摘要：高效非贵金属催化剂对于推进析氢反应(HER)的大规模工业化至关重要.碳化钼(Mo_(2)C)因其类似铂的能带密度和优良的中间产物吸附特性,有望替代贵金属基材料成为具有前景的催化剂.然而,它在常规制备过程中存在严重的晶体过度生长和团聚问题,导致催化效率低.本研究利用三聚氰胺辅助法制备了含有丰富表面和界面的超细碳化钼/氮化钼(Mo_(2)C/Mo_(2)N)异质结构,并同时将其嵌入到氮掺杂碳纳米纤维(CNFs)中.Mo_(2)C/Mo_(2)N异质结构的协同作用与超细纳米晶表面暴露的丰富活性位点共同提高了电催化活性,而氮掺杂碳纳米纤维框架保证了快速的电荷转移和良好的结构稳定性.此外,原位形成的Mo_(2)C/Mo_(2)N晶体与碳基质之间存在较强的界面耦合作用,进一步提高了电子电导率和电催化活性.得益于这些优势,Mo_(2)C/Mo_(2)N@N-CNFs在碱性溶液中表现出优异的电催化析氢性能,在电流密度10 mV cm^(-2)时具有75 mV的低过电势,优于单相Mo_(2)C@N-CNFs对比样以及近期报道的Mo_(2)C/Mo_(2)N基催化剂.这个合成方法集成了异质结构、纳米化和碳修饰策略,为设计高效率电催化材料提供了新的参考.

摘要：电子皮肤是先进医疗设备和智能机器人智能感知的核心器件.在电子皮肤中引入微结构可以提高灵敏度,同时也导致信号的非线性较窄的压力响应范围,这极大地限制了电子皮肤的应用.本工作中,作者设计了一种电容式电子皮肤,这种传感器采用了一种微柱电极和一种离子凝胶,二者接触后形成的离子-电子界面的面积随着压力的上升而增大.实验发现这种传感器同时具有高灵敏度、高线性度以及较宽的压力响应范围.这种极高的线性度源于微结构受压后发生结构硬化以及凝胶-电极之间力学匹配带来的补偿效应.作者将这种传感器应用于脉搏检测、足底压力分析和假肢抓取的压力分布测试等,证明了其在智能机器人和健康监测中有巨大的应用潜力.该工作通过简单的结构设计和材料刚度的匹配实现了柔性压力传感器的线性响应,为传感器的线性响应设计提供了新的思路.

摘要：The DC-DC converters are widely used in photovoltaic generating systems as an interface between PV module and the load. These converters must be chosen to be able to match the maximum power point (MPP) of PV module when climatic conditions change with different resistive load values. So DC-DC converters must be used with MPPT controller in order to reduce losses in the global PV system. This article focuses on the effect of climatic conditions on design of two components (inductance, capacitance) for three topologies of DC-DC converters commonly used in PV systems. When climatic conditions change, the boundary of inductance and capacitance parameters of DC-DC converter will change. These two parameters must be properly sized to achieve optimal efficiency for each converter. The design optimization is based on two principles: 1) for a steady-state operation in a continuous conduction mode, the inductance value for all choppers must be greater than the maximum value of boundary inductance, and 2) in order to limit the output voltage ripple of DC-DC converter below a desired value, the filter capacitance must be larger than the maximum value of boundary capacitance.

摘要：GaN (gallium nitride) buck-rectifier has been proposed to realize high power density ISOP (input series and output parallel)-IPOS (input parallel and output series) converter-based dc distribution system. The ultra-low loss bi-directional switch can be developed by the GaN power device because of the low on-resistance, the high-speed switching behavior and its own device structure. The buck-rectifier using the GaN bi-directional switches has the potential to achieve higher power density than the commonly utilized boost-rectifier. Availability of the GaN-HEMT (high electron mobility transistor) for the buck rectifier has been verified taking the theoretical limit of the on-resistance and the switching loss energy into account. Design consideration for a high power density buck-rectifier has been also conducted and the application effect of the GaN bidirectional switches has been evaluated quantitatively. The ISOP-IPOS converter-based dc (direct current) distribution system takes full advantage of the buck-rectifier and the rectifier using GaN devices contributes to realizing higher power density dc distribution system.