Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO 2 and nitrogen across major terrestrial vegetation types of the world. Most experiments manipulated single rather than multiple global change drivers in temperate ecosystems of the USA, Europe and China. The magnitudes of warming and elevated CO 2 treatments were consistent with the ranges of future projections, whereas those of precipitation changes and nitrogen inputs often exceeded the projected ranges. Increases in global change drivers consistently accelerated, but decreased precipitation slowed down carbon-cycle processes. Nonlinear (including synergistic and antagonistic) effects among global change drivers were rare. Belowground carbon allocation responded negatively to increased precipitation and nitrogen addition and positively to decreased precipitation and elevated CO 2. The sensitivities of carbon variables to multiple global change drivers depended on the background climate and ecosystem condition, suggesting that Earth system models should be evaluated using site-specific conditions for best uses of this large dataset. Together, this synthesis underscores an urgent need to explore the interactions among multiple global change drivers in underrepresented regions such as semi-arid ecosystems, forests in the tropics and subtropics, and Arctic tundra when forecasting future terrestrial carbon-climate feedback.

The correlation between the surface chemistry and electronic structure is studied for SrTi 1-x Fe x O 3 (STF), as a model perovskite system, to explain the impact of Sr segregation on the oxygen reduction activity of cathodes in solid oxide fuel cells. Dense thin films of SrTi 0.95 Fe 0.05 O 3 (STF5), SrTi 0.65 Fe 0.35 O 3 (STF35) and SrFeO 3 (STF100) were investigated using a coordinated combination of surface probes. Composition, chemical binding, and valence band structure analysis using angle-resolved x-ray photoelectron 10 spectroscopy showed that Sr enrichment increases on the STF film surfaces with increasing Fe content. In situ scanning tunnelling microscopy / spectroscopy results proved the important and detrimental impact of this cation segregation on the surface electronic structure at high temperature and in oxygen environment. While no apparent band gap was found on the STF5 surface due to defect states at 345 o C and 10 -3 mbar of oxygen, the surface band gap increased with Fe content, 2.5 ± 0.5 eV for STF35 and 3.6 ± 0.6 eV for 15 STF100, driven by a down-shift in energy of the valence band. This trend is opposite to the dependence of the bulk STF band gap on Fe fraction, and is attributed to the formation of a Sr-rich surface phase in the form of SrO x on the basis of the measured surface band structure. The results demonstrate that Sr segregation on STF can deteriorate oxygen reduction kinetics through two mechanisms -inhibition of electron transfer from bulk STF to oxygen species adsorbing onto the surface, and the smaller 20 concentration of oxygen vacancies available on the surface for incorporating oxygen into the lattice. IntroductionBecause of their high efficiency and fuel flexibility, solid oxide fuel cells (SOFCs) offer the potential to contribute significantly to a clean energy infrastructure 1, 2 . However, their high working 25 temperatures (>800 o C) impose challenges due to accelerated materials degradation and high cost. The lowering of the working temperature has, therefore, become a strong focus of research. 3 At reduced temperatures (<700 o C), slow Oxygen Reduction Reaction (ORR) kinetics at the cathode become a major barrier to 30 the implementation of high performance SOFCs. To rationally design new cathode materials with high ORR activity, it is necessary to understand the governing ORR mechanisms and identify key descriptors of the cathode materials that directly control ORR activity. The strength of oxygen adsorption and the 35 energy barriers to oxygen dissociation, reduction and incorporation are believed to be the processes that determine oxygen reduction activity on perovskite oxides. 4,5 The energetics of these processes depends, in part, on the cathode electronic structure. In transition metal catalysis, the d-40 band structure 6 is a well-established descriptor of ORR activity. However, the applicability of the d-band model to perovskite oxide SOFC cathodes is limited by their complex surface chemistry (an anion and two cation sublattices), the role of oxygen vacan...

Transition-metal dichalcogenides (TMDs) have emerged in recent years as a special group of two-dimensional materials and have attracted tremendous attention. Among these TMD materials, molybdenum disulfide (MoS) has shown promising applications in electronics, photonics, energy, and electrochemistry. In particular, the defects in MoS play an essential role in altering the electronic, magnetic, optical, and catalytic properties of MoS, presenting a useful way to engineer the performance of MoS. The mechanisms by which lattice defects affect the MoS properties are unsettled. In this work, we reveal systematically how lattice defects and substrate interface affect MoS electronic structure. We fabricated single-layer MoS by chemical vapor deposition and then transferred onto Au, single-layer graphene, hexagonal boron nitride, and CeO as substrates and created defects in MoS by ion irradiation. We assessed how these defects and substrates affect the electronic structure of MoS by performing X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, and scanning tunneling microscopy/spectroscopy measurements. Molecular dynamics and first-principles based simulations allowed us to conclude the predominant lattice defects upon ion irradiation and associate those with the experimentally obtained electronic structure. We found that the substrates can tune the electronic energy levels in MoS due to charge transfer at the interface. Furthermore, the reduction state of CeO as an oxide substrate affects the interface charge transfer with MoS. The irradiated MoS had a faster hydrogen evolution kinetics compared to the as-prepared MoS, demonstrating the concept of defect controlled reactivity in this phase. Our findings provide effective probes for energy band and defects in MoS and show the importance of defect engineering in tuning the functionalities of MoS and other TMDs in electronics, optoelectronics, and electrochemistry.

Transition metal oxides or (oxy)hydroxides have been intensively investigated as promising electrocatalysts for energy and environmental applications. Oxygen in the lattice was reported recently to actively participate in surface reactions. Herein, we report a sacrificial template-directed approach to synthesize Mo-doped NiFe (oxy)hydroxide with modulated oxygen activity as an enhanced electrocatalyst towards oxygen evolution reaction (OER). The obtained MoNiFe (oxy)hydroxide displays a high mass activity of 1910 A/gmetal at the overpotential of 300 mV. The combination of density functional theory calculations and advanced spectroscopy techniques suggests that the Mo dopant upshifts the O 2p band and weakens the metal-oxygen bond of NiFe (oxy)hydroxide, facilitating oxygen vacancy formation and shifting the reaction pathway for OER. Our results provide critical insights into the role of lattice oxygen in determining the activity of (oxy)hydroxides and demonstrate tuning oxygen activity as a promising approach for constructing highly active electrocatalysts.