Promoting electrocatalytic CO2 reduction to formate via sulfur-boosting water activation on indium surfaces

一般认为，H2O还原析氢反应是CO2还原反应的竞争反应，若促进H2O活化将降低CO2还原反应的法拉第效率。因此，基于该认识设计出的高CO2还原法拉第效率的催化剂常常活性低。王野课题组打破这种认识，提出H2O分子活化在CO2还原中起着重要的作用，成功合成出硫修饰In催化剂来活化H2O分子而促进CO2还原制甲酸的新方法，该催化剂在非常宽的电流密度范围内（25~100 mA cm-2），均可以维持85%以上的甲酸法拉第效率。将硫拓展至硒和碲等其它硫族元素以及将金属铟拓展至铋和锡等其它p区金属，均实现很好的促进效果，表明通过促进水的活化来提高CO2电催化还原性能具有普适性。该工作为理性设计高效的CO2还原电催化剂提供了新策略。 该研究工作实验部分主要由王野、张庆红教授指导，能源材料化学协同创新中心iChEM2016级博士生马文超、固体表面物理化学国家重点实验室高级工程师谢顺吉（共同第一作者）完成；理论计算部分由吴德印教授指导，2015级博士生张霞光（共同第一作者）完成。醇醚酯国家工程实验室高级工程师康金灿参与了部分实验表征。上海光源姜政教授和孙凡飞博士为同步辐射表征提供了支持。【Abstract】Electrocatalytic reduction of CO2 to fuels and chemicals is one of the most attractive routes for CO2 utilization. Current catalysts suffer from low faradaic efficiency of a CO2-reduction product at high current density (or reaction rate). Here, we report that a sulfur-doped indium catalyst exhibits high faradaic efficiency of formate (>85%) in a broad range of current density (25–100 mA cm−2) for electrocatalytic CO2 reduction in aqueous media. The formation rate of formate reaches 1449 μmol h−1 cm−2 with 93% faradaic efficiency, the highest value reported to date. Our studies suggest that sulfur accelerates CO2 reduction by a unique mechanism. Sulfur enhances the activation of water, forming hydrogen species that can readily react with CO2 to produce formate. The promoting effect of chalcogen modifiers can be extended to other metal catalysts. This work offers a simple and useful strategy for designing both active and selective electrocatalysts for CO2This work was supported by the National Key Research and Development Program of the Ministry of Science and Technology of China (No. 2017YFB0602201), the National Natural Science Foundation of China (Nos. 21690082, 91545203, and 21503176). We thank staff at the BL14W1 beamline of the Shanghai Synchrotron Radiation Facilities (SSRF) for assistance with the EXAFS measurements. 研究工作得到科技部重点研发计划（批准号：2017YFB0602201）和国家自然科学基金（批准号：21690082、91545203、21503176）等项目的资助

Electrocatalytic reduction of CO2 to ethylene and ethanol through hydrogen-assisted C-C coupling over fluorine-modified copper

精准控制C1分子C-C偶联合成特定C2+化合物是C1化学中极具挑战性的难题。由于C2+化合物(如乙烯和乙醇)在化工和能源领域具有重要用途，将CO2直接转化为C2+产物极具吸引力。发展高效催化剂，实现高电流密度、高C2+选择性、高稳定性的“三高”性能，是推进电催化还原CO2走向实际应用的关键。研究团队针对电催化还原CO2中高CO2还原法拉第效率的催化剂常常活性低的问题，提出了适当提高催化剂活化水的能力对增加CO2还原活性的重要性，发展出氢助碳碳偶联(hydrogen-assisted C-C coupling)的新策略，在氟修饰的铜(F-Cu)催化剂上实现了CO2电催化还原制乙烯和乙醇的新突破。该研究工作实验部分主要由王野、张庆红教授指导，能源材料协同创新中心iChEM2016级博士生马文超、固体表面物理化学国家重点实验室高级工程师谢顺吉(共同第一作者)完成；理论计算部分由程俊教授指导，2017级硕士生刘彤彤(共同第一作者)、2016级博士生樊祺源完成。叶进裕博士为原位红外测试提供了支持。上海光源姜政研究员、孙凡飞博士、杨若欧为同步辐射表征提供了支持。 这是投稿的最终版本，正式出版的论文版本请访问官方链接（https://doi.org/10.1038/s41929-020-0450-0）。Electrocatalytic reduction of CO2 into multi-carbon (C2+) products is a highly attractive route for CO2 utilization. However, the yield of C2+ products remains low because of the limited C2+ selectivity at high CO2 conversion rate. Here, we report a fluorine-modified copper catalyst that exhibits an ultrahigh current density of 1.6 A cm−2 at C2+ (mainly ethylene and ethanol) Faradaic efficiency of 80% for electrocatalytic CO2 reduction in a flow cell. The C2-4 selectivity reaches 85.8% at a single-pass yield of 16.5%. We show a hydrogen-assisted C−C coupling mechanism between adsorbed formyl (CHO) intermediates for C2+ formation. Fluorine enhances water activation, CO adsorption and hydrogenation of adsorbed CO to CHO intermediate that can readily undergo coupling. Our findings offer an opportunity to design highly active and selective CO2 electroreduction catalysts with potential for practical applicationThis work was supported by the National Key Research and Development Program of the Ministry of Science and Technology of China (No. 2017YFB0602201), the National Natural Science Foundation of China (Nos. 21690082, 91545203, 21503176 and 21802110), We thank staffs at the BL14W1 beamline of the Shanghai Synchrotron Radiation Facilities (SSRF) for assistance with the EXAFS measurements.研究工作得到科技部重点研发计划（批准号：2017YFB0602201）和国家自然科学基金（批准号：21690082、91545203、21503176、21802110）项目的资助

Research on Relay Node Placement in Industrial Wireless Sensor networks

无线传感器网络（Wireless Sensor Network, WSN）的出现加速了物理世界与虚拟信息世界融合的实现，并深刻改变着人类感知世界的方式，使其成为继互联网后，又一引领信息产业革命的热点技术。随着WSN大范围的应用，WSN以其低成本、安装方便和易维护等优点，正逐步应用于多种工业场景中。工业无线传感器网络（Industrial Wireless Sensor Network, IWSN）已成为降低测控系统成本，扩展其应用范畴的革命性技术。多数工业应用场景中，传感器节点位置已知且固定，然而这些低成本节点具有通信范围小、能量受限等缺陷，须通过部署额外的中继节点保证网络连通性。虽然近年来各国学者对WSN中继节点部署问题进行了广泛而深入地研究，但特别针对IWSN中继节点部署问题的研究尚处于起步阶段。 不同于传统应用，工业应用具有大规模、低功耗、硬实时、高可靠等需求，且工业环境呈现电磁干扰强烈、金属遮挡严重、人员移动频繁等特点。传统中继节点部署问题已是NP-完全问题，而工业应用的新需求和恶劣环境进一步增加了该问题的求解难度。已有部署算法不进行问题拆分而整体求解这使其在进行大规模IWSN部署时遭受算法性能显著衰减、时间复杂度大幅增长等问题。为此，本文提出了“问题拆解”、“子问题求解”和“优化合并”三阶段中继节点部署方案框架。该方案框架借助“分而治之”的思想降低整体问题求解复杂度并通过对局部解的优化合并保证算法性能。该部署方案框架在工业环境中充分考虑了部署成本、生命周期、实时性、可靠性等网络性能约束，形成了一套满足多约束、大规模工业无线网络部署方案。 基于该中继节点部署方案框架，本文具体解决了以下四类问题： （1）面向成本的中继节点部署问题：针对工业应用大规模、低成本要求，提出了基于邻居分组的连通敏感中继部署算法。该算法通过迭代依次从未被覆盖传感器节点中按邻居关系选取一组传感器节点，并将针对该组的几何圆盘覆盖问题抽象为集合覆盖问题求解，进一步将局部解合并问题建模为欧式距离优化问题，最终基于解析几何理论求解并采用最小生成树算法构建全局网络连通性。该算法有效克服了已有算法性能随网络规模衰减的缺陷，保证了算法在大规模部署时的性能。 （2）面向生命周期的中继节点部署问题：针对工业应用对IWSN长时间稳定、可靠运行要求，提出了基于聚类的容错部署算法。该算法根据能耗约束和地理邻近信息将传感器节点进行聚类分组，即将地理邻近且总能耗满足能耗约束的无线传感器节点划为一个分组，由于每个分组满足能耗约束从而将整体大规模、多约束问题有效降解为若干小规模斯坦纳树问题。最终，基于最小生成树为传感器节点构建至汇聚节点冗余通路，以此满足工业应用对可靠性、容错性要求。已有算法没有考虑工业对可靠性要求且无法保证算法近似比，而该算法在多项式时间下能够保证近似比，可有效保证算法性能。 （3）面向实时性的中继节点部署问题：针对工业应用对IWSN的实时传输要求，提出了基于集合覆盖的部署算法。该算法基于邻居关系将大规模、多约束连通性问题进行逐层分解，在分解过程中利用最短路径树剔除不满足实时性约束的部署位置，从而将每层子问题抽象建模为无需考虑实时性约束的小规模集合覆盖问题。在利用贪心算法求解局部集合覆盖问题后，基于剪枝技术合并局部解，从而进一步提高算法性能。该算法能够保证比已有算法更优的近似比。 （4）面向实时、可靠的中继部署问题：目前已有算法皆基于理想0-1信道模型，无法适用于恶劣的工业射频环境。为此，提出了基于实时信道质量测量的部署方法。该方法采用自汇聚节点端向传感器端逐跳迭代部署的策略，将每次迭代子问题抽象为集合覆盖问题并基于最短路径树算法删除不满足实时性约束的部署位置，在该子问题求解过程中每部署一个中继节点就通过实际信道质量测量调整中继节点部署位置，以此保证通信可靠性。该方法充分考虑了恶劣工业射频环境等因素对部署的影响，克服了已有算法基于理想0-1信道模型无法保证通信可靠性的问题。 综上，论文对IWSN中继节点部署问题进行了较为系统和深入的研究，旨在为IWSN中继节点部署提供一套较为实用的部署方案以及理论支撑

Delay constrained relay node placement in wireless sensor networks

无线传感器网络中考虑时延约束的中继节点部署(delay constrained relay node placement,DCRNP)问题通过部署最少数量的中继节点使得所有传感器节点与汇聚节点之间都有满足时延约束条件的通路.DCRNP问题已经被证明是NP-hard问题.本文提出基于汇合点及剪枝技术的中继节点部署(convergence-pruning-based relay node placement,CPRNP)算法近似求解DCRNP问题.CPRNP算法分为两个阶段,第1阶段找出所有可能使满足时延约束的通路相交的汇合点,并生成一棵以汇聚节点为根节点连接所有传感器节点的最短路径树;在第2阶段..

Delay constrained relay node placement in wireless sensor networks

无线传感器网络中考虑时延约束的中继节点部署(delay constrained relay node placement,DCRNP)问题通过部署最少数量的中继节点使得所有传感器节点与汇聚节点之间都有满足时延约束条件的通路.DCRNP问题已经被证明是NP-hard问题.本文提出基于汇合点及剪枝技术的中继节点部署(convergence-pruning-based relay node placement,CPRNP)算法近似求解DCRNP问题.CPRNP算法分为两个阶段,第1阶段找出所有可能使满足时延约束的通路相交的汇合点,并生成一棵以汇聚节点为根节点连接所有传感器节点的最短路径树;在第2阶段..

Mixed media access control method for chained wireless sensor network

本发明涉及无线网络技术，具体地说是一种面向链式无线传感器网络的混合介质访问控制方法。本发明方法充分考虑输电线路监测等应用的无线传感器网络链式或线型拓扑结构的特征，在网络不同时段采用了不同的接入策略，提出繁忙时期的时分访问控制Pipelined?TDMA以及空闲时期的竞争访问控制S-XMAC方法。在繁忙时期，采用了流水线式的调度传输方法来避免隐藏终端问题，以提高传输可靠性和资源利用率；在空闲时期，设置簇首和普通簇成员采用不同的MAC参数，在使簇首簇首和簇成员能够更及时地响应请求的同时，使得普通簇成员尽可能地节省能量，从而使得网络在节省能量的同时，满足应用系统对网络实时性的要求。</p

Delay constrained relay node placement in two-tiered wireless sensor networks: A set-covering-based algorithm

As Wireless Sensor Networks (WSNs) are widely used in time-critical applications, e.g., factory automation and smart grid, the importance of Delay Constrained Relay Node Placement (DCRNP) problem is becoming increasingly noticeable. Considering the benefits in terms of energy efficiency and scalability brought by the two-tiered topology, this paper studies the DCRNP problem in two-tiered WSNs. To address the NP-hardness, a Two-phase Set-Covering-based Algorithm (TSCA) is proposed to approximately solve this problem. To be specific, in the first phase, a Connectivity-aware Covering Algorithm (CCA) places Relay Nodes (RNs) to fully cover distributed sensor nodes with respect to delay constraints, and meanwhile CCA tries to reduce the number of connected components in the topology constructed in this phase so as to save the RNs deployed to build network connectivity. In the second phase, the network connectivity is built in obedience to delay constraints by a Set-Covering-based Algorithm (SCA) through an iterative manner, which formulates the deployment of RNs at each iteration as the set covering problem and solves this problem using a classic set covering algorithm. In addition, the elaborated analysis of time complexity and approximation ratio of the proposed algorithms is given out. Finally, extensive simulations demonstrate that TSCA can significantly save deployed RNs in comparison to existing algorithms

Relay Node Placement in Wireless Sensor Networks With Respect to Delay and Reliability Requirements

Wireless sensor networks are gradually employed in many applications that require reliable and real-time data transmission. As hop count is an important factor affecting end-to-end delay and reliability, we investigate the hop constrained relay node placement (HCRNP) problem in this paper. First, to achieve connectivity requirement, we study the connected HCRNP problem. Then, to design survivable network topologies against node failures, we study the 2-connected HCRNP problem. Correspondingly, two polynomial-time algorithms: cover-based 1-connected node placement (C1NP) and cover-based 2-connected node placement (C2NP) are proposed, respectively, to address the above two problems. Through rigorous analysis, we show that 1) C1NP has an approximation ratio better than existing algorithms for the connected HCRNP problem (i.e., O(1) for special settings and O($\ln n$) for arbitrary settings, where $n$ is the number of SNs) and 2) C2NP is the first algorithm that can provide an explicit performance guarantee for the 2-connected HCRNP problem, i.e., whenever C2NP finds a feasible solution, the ratio of this solution to the optimal solution is guaranteed to be O($\ln n$). Finally, we verify the effectiveness of the proposed algorithms through extensive simulations

A novel local search approximation algorithm for relay node placement in Wireless Sensor Networks

In two-tiered Wireless Sensor Networks (WSNs) relay node placement considering resource constraints and high overhead of the relay nodes plays a key role in extending the network lifetime. Therefore, approaches that support fewer relay nodes are desired to cover the WSNs. In this paper, we formulate the relay node placement problem as a Geometric Disc Covering (GDC) problem, and propose a novel local search approximation algorithm (LSAA) to solve the GDC problem. In the proposed LSAA, the sensor nodes are allocated into independent groups and then a Set Cover (SC) for each group is performed. The set of the SC for each group constitutes a SC of the GDC problem. LSAA is extensively investigated and analyzed by rigorous proof and the simulation results presented in this paper clearly demonstrate that the proposed LSAA outperform the approaches reported in literature in the reduction in deployed relay nodes

Relay node deployment method in time delay limited wireless sensor network

本发明涉及无线网络技术，具体地说是一种时延受限无线传感器网络中的中继节点部署方法。该方法包括覆盖与连通两个步骤，覆盖步骤的主要目的是在时延约束条件下用尽量少的中继节点覆盖所有传感器节点，而连通步骤的主要目的是在时延约束条件下用尽量少的中继节点构建网络连通性。其中覆盖包括可行部署位置分组、分组选择和可行位置选择三个步骤；连通包括可行性检验、连通性构建和中继修剪三个步骤。本发明充分考虑时延受限无线传感器网络对于时延和部署成本的要求，提出一种时延受限双层无线传感器网络中基于集合覆盖的中继节点部署方法，在满足网络时延要求的前提下通过部署尽量少的中继节点构建网络连通性