化学势依赖于系统内的所有物质

在热力学中，关于多元系的化学势的变量集，有互不一致的两种结论.一种结论认为，某种物质的化学势，仅仅依赖于其它物质的存在，另外一种认为，不仅依赖于其它物质，也依赖于自己.本文通过详细的分析论证了，一般而言，化学势依赖于系统内的所有物质.     

射频等离子制备石墨烯负载Co3O4催化剂及其析氧性能研究

氢能的引入能有效提升配电网的供电可靠性,而电解水制氢是实现低碳转型的关键技术,开发高效的电解水催化剂势在必行。过渡金属氧化物储量大、催化活性高,是具有广阔应用前景的析氧反应催化剂。本文通过射频等离子体处理制备石墨烯上负载Co₃O₄析氧催化剂,XRD、Raman和XPS测试结果显示,二维结构石墨烯的引入加速表面电子迁移,增大了反应面积。等离子体处理促进了纳米粒子在石墨烯上的负载,利用等离子体刻蚀作用在催化剂表面制造出大量碳结构缺陷和氧空位结构,改善了活性位点分布,有效调控Co₃O₄电子结构,提高析氧催化活性。电化学测试表明,本文中合成的Co₃O₄@rGO在电流密度为50 mA·cm^-2时的过电位为410 mV,动力学反应速率较快,表现出优于商业IrO₂的析氧催化活性。     

广义加权损失函数下准备金的分位信度估计

由于聚合数据是个体数据的加总,会失去一些有用信息.针对个体数据模型,分位回归模型可以直接求取未决赔款准备金的分位数,并且对数据中存在的异常值的敏感度不高.在程纪(2020)模型基础上,将分位回归模型与信度理论相结合,将多个流量三角形的增量赔款数据看成是相同日历年下的重复性多次观测,体现样本数据的分层结构,克服经典信度模型中只有一条回归线的弊端,在广义加权损失函数下得到准备金的信度估计,并给出参数估计.     

Mg,N掺杂β-Ga2O3光电性质的第一性原理计算

通过基于密度泛函理论的第一性原理计算,研究了Mg单掺杂、N单掺杂和不同浓度的Mg-N共掺杂β-Ga₂O₃的结构性质、电子性质和光学性质,以期获得性能比较优异的p型β-Ga₂O₃材料。建立了五种模型:Mg单掺杂、N单掺杂、1个Mg-N共掺杂、2个Mg-N共掺杂和3个Mg-N共掺杂β-Ga₂O₃。经过计算,3个Mg-N共掺杂β-Ga₂O₃体系的结构最稳定。此外,在5种模型中,3个Mg-N共掺杂β-Ga₂O₃体系的禁带宽度是最小的,并且N 2p和Mg 3s贡献的占据态抑制了氧空位的形成,从而增加了空穴浓度。因此,3个Mg-N共掺杂β-Ga₂O₃体系表现出优异的p型性质。3个Mg-N共掺杂体系的吸收峰出现明显红移,在太阳盲区的光吸收系数较大,这归因于导带Ga 4s、Ga 4p、Mg 3s向价带O 2p、N 2p的带间电子跃迁。本工作将为p型β-Ga₂O₃日盲光电材料的研究和应用提供理论指导。     

水热法制备二氧化锡/钨酸铋复合光催化材料及其催化活性研究

本文用水热法制备了正交晶系的纳米球状结构的二氧化锡和正交晶系的由片状聚集成球状结构的钨酸铋,并且对二者进行了复合,制备出了二氧化锡/钨酸铋复合光催化材料。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、比表面积测试仪(BET)、紫外可见分光光度计等技术对复合样品的结构、形貌、比表面积、孔容孔径和光学性质进行了表征。用碘钨灯模拟太阳光,分别以二氧化锡、钨酸铋和二氧化锡/钨酸铋复合材料为催化剂降解罗丹明B(RhB),研究所制备的二氧化锡/钨酸铋复合材料的光催化活性。光催化90 min时二氧化锡、钨酸铋和二氧化锡/钨酸铋对罗丹明B的降解率分别是9%、22%和30%。实验结果表明,在可见光下,二氧化锡/钨酸铋复合材料的光催化活性要高于单一的二氧化锡和钨酸铋。     

基于抛光基材的热蒸镀铜箔生长高平整单层石墨烯薄膜

在石墨烯的化学气相沉积工艺中,铜箔是决定石墨烯薄膜质量的重要因素。传统铜箔由于制备工艺的限制,存在大量的缺陷,导致石墨烯薄膜的成核密度较高。本工作选用抛光铝板、抛光不锈钢板、微晶玻璃和SiO₂/Si作为基材,用热蒸镀法制备了不同粗糙度的铜箔,并详细讨论了以该系列铜箔生长高平整度石墨烯薄膜的条件及铜箔对石墨烯薄膜品质的影响。实验结果表明,铜箔以(111)取向为主,与基材分离后,表面具有纳米级平整度。在生长石墨烯后,从SiO₂/Si剥离的铜箔成核密度是4种基材中最小的。同时,从SiO₂/Si剥离的铜箔晶体结构变化最不明显,具有良好的结晶性,表面几乎不存在铜晶界缺陷。当压强为3 000 Pa,氢气和甲烷流速分别为300 mL/min和0.5 mL/min时,可以获得约1 mm横向尺寸的石墨烯单晶晶畴。     

g-C3N4-W18O49复合光催化剂的制备及其光催化机理研究

通过简单的溶剂热法成功制备出了g-C3N4-W18O49复合光催化剂,采用XRD、SEM、TEM以及PL对所得催化剂的物相结构及形貌和光学性能进行了表征,通过降解甲基橙和光解水产氢实验研究所得催化剂的催化性能及其催化机理.由实验可知,W18O49的含量为50;时所得g-C3N4-W18O49复合光催化剂的降解性能最好,其降解率比纯g-C3N4纳米片提高48;;为进一步研究复合光催化剂的电子-空穴传输机理,我们又进行了光解水制氢实验.结果表明:单一的W18O49无产氢活性,它的复合明显降低了g-C3N4的产氢速率,说明复合结构中光生电子是从g-C3N4传递到了W18O49,表现出明显的Ⅱ型异质结复合特征,而不是部分文献所提出的Z型方式.     

基于NiCo2O4纳米片电极的非对称混合电容器

The looming global energy crisis and ever-increasing energy demands have catalyzed the development of renewable energy storage systems. In this regard, supercapacitors (SCs) have attracted widespread attention because of their advantageous attributes such as high power density, excellent cycle stability, and environmental friendliness. However, SCs exhibit low energy density and it is important to optimize electrode materials to improve the overall performance of these devices. Among the various electrode materials available, spinel nickel cobaltate (NiCo₂O₄) is particularly interesting because of its excellent theoretical capacitance. Based on the understanding that the performances of the electrode materials strongly depend on their morphologies and structures, in this study, we successfully synthesized NiCo₂O₄ nanosheets on Ni foam via a simple hydrothermal route followed by calcination. The structures and morphologies of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis, and the results showed that they were uniformly distributed on the Ni foam support. The surface chemical states of the elements in the samples were identified by X-ray photoelectron spectroscopy. The as-synthesized NiCo₂O₄ products were then tested as cathode materials for supercapacitors in a traditional three-electrode system. The electrochemical performances of the NiCo₂O₄ electrode materials were studied and the area capacitance was found to be 1.26 C·cm^-2 at a current density of 1 mA·cm^-2. Furthermore, outstanding cycling stability with 97.6% retention of the initial discharge capacitance after 10000 cycles and excellent rate performance (67.5% capacitance retention with the current density from 1 to 14 mA·cm^-2) were achieved. It was found that the Ni foam supporting the NiCo₂O₄ nanosheets increased the conductivity of the electrode materials. However, it is worth noting that the contribution of nickel foam to the areal capacitance of the electrode materials was almost zero during the charge and discharge processes. To further investigate the practical application of the as-synthesized NiCo₂O₄ nanosheets-based electrode, a device was assembled with the as-prepared samples as the positive electrode and active carbon (AC) as the negative electrode. The assembled supercapacitor showed energy densities of 0.14 and 0.09 Wh·cm^-3 at 1.56 and 4.5 W·cm^-3, respectively. Furthermore, it was able to maintain 95% of its initial specific capacitance after 10000 cycles. The excellent electrochemical performance of the NiCo₂O₄ nanosheets could be ascribed to their unique spatial structure composed of interconnected ultrathin nanosheets, which facilitated electron transportation and ion penetration, suggesting their potential applications as electrode materials for high performance supercapacitors. The present synthetic route can be extended to other ternary transition metal oxides/sulfides for future energy storage devices and systems.