Science Bulletin最新文献

Almost all of Cu_xS compounds only produce the simple two-electron transferred products CO and HCOOH but it remains a large challenge to obtain the multiple-electron transferred hydrocarbon products in electrocatalytic CO₂ reduction reaction (CO₂RR). Moreover, identifying the distinct contributions of S atoms to catalysis, particularly for catalytic activity and product selectivity in electrocatalytic CO₂RR, remains a challenging task. Herein, we introduce a model catalyst based on a conductive two-dimensional metal-organic framework with defined Cu-S₄ active sites, named Cu₃(THT)₂ (THT = 2,3,6,7,10,11-hexathiotriphenylene) for CO₂RR. Unlike the precursor catalyst Cu₃(HITP)₂ with Cu-N₄ motifs that predominantly produce common two-electron transferred product CO (40% selectivity), Cu₃(THT)₂ shifts the primary product to deep reduction product CH₄. At -1.4 V versus the reversible hydrogen electrode (RHE), Cu₃(THT)₂ achieves a Faradaic efficiency of 63.5% for CH₄ and the current density reaches a high value of -298.3 mA cm^-2. Theoretical studies indicate that the electron-rich Cu-S₄ sites stabilize and activate the key intermediate *CO more effectively than Cu-N₄ sites. Furthermore, S atoms can accept electrons and form weak S···O interactions with *CO, providing additional stabilization for *CO. This study is the first to show that non-metallic S centers around catalytic metal sites can significantly enhance and tune product selectivity in CO₂RR.

The tropopause chemical structure (TCS) is influenced by stratosphere-troposphere exchange (STE) and plays a role in the Earth's climate. However, this role is still not fully understood in East Asia, where active STE and high anthropogenic emissions coexist. Using airborne measurements of trace gases, including O₃, CO, and H₂O, we reveal the variations in TCS during two consecutive cut-off lows (COLs), an important trigger of STE. We demonstrate the important roles of two-way STE and long-range transport processes in delivering natural and anthropogenic signatures in the TCS. The former COL case shows a normal pattern of TCS, consisting of stratospheric and tropospheric air and a mixture of them. The latter, as a novel type of STE, exhibits an anomalous and complex structure due to deep convective injection into stratospheric intrusions and advection of remote marine air. The distinct mixture of stratospheric air and anthropogenic pollution alters the TCS, with horizontal and vertical scales estimated to be 200 and 1 km, respectively. Moreover, air of maritime origin, which is convectively transported and strongly dehydrated during long-range transport, is also identified. Such a complex TCS can produce unique chemical environments that modulate cloud physics and atmospheric radiation. From a climatological perspective, events of these anomalous airmasses are nonnegligible in terms of their frequency and chemical impact, as revealed by multiyear observations. These new insights advance our understanding of the mixing of natural and anthropogenic species that shape the TCS in East Asia and have implications for climate change.

Clouds significantly influence the Earth's energy budget, typically exerting a net global cooling effect by balancing shortwave radiation shading and longwave radiation trapping. However, here we report a shortwave warming effect by clouds over Greenland, contrary to the conventional belief of a cooling effect. We find that the shortwave cloud warming effect on the Earth-atmosphere system is particularly prominent for optically thin clouds. Utilizing satellite-based observations over Greenland during the summer season from 2013 to 2022, we identify a positive shortwave cloud radiative effect when the ratio of surface albedo to top-of-atmosphere (TOA) reflectivity reaches a critical threshold, implying that cloud-induced warming can occur in any place when the surface is bright enough compared with TOA. The shortwave warming effect (with radiative effect up to 25 W/m²) over Greenland is primarily concentrated in the peripheries and southern margins-regions experiencing the most intense ice melt. From a global perspective, these warming clouds can contribute up to 0.36 W/m² to the summer Earth-atmosphere system in the Northern Hemisphere. These findings are critical for understanding the radiation budget in the polar regions, improving predictions of polar ice melt, and enhancing our comprehension of the Earth's energy budget.