Search

Chemical vapor deposition (CVD) is the most effective method for the synthesis of large-scale and high-quality graphene. However, the growth temperature of graphene is high, about 1000 °C, using conventional CVD, meaning that it is expensiveand thus limits the use of the material. The synthesis of CVD graphene at low temperatures(

The Linxia Basin in northwestern China lies topographically at the northeastern margin of the Tibetan Plateau and climatically at the western margin of the East Asian monsoon region, and bears abundant mammalian fossils with environmental significance on central Asian aridification and east Asian monsoon evolution. However, these mammals have not been precisely dated, hindering our ability to address the ecologic environment changes associated with the evolution of the Asian monsoon and multiple uplifts of the Tibetan Plateau. We present a detailed paleomagnetic study of a sedimentary sequence from the Laogou section in the Linxia Basin containing many mammalian fossils with ages ranging between middle and late Miocene. The 203 m thick section revealed 11 normal and 10 reversed zones that correlate well with chrons 3An to 5An of the Geomagnetic Polarity Time Scale, constraining its age to ~12.56–6.0 Ma, and suggesting that the middle Miocene Platybelodon fauna existed at about 11.5 Ma and the late Miocene Hipparion fauna occurred at about 6.4 Ma. These ages, combined with other magnetostratigraphic results from the whole basin, show that these two major mammal faunas lived during 12.5–11.1 Ma and 11.5–6.3 Ma in the Linxia Basin. The presence of well-developed floodplain paleosols, the color change of the fluviolacustrine sediments and the transition of large bodied mammals suggest that strong climatic and environmental changes happened in the Linxia Basin during late – middle Miocene, in the form of a transition from the warm and humid forest to the warm and subarid steppe at about 11.1 Ma.

Supported platinum (Pt) catalysts present excellent chemoselectivity for a variety of hydrogenation reactions. Minimizing the use of such expensive catalysts while retaining their catalytic activities has been one of the most challenging topics in recent years. The construction of well dispersed, stable Pt single atom catalysts both increases the density of catalytically active sites while reducing Pt usage. Here we report the synthesis of Pt single atoms trapped in carbon onion graphitic shells by arc-discharge in aqueous solution. Such graphitic shells not only limit the chemical/thermal coarsening of Pt single atoms, but also enhance the conductivity for accelerating the penetration and exchange of ions and electrons during the catalytic process. Experimental results demonstrate that the Pt single atom catalysts show superior performance and no detectable loss of activity and selectivity over 10 cycles (both remain >99%) for the hydrogenation of p-chloronitrobenzene. This novel atomically dispersed form of Pt catalyst is indicative of a new avenue towards efficient synthesis of single atom catalysts with improved performance.

Two typical residential solar hot water engineering cases located in Chifeng and Tianjin are tested respectively. From the point of energy balance, a total of four parts of energy are calculated for the heat gain of heat collecting system, auxiliary energy consumption, and system heat loss, heat consumption of end users. It finds that solar fraction as an important reference index of the system design has certain limitations when evaluating the actual running system. In order to conduct a more comprehensive assessment of the actual energy-saving efficiency of solar hot water systems, three new kinds of evaluation index are put forward, which are solar energy utilization ratio, efficient replacement rate of fuel energy and system heat loss ratio.

Solar fraction is an important index to evaluate the energy saving effect of solar hot water system. However, the practical operation indicates that it has some limitations and fails to achieved anticipate result of energy saving if use it only. Therefore, the centralized solar hot water system of residential area in Tianjin is studied, the mathematical model of the heat-collecting unit, heat-supply unit and heat-using unit were established, and the mathematical model of the whole system is formed. MATLAB language was used to write the calculation procedures based on the above model, providing support for the research of system optimization and performance. And the performance index of the system is applied to simulated calculation. Based on the results of the simulation, the system performance in the whole-year, the effect of water consumption and the control strategies on the operation performance of this system are studied. Four parameters, solar fraction, solar energy utilization, efficient replacement ratio of foil energy, system heat dissipation ratio has been proposed as system performance evaluating index, and the strategy of reducing the water cycling time properly is put forward.

The electrocatalytic performance of the carbon supported catalysts can be effectively influenced by controlling the atomic structure of carbon materials. Herein, novel graphene nanospheres (GNs) composed of graphene nanoflakes are prepared through a modified arc-discharge method using toluene as carbon source. It is explored that these GNs possess high density of lattice disorder as well as the oxygen-containing functional groups. Attributing to the structural features, the Pt nanoparticles deposited on the prepared GNs exhibit a homogeneous dispersion without obvious aggregation. Such electrocatalyst with a Pt loading of 14.7 wt.% displays remarkable performance with low overpotentials of approximately −25 and −44 mV at the current density of −10 and −100 mA cm−2 as well as excellent cycling stability for the hydrogen evolution reaction. Thus, our result provides a suggestive way to improve the catalytic performance of the supported catalysts.

Metal single atom catalysts (SACs) have been attracting increasing attention in recent years owing to their incredible performance in several key catalytic reactions such as the oxygen reduction reaction and CO oxidation. The construction of well dispersed stable SACs can not only make it possible to understand the catalytic reactions on the atomic scale, but is also important for developing novel industrial catalysts. Recent efforts have been focused on dispersing metal SACs on carbon substrates rather than on metals or metal oxides for improved catalytic behavior. Especially, graphene-based materials have proven to be excellent candidates for supporting SACs due to their unique structural and electronic properties. Nevertheless, the anchoring mechanism between metal SACs and carbon substrates is not well understood. Here we review the many roles of carbon materials as the support of SACs and highlight the anchoring mechanism. We also propose some suggestions to improve the experimental and theoretical research methods to expand the number of applications and realize industrial applications.

The clean and renewable energy carrier alternative to current fossil fuels, such as hydrogen (H2) and oxygen (O2), is crucial and challenging due to economic and environmental concerns. Electrochemical water splitting is a straightforward route to produce H2 and O2, which requires highly active electrocatalysts to get over sluggish reaction kinetics and improve the reaction rates of H2 and O2 at low overpotentials. Transition metal borides (TMBs) have been proven as promising alternatives to replace precious metal catalysts. Here, we focus on the various synthetic strategies for the construction and functionalization of TMBs, then introduce the recent research progresses of TMBs for oxygen evolution reaction (OER). Finally, the existing problems in current research and future research directions of electrocatalysts are given as perspectives.