DataSheet1_Carbon dioxide flux in the drained drawdown areas of Three Gorges Reservoir.doc

A huge amount of CO2 emissions from the drained drawdown areas of reservoirs overturns the previous results in carbon budget. Three Gorges Reservoir (TGR) has a large drawdown area, which accounts for nearly one third of the total area of the TGR. However, the total CO2 emissions from the TGR drawdown area have seldom been estimated by far. To demonstrate the contribution of CO2 emissions from the TGR drawdown areas, the study measured CO2 emissions from the downstream part of the TGR drawdown areas by the chamber method, and synthesized CO2 emissions from the other parts of TGR drawdown areas. Both the diel and seasonal variation indicated that CO2 emission fluxes were significantly higher in the drained season than in the flooded season. The average CO2 emission flux in the drained season was about 1.7 times higher than that in the inundated season in our experiments, and the ratio increased to 4.8 times when other available data was added. CO2 emission flux in the drained season was positively correlated with air temperature, soil temperature at 5 cm depth, soil water content, organic carbon, and soil nitrate nitrogen, but negatively correlated with elevations. CO2 emission from the TGR drawdown area was estimated to be 342.67–495.96 Gg yr−1 in the drained season, and offset about 80% of carbon fixation by vegetation in the TGR drawdown area. Therefore, CO2 emission from the drained soils should be included in the carbon budget of reservoir systems, especially for these reservoirs with a large drawdown area.</p

Hydrogen-triggered metal filament rupture in Cu-based resistance switches

Cation-based resistance switches have been considered as promising candidates for memory cells and other novel devices. So far, the most accepted switching processes of such devices are based on the formation/rupture of metallic filaments between two electrodes. Although many recent studies have identified the existence of H2O (and resulting -OH groups) in such devices, their effects on the switching process are still unclear. In the present work, by taking Cu/Ta2O5/Pt device as an example, we have theoretically revealed that H ions may dissociate from -OH groups and accumulate onto the Cu filament in amorphous Ta2O5. After that, the adsorbed H ions will induce a series of changes, such as the elongation of the adjacent Cu-Cu bonds, the weakening of the Cu-Cu bonds, the increase of charge on Cu cations, and the enhancement of diffusivities of Cu cations, all of which eventually lead to the rupture of the Cu filament. Interestingly, our proposed ‘H-triggered metal filament rupture’ model is similar to the widely studied ‘hydrogen embrittlement phenomenon’. The crucial point of this model is the high catalytic activity of Cu towards the splitting of -OH group. Consequently, it is expected that this model could be applicable to other Cu-cation based resistance switches. Cation-based resistance switches have been considered as the promising candidates for memory cells and other novel devices. So far, the most accepted switching processes of such devices are based on the forming/rupture of metallic filaments between two electrodes. Although many recent studies have identified the existence of H2O (and as-resulted -OH groups) in such devices, their effects on the switching process are still unclear. In the present work, by taking Cu/Ta2O5/Pt device as an example, we have theoretically proposed that the H ions take the very important role during the rupture process of Cu filament in such device. Interestingly, our proposed ‘H-triggered metal filament rupture’ model is similar to the widely studied ‘Hydrogen Embrittlement’ phenomenon in the industry field, which serves as additional evidence supporting the credibility of such model. The crucial point of mechanism of this model is considered to be the high catalytic activity of Cu towards the splitting of -OH group. Consequently, it is expected that this model could be applicable to other Cu-cation based resistance switches.</p

Metal-Doped C₃B Monolayer as the Promising Electrocatalyst for Hydrogen/Oxygen Evolution Reaction: A Combined Density Functional Theory and Machine Learning Study

The development of high-efficiency electrocatalysts for hydrogen evolution reduction (HER)/oxygen evolution reduction (OER) is highly desirable. In particular, metal borides have attracted much attention because of their excellent performances. In this study, we designed a series of metal borides by doping of a transition metal (TM) in a C3B monolayer and further explored their potential applications for HER/OER via density functional theory (DFT) calculations and machine learning (ML) analysis. Our results revealed that the |ΔG*H| values of Fe-, Ag-, Re-, and Ir-doped C3B are approximately 0.00 eV, indicating their excellent HER performances. On the other hand, among all the considered TM atoms, the Ni- and Pt-doped C3B exhibit excellent OER activities with the overpotentials smaller than 0.44 V. Together with their low overpotentials for HER (3B and Pt/C3B could be the potential bifunctional electrocatalysts for water splitting. In addition, the ML method was employed to identify the important factors to affect the performance of the TM/C3B electrocatalyst. Interestingly, the results showed that the OER performance is closely related to the inherent properties of TM atoms, i.e., the number of d electrons, electronegativity, atomic radius, and first ionization energy; all these values could be directly obtained without DFT calculations. Our results not only proposed several promising electrocatalysts for HER/OER but also suggested a guidance to design the potential TM–boron (TM–B)-based electrocatalysts