Towards the rational design of Pt-based alloy catalysts for the low-temperature water-gas shift reaction: from extended surfaces to single atom alloys

The rational design of Pt-based catalysts for the low-temperature water-gas-shift (LT-WGS) reaction is an active research field because of its important role played in the fuel cell-based hydrogen economy, especially in mobile applications. Previous theoretical analyses have suggested that Pt alloys, leading to a weaker CO binding affinity than the Pt metal, could help alleviate CO poisoning and thus should be promising catalysts of the LT-WGS reaction. However, experimental research along this line was rather ineffective in the past decade. In the present work, we employed the state-of-the-art kinetic Monte Carlo (KMC) simulations to examine the influences of the electronic effect by introducing sub-surface alloys and/or core–shell structures, and the synergetic effect by introducing single atom alloys on the catalytic performance of Pt-alloy catalysts. Our KMC simulations have highlighted the importance of the OH binding affinity on the catalyst surfaces to reduce the barrier of water dissociation as the rate determining step, instead of the CO binding affinity as has been emphasized before in conventional mean-field kinetic models. Along this new direction of catalyst design, we found that Pt–Ru synergetic effects can significantly increase the activity of the Pt metal, leading to Ru_1–3@Pt alloys with a tetrahedron site of one surface-three subsurface Ru atoms on the Pt host, showing a turnover frequency of about five orders of magnitude higher than the Pt metal.

KMC simulations show that decreasing the barrier of H₂O decomposition is more beneficial than decreasing the CO binding affinity in LT-WGS, while the latter was overemphasized by MF-MKM. Here Ru_1–3@Pt alloy is proposed as a promising catalyst.     

Sending-or-Not-Sending Twin-Field Quantum Key Distribution with a Passive Decoy-State Method

Twin-field quantum key distribution (TF-QKD) has attracted considerable attention because it can exceed the basic rate-distance limit without quantum repeaters. Its variant protocol, sending or not-sending quantum key distribution (SNS-QKD), not only fixes the security vulnerability of TF-QKD, but also can tolerate large misalignment errors. However, the current SNS-QKD protocol is based on the active decoy-state method, which may lead to side channel information leakage when multiple light intensities are modulated in practice. In this work, we propose a passive decoy-state SNS-QKD protocol to further enhance the security of SNS-QKD. Numerical simulation results show that the protocol not only improves the security in source, but also retains the advantages of tolerating large misalignment errors. Therefore, it may provide further guidance for the practical application of SNS-QKD.     

分光计测定光栅常数

针对分光计测定光栅常数实验中入射光线偏离光栅法线的情形,提出了计算光栅常数的一个近似表达式。在不增加额外测量的前提下,使实验结果更接近于实际值。     

NIR TADF emitters and OLEDs: challenges,progress, and perspectives

Near-infrared (NIR) light-emitting materials show excellent potential applications in the fields of military technology, bioimaging, optical communication, organic light-emitting diodes (OLEDs), etc. Recently, thermally activated delayed fluorescence (TADF) emitters have made historic developments in the field of OLEDs. These metal-free materials are more attractive because of efficient reverse intersystem crossing processes which result in promising high efficiencies in OLEDs. However, the development of NIR TADF emitters has progressed at a relatively slower pace which could be ascribed to the difficult promotion of external quantum efficiencies. Thus, increasing attention has been paid to NIR TADF emitters. In this review, the recent progress of NIR TADF emitters has been summarized along with their molecular design strategies and photophysical properties, as well as electroluminescence performance data of their OLEDs, respectively.

This review presents the recent progress of NIR TADF emitters along with their molecular design strategies and photophysical properties, as well as the electroluminescence performance data of the emitters and their OLEDs.     

相干光脉冲位置调制信道容量及传信率最大化研究

分析了相干光脉冲位置调制的信道容量及传信率最大化条件.通过分析光外差接收的脉冲位置调制信号具有的概率分布特性,推导出采用最大似然检测的相干脉冲位置调制信道具有的转移概率矩阵和信道容量,证明在检测器散粒噪声极限假设下,信道容量只取决于接收脉冲能量和脉冲位置调制阶数.利用Jensen不等式化简信道容量得到其下限,该下限能够近似实际通信链路的信道容量.基于此估计出达到最高传信率时的脉冲位置调制阶数同粒子数反转的重建时间之间的关系,给出了二者在一定范围内的一般映射.数值仿真表明,在接收能量使信道误码率优于10-2时,估箅出的脉冲位置调制阶数能够使传信率接近最大值.     

基于透明陶瓷材料的激光研究进展

陶瓷激光器是一种以透明陶瓷材料作为增益介质的激光器.与单晶相比,透明陶瓷具有制备周期短和烧结温度低等优势,在激活离子高掺杂浓度下能保证良好的光学均匀性,且容易制备成各种大尺寸复合结构.近年在高功率和超短超强激光输出方面得到广泛应用,产生了一系列研究成果.回顾了陶瓷激光器的发展历程,总结了透明陶瓷在高功率、超短超强脉冲激...     

近江牡蛎受精细胞学研究

用醋酸──地衣红染色的方法对近江牡蛎人工授精的卵子减数分裂和受精过程进行了详细的细胞学观察．精子入卵前，卵子处于第一次减数分裂的前期（胚泡期），精子入卵后，胚泡消失，然后进行两次减数分裂，在海水温度为２８．８℃的情况下，授精后３３ｍｉｎ和４５ｍｉｎ，绝大部分受精卵已排出第一极体和第二极体，雄原核可在第一极体排出后及第二极体排出前任何时期内形成，雌雄原核以联合的方式将两组染色体合并，授精后１ｈ，大部分卵子完成第一次卵裂．在２５℃和２６℃授精的情况下，观察到了较多的多精入卵的现象．卵子发育的非同步性现象非常明显．     

C波段加速器初步热测实验

为了开展加速器小型化技术研究,进行了C波段2 MeV驻波加速器研制工作。目前,该加速器研制取得了显著进展,完成了全密封加速管的焊接,建立了加速器热测实验平台。在重复频率50 Hz情况下,进行了初步热测出束实验,利用电离室剂量仪测试了加速器靶前1 m处的X射线剂量率,并利用钢吸收法测试了电子束的能量。初步实验结果表明:电子束能量约2.5 MeV,剂量率超过330 mGy/(minm)。     

Oscillation of coercivity between positive and negative in MnxGe1-x：H ferromagnetic semiconductor films

Amorphous MnxGe1-x :H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron cosputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x :H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6 :H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics.