photoanodes exhibit an approximately fourfold higher photocurrent density than that of the bare BiVO4, up to 3.17 mA cm-2 at 1.23 V versus the reversible hydrogen electrode. It is revealed that both a suitable band alignment and an intimate interfacial junction between QDs and BiVO4 are the main factors that result in enhanced charge separation and transfer efficiencies. We also highlight that the NIR CISeS QDs passivated with a ZnS shell can suppress the non-radiative recombination and enhance the stability of the QD photoanodes for optimized PEC performance. This work provides a facile and effective approach to boost the water oxidation efficiency of semiconductor photoanodes via utilizing NIR core-shell QDs as a light sensitizer and charge carrier separator.

Erratum: One-Step Construction of Hydrophobic MOFs@COFs Core-Shell Composites for Heterogeneous Selective Catalysis.

[This corrects the article DOI: 10.1002/advs.201802365.].

Accelerating charge transfer at an ultrafine NiFe-LDHs/CB interface during the electrocatalyst activation process for water oxidation.

Owing to the combination of intriguing activity and conductivity, hybrid compositions of layered double hydroxides (LDHs) and carbon-based materials have been extensively and widely applied to evolve oxygen gas during water splitting. Here, a facile in situ nucleation strategy was used to construct ultrafine NiFe-LDH nanosheets monodispersed on a carbon black (CB) substrate. Notably, this work displayed the interfacial impact of combining CB with NiFe-LDHs on electrocatalyst activation. Interestingly, the optimized NiFe-LDHs/CB composite displays a fast activation rate and excellent water oxidation performance on a glassy-carbon electrode (an overpotential of 226 mV at 10 mA cm-2; a Tafel slope of 57 mV dec-1). This is due to the high active area, low impedance and ultra-high active metal atom utilization rate, accelerating charge transfer at the interface during the activation process. More importantly, this work highlights the interfacial charge transfer effect during the activation process and supplies clues for designing electrocatalysts.

Amino-Induced 2D Cu-Based Metal-Organic Framework as an Efficient Heterogeneous Catalyst for Aerobic Oxidation of Olefins.

With the assistance of hydrogen bonds of the o-amino group, we have successfully tuned a coordination structure from a metal-organic polyhedron (MOP) to a two-dimensional (2D) metal-organic framework (MOF). The amino group forms hydrogen bonds with the two vicinal carboxylic groups, and induces the ligand to coordinate with copper ions to form the 2D structure. The obtained 2D Cu-based MOF (Cu-AIA) has been applied as an efficient heterogeneous catalyst in the aerobic epoxidation of olefins by using air as oxygen source. Without the aggregation problem of active sites in MOPs, Cu-AIA possesses much higher reactivity than MOP-1. Furthermore, the amino group of the framework has been used as a modifiable site through post-synthetic metalation (PSMet) to prepare a 2D MOF-supported Pd single-site heterogeneous catalyst, which shows excellent catalytic performance for the Suzuki reaction. It indicates that Cu-AIA can also work as a good 2D MOF carrier for the derivation of other heterogeneous catalysts.

Hollow Cobalt Phosphide with N-Doped Carbon Skeleton as Bifunctional Electrocatalyst for Overall Water Splitting.

The development of cost-effective, high-performance, and robust bifunctional electrocatalysts for overall water splitting remains highly desirable yet quite challenging. Here, by selecting appreciate precursors of dopamine and a Co-containing metal-organic framework of ZIF-67, we subtly couple their reaction processes to develop a facile approach for the synthesis of a hollow CoP nanostructure with N-doped carbon skeleton (H-CoP@NC). Benefiting from the highly porous nanostructure and conductive carbon skeleton, H-CoP@NC is capable of working as highly active and durable bifunctional electrocatalyst for both hydrogen and oxygen evolution reaction. When further used as the electrocatalyst for overall water splitting, H-CoP@NC delivers excellent activity (cell voltage of 1.72 V at a current density of 10 mA cm-2), close to that of the noble-metal-based benchmark catalyst couple of Pt/C||RuO2. Our work thus provides new insights into the development of transitional metal phosphides based hollow hybrid nanostructures, particularly those with multiple functionalities in sustainable energy conversion technologies and systems.

One-Step Construction of Hydrophobic MOFs@COFs Core-Shell Composites for Heterogeneous Selective Catalysis.

The exploration of novel porous core-shell materials is of great significance because of their prospectively improved performance and extensive applications in separation, energy conversion, and catalysis. Here, mesoporous metal-organic frameworks (MOFs) NH2-MIL-101(Fe) as a core generate a shell with mesoporous covalent organic frameworks (COFs) NUT-COF-1(NTU) by a covalent linking process, the composite NH2-MIL-101(Fe)@NTU keeping retentive crystallinity with hierarchical porosity well. Importantly, the NH2-MIL-101(Fe)@NTU composite shows significantly enhanced catalytic conversion and selectivity during styrene oxidation. It is mainly due to the hydrophilic MOF nanocrystals readily gathering the hydrophobic reactants styrene and boosting the radical mechanism path after combining the hydrophobic COFs shell. The synthetic strategy in this systematic study develops a new rational design for the synthesis of other core-shell MOF/COF-based hybrid materials, which can expand the promising applications.

Interfacial Electronic Structure Modulation of NiTe Nanoarrays with NiS Nanodots Facilitates Electrocatalytic Oxygen Evolution.

Interface engineering has been recognized as one of the most promising strategies for regulating the physical and chemical properties of materials. However, constructing well-defined nanointerfaces with efficient oxygen evolution reaction (OER) still remains a challenge. Herein, cross columnar NiTe nanoarrays supported on nickel foam are prepared. Subsequently, NiTe/NiS nanointerfaces are constructed by an ion-exchange process. Importantly, the electrocatalytic performance for the OER can be facilitated by coupling NiTe and NiS. As a result, NiTe/NiS shows excellent OER activity with an ultralow overpotential of only 257 mV at a current density of 100 mA cm-2 , and a Tafel slope of 49 mV dec-1 in 1.0 m KOH. The calculated and experimental results reveal that the strong electron interaction on nanointerfaces induces electronic structure modulation, which optimizes the binding energy of *OOH intermediates, thus improving the OER performance.

MOF-derived Mn doped porous CoP nanosheets as efficient and stable bifunctional electrocatalysts for water splitting.

Searching for highly active and stable bifunctional electrocatalysts for overall water splitting, e.g., for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is dominating in terms of bringing future renewable energy storage and conversion processes to reality. In this work, a kind of two-dimensional ultrathin manganese (Mn) doped polyhedral cobalt phosphide (Mn-CoP) has been synthesized via the etching-carbonization-phosphidation of Co-centered metal-organic frameworks. The as-prepared porous Mn-CoP nanosheets had a larger specific surface area and higher porosity, furnishing them with more plentiful catalytically active sites than their counterpart hollow CoP and Mn-CoP nanoparticles, and thus showed much better electrocatalytic activity for both HER and OER in acidic and alkaline media. In addition, the Mn-CoP nanosheets also demonstrated excellent durability after long-term operation. These high performances are attributed to the synergistic effects of the CoP nanosheets with intrinsic activity, the graphitic carbon and the controllable electronic structure doped by Mn and N elements. This synthetic methodology of using a classical MOF as a precursor to build a new 2D sheet-like composite may create opportunities to search for highly efficient and robust non-precious metal catalysts for energy-related reactions.