Fe–N–C materials exhibit excellent activity and stability for oxygen reduction reaction (ORR), as one of the most promising candidates to replace commercial Pt/C catalysts. However, it is challenging to unravel features of the superior ORR activity originating from Fe–N–C materials. In this work, the electronic and geometric structures of the isolated Fe–N–C sites and their correlations with the ORR performance are investigated by varying the secondary thermal activation temperature of a rationally designed NC‐supported Fe single‐atom catalyst (SAC). The systematic analyses demonstrate the significant role of coordinated atoms of SA and metallic Fe nanoparticles (NPs) in altering the electronic structure of isolated Fe–N–C sites. Meanwhile, strong interaction between isolated Fe–N–C sites and adjacent Fe NPs can change the geometric structure of isolated Fe–N–C sites. Theoretical calculations reveal that optimal regulation of the electronic and geometric structure of isolated Fe–N–C sites by the co‐existence of Fe NPs narrows the energy barriers of the rate‐limiting steps of ORR, resulting in outstanding ORR performance. This work not only provides the fundamental understanding of the underlying structure–activity relationship, but also sheds light on designing efficient Fe–N–C catalysts.

This study focuses on the chemical composition, and the factors controlling it, of the high mountain-rivers in the source region of the Yangtze River on the Tibetan Plateau. By comprehensive and systematic analysis, the chemical signatures, spatial variations of water quality, as well as the factors controlling them are studied. The value of the average total dissolved solids (TDS) is 778 mg/l, ranging from 117 to 5496 mg/l. In order of decreasing concentration, the main cations are Na try of the river water is controlled by lithogenic weathering processes. The Na-normalized ratio end-member diagram indicates that the weathering of silicates and carbonates is relatively significant, on the whole. There exists pronounced regional heterogeneity in the water chemistry and the factors affecting it. The northern rivers, including Chumaer He, Beilu He, and Ranchiqu, are mainly affected by evaporation and crystallization processes, while the southern rivers (Tuotuo He, Gaerqu, and Buqu) show effects from the weathering of carbonates and silicates.

As a two-dimensional direct band gap semiconductor with unique electronic and magnetic properties, monolayer chromium triiodide (CrI3) has a great potential for spintronic applications. Under the guidance of the defect theory, we adopt first-principles calculation to determine the structural, thermodynamic, electronic, and magnetic properties of point defects of monolayer CrI3. Twenty kinds of point defects, including vacancies, interstitial, substitution, and bond-rotation defects have been investigated. Either the metalloid or metallic single atom vacancies is energetically stable depends on the chemical potential of iodide, leading to the intrinsic n-type and p-type dopings, respectively. More interestingly, a ferromagnetic to antiferromagnetic transition of the magnetic phase can be induced for most type of point defects, which can be explained by a simple Heisenberg model. The content of present investigation contributes to the atomic-scale understanding of the electric and magnetic properties of monolayer CrI3.

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In this study, a novel flame retardant (PMrG) was developed by self-assembling melamine and phytic acid (PA) onto rGO, and then applying it to the improvement of the flame resistance of PLA. PMrG simultaneously decreases the peak heat release rate (pHRR) and the total heat release (THR) of the composite during combustion, and enhances the LOI value and the time to ignition (TTI), thus significantly improving the flame retardancy of the composite. The flame retardant mechanism of the PMrG is also investigated. On one hand, the dehydration of PA and the decomposition of melamine in PMrG generate non-flammable volatiles, such as H2O and NH3, which dilute the oxygen concentration around the combustion front of the composite. On the other hand, the rGO, melamine, and PA components in PMrG create a synergistic effect in promoting the formation of a compact char layer during the combustion, which plays a barrier role and effectively suppresses the release of heat and smoke. In addition, the PMrGs in PLA exert a positive effect on the crystallization of the PLA matrix, thus playing the role of nucleation agent.