Biphase Pd Nanosheets with Atomic-Hybrid RhOx/Pd Amorphous Skins Disentangle the Activity-Stability Trade-Off in Oxygen Reduction Reaction.

The activity-stability trade-off relationship of oxygen reduction reaction (ORR) is a tricky issue that strikes the electrocatalyst population and hinders the widespread application of fuel cells. Here neoteric biphase Pd nanosheets that are structured with ultrathin two-dimensional crystalline Pd inner cores and ≈1 nm thin atomic-hybrid RhOx/Pd amorphous skins, named c/a-Pd@PdRh NSs, for disentangling this trade-off dilemma for alkaline ORR are developed. The superthin amorphous skins significantly amplify the quantity of flexibly low-coordinated atoms for electrocatalysis. An in situ selected oxidation of the top-surface Rh dopants creates atomically hybrid RhOx/Pd disorder surfaces. Detailed energy spectra and theoretical simulation confirm that these RhOx/Pd interfaces can arouse a surface charge redistribution, causing significant electron deficiency and lowered d-band center for surface Pd. Meanwhile, anticorrosive Rh/RhOx species can thermodynamically passivate the neighboring Pd atoms from oxidative dissolution. Thanks to these amplified interfacial effects, the biphase c/a-Pd@PdRh NSs simultaneously exhibit a superhigh ORR activity (5.92 A mg-1, 22.8 times that of Pt/C) and an outstanding long-lasting stability after 100k cycles of accelerated durability test, showcasing unprecedented electrocatalysts for breaking the activity-stability trade-off relationship of ORR. This work paves a bran-new strategy for designing high-performance electrocatalysts through creating modulated amorphous skins on low-dimensional nanomaterials.

Breaking Surface Atomic Monogeneity of Rh2 P Nanocatalysts by Defect-Derived Phosphorus Vacancies for Efficient Alkaline Hydrogen Oxidation.

Breaking atomic monogeneity of catalyst surfaces is promising for constructing synergistic active centers to cope with complex multi-step catalytic reactions. Here, we report a defect-derived strategy for creating surface phosphorous vacancies (P-vacancies) on nanometric Rh2 P electrocatalysts toward drastically boosted electrocatalysis for alkaline hydrogen oxidation reaction (HOR). This strategy disrupts the monogeneity and atomic regularity of the thermodynamically stable P-terminated surfaces. Density functional theory calculations initially verify that the competitive adsorption behavior of Had and OHad on perfect P-terminated Rh2 P{200} facets (p-Rh2 P) can be bypassed on defective Rh2 P{200} surfaces (d-Rh2 P). The P-vacancies enable the exposure of sub-surface Rh atoms to act as exclusive H adsorption sites. Therein, the Had cooperates with the OHad on the peripheral P-sites to effectively accelerate the alkaline HOR. Defective Rh2 P nanowires (d-Rh2 P NWs) and perfect Rh2 P nanocubes (p-Rh2 P NCs) are then elaborately synthesized to experimentally represent the d-Rh2 P and p-Rh2 P catalytic surfaces. As expected, the P-vacancy-enriched d-Rh2 P NWs catalyst exhibits extremely high catalytic activity and outstanding CO tolerance for alkaline HOR electrocatalysis, attaining 5.7 and 14.3 times mass activity that of p-Rh2 P NCs and commercial Pt/C, respectively. This work sheds light on breaking the surface atomic monogeneity for the development of efficient heterogeneous catalysts.

Two-dimensional template-directed synthesis of one-dimensional kink-rich Pd3Pb nanowires for efficient oxygen reduction.

Developing facile synthetic strategies toward ultrafine one-dimensional (1D) nanowires (NWs) with rich catalytic hot spots is pivotal for exploring effective heterogeneous catalysts. Herein, we demonstrate a two-dimensional (2D) template-directed strategy for synthesizing 1D kink-rich Pd3Pb NWs with abundant grain boundaries to serve as high-efficiency electrocatalysts toward oxygen reduction reaction (ORR). In this one-pot synthesis, ultrathin Pd nanosheets were initially generated, which then served as self-sacrificial 2D nano-templates. A dynamic equilibrium growth was subsequently established on the 2D Pd nanosheets through the center-selected etching of Pd atoms and edge-preferred co-deposition of Pd/Pb atoms. This was followed by the oriented attachment of the generated Pd/Pb alloy nanograins and fragments. Thus, kink-rich Pd3Pb NWs with rich grain boundary defects were obtained in high yield, and these NWs were used as electrocatalytic active catalysts. The surface electronic interaction between Pd and Pb atoms effectively decreased the surface d-band center to weaken the binding of oxygen-containing intermediates toward improved ORR kinetics. Specifically, the kink-rich Pd3Pb NWs/C catalyst delivered outstanding ORR mass activity and specific activity (2.26 A⋅mgPd-1 and 2.59 mA⋅cm-2, respectively) in an alkaline solution. These values were respectively 13.3 and 10.8 times those of state-of-the-art commercial Pt/C catalyst. This study provides an innovative strategy for fabricating defect-rich low-dimensional nanocatalysts for efficient energy conversion catalysis.

Equilibrated PtIr/IrOx Atomic Heterojunctions on Ultrafine 1D Nanowires Enable Superior Dual-Electrocatalysis for Overall Water Splitting.

Dual-active-sites atomically coupled on ultrafine 1D nanowires (NWs) can offer synergic atomic heterojunctions (AHJs) and high atomic-utilization toward multipurpose and superior catalysis. Here, ≈2-nm-thick PtIr/IrOx hybrid NWs are elaborately synthesized with equilibrated Pt/IrOx AHJs as high-efficiency bifunctional electrocatalysts for overall water splitting. Mechanism studies reveal the atomically coupled Pt-IrOx dual-sites are favorable for facilitating water dissociation, alleviating the binding of H* on Pt sites and inversely regulating the *OH adsorption and oxidation on bridge Ir-Ir sites. By simply equilibrating the Pt-IrOx ratio, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be substantially accelerated. In particular, Pt-rich PtIr/IrOx -30 NWs attain 11-fold enhancements for HER compared to Pt/C in 1.0 m KOH, while IrOx -rich PtIr/IrOx -50 NWs express about five times mass activity referring to Ir/C for OER. Remarkably, the ratio-optimized PtIr/IrOx NWs electrode couple achieves a durably continuous H2 production under a substantially low cell voltage.

Characterizing the long-term occurrence of polycyclic aromatic hydrocarbons and their driving forces in surface waters.

As carcinogenic and ubiquitous pollutants, an in-depth understanding of the long-term environmental behaviors of polycyclic aromatic hydrocarbons (PAHs) and their driving forces is crucial for reducing human health risks. Based on long-term monitoring data from 2001 to 2016, this study systematically investigated the temporal and seasonal trends, periodic oscillation, source apportionment, and human health risks of PAHs in eight rivers in the Free State of Saxony, Germany. The results showed that the annual average ∑16PAHs (sum of 16 PAH concentrations) ranged from 28.2 ng L-1 to 202 ng L-1. Using the Mann-Kendall test, a trend of decreasing PAH concentrations was determined (slope range: -0.103 to -0.0159). Wavelet analysis indicated that the most significant periodic oscillation of PAHs was 10-30 months, with more pollution in winter. Source apportionment analysis suggested that vehicular emissions and coal combustion contributed the most to PAH concentrations (20.6-40.3% and 21.7-41.4%, respectively) and related health risks (54.1-80.1% and 5.61-37.9%, respectively). Furthermore, the risks (oral lifetime: 4.24×10-7-1.34×10-6; dermal lifetime: 2.86×10-5-9.05×10-5) were determined to be low. The data revealed that the substitution of petroleum and coal with cleaner energy would facilitate the mitigation of PAHs.

[Potential Source Contribution Analysis of the Particulate Matters in Shanghai During the Heavy Haze Episode in Eastern and Middle China in December, 2013].

A heavy haze pollution episode occurred in early December, 2013 in middle and eastern China, which lasted for a long period, and covered a large area. During this episode, the hourly maximum concentrations of PM10 and PM2.5 in Shanghai exceeded 700 µg.m-3 and 600 µg.m-3, respectively. To obtain the major air mass transportation path, trajectories reaching urban Shanghai area were analyzed using HYSPLIT model and cluster analysis. Potential Source Contribution Function (PSCF) and Concentration-Weighted Trajectory (CWT) methods were applied to study the potential source regions and the individual contributions to PM10 in Shanghai in December, 2013. The results showed that the northwest and the north paths were the major air mass transport paths in December, among which 79. 6% of the total trajectories came from mainland, while 20. 4% reached Shanghai through the ocean. These were the main transportation paths causing high PM10 mass concentration in December in Shanghai. The potential regions affecting the heavy haze episode in early December in Shanghai were distributed in the Yangtze River Delta including Jiangsu, Zhejiang and Anhui. Besides, air mass from Shandong, Hebei and Henan also had certain impact. The results showed that regional and even super-regional pollution joint control was of significant importance to reduce the frequent heavy air pollution episodes.