Nanocomposites CoPt-x/Diatomite-C as oxygen reversible electrocatalysts for zinc-air batteries: Diatomite boosted the catalytic activity and durability

The exploration of oxygen reversible electrocatalysts to boost oxygen reduction reaction and oxygen evolution reaction is critical for the development of high-performance aqueous Zn-air batteries. Since diatomite with porous structure can adsorb metal ions in aqueous solution, herein, we prepare the nanocomposite CoPt-x/Diatomite-C for both oxygen reduction and evolution reactions, and diatomite is found significantly promotes the electrocatalytic activity and durability. With the presence of diatomite, CoPt-1/Diatomite-C shows a lower Tafel slope (63 mV dec(-1) at high potential range), larger diffusion-limited current density (4.94 mA cm(-2)) and superior durability for ORR. Particularly, the specific and mass activities of CoPt-1/Diatomite-C for ORR are 0.74 mA cm(-2) and 286 mA mg(-1), respectively, which are 2.5 and 3.0 times higher than that of CoPt-1/C without diatomite; For OER, the overpotential of CoPt-9/Diatomite-C decreases nearly 30 mV at 10 mA cm(-2), while the Tafel slope also reduces 16 mV dec(-1) versus CoPt-9/C catalyst. Moreover, a rechargeable Zn-air battery with these composites as air-cathode is self-assembled, and diatomite boosts the battery performance with desirable properties. CoPt-9/Diatomite-C displays the optimal performance, with a power density of 140 mW cm(-2), a specific capacity of 616 mA h g(-1) at 10 mA cm(-2) and an exceedingly robust cycling life. This work provides a viable and cost-effective strategy for fabricating oxygen reversible electrocatalysts for metal-air battery applications. (C) 2018 Elsevier Ltd. All rights reserved

A late Quaternary planktonic foraminifer faunal record of rapid climatic changes of sediment core GIK17938-2

A high-resolution planktonic foraminifer record from a core recovered from the South China Sea (SCS) (Sonne 17938-2: 19°47.2'N, 117° 32.3E; 2840 m; Delta t c. 250-1000 years) shows rapid millennial-scale changes in the western Pacific marginal sea climate during the last 30,000 years. The SCS is the largest western Pacific marginal sea off the southeast Asian continent, the area today dominated by seasonal monsoon changes. Quantitative analyses of planktonic foraminifer faunal abundance data frorn the core indicate large downcore variations in the relative abundances of the dominant taxa since about 30,000 years ago in the isotope stage 3. Further analyses indicate that the abundance of G. inflata, a good indicator species for cold SST (~13°-19°C) and deep MLD (~100-125 m) waters shows abrupt shifts. During stages 2 and 3, the abundance record of G. infiata tends to be punctuated by quasi-periodie short intervals (~2000-3000 yrs) where its abundance reaches 15% or greater, superimposed on generally low (5-10%) background values. This pattern suggests an instability of surface ocean conditions of the SCS during the past 30,000 years. The abrupt abundance changes of G. infiata correlate well with similar climatic changes observed from a GISP2 ice core 8180, and North Atlantic core DSDP 609 N. pachyderma (s.) and lithic grain abundances during 'Heinrich evcnts'. These results suggest that the millennial-scale variability of climate is not peculiar to the Atlantic region. Apparently, the rapid SCS climatic changes during Heinrich events are driven by effective mechanisms, of particularly the effects of shifts in the latitudinal position of the Siberia High Pressure System