Novel 3-D printing of catalytic nanodiodes

诺特丹大学的首席研究员Eduardo Wolf在美国国家科学基金会的支持下研究了催化纳米二极管的概念，并投入了时间和精力来开发探测该装置复杂性所需的工具。这个概念基于一个假设，即电子转移效应将以类似肖特基结的方式发生在催化剂金属-支撑界面上。沃尔夫希望通过纳米制造一种装置来控制催化剂的活性和选择性，这种装置将模仿这种效应，并允许通过外部偏置电压来控制催化，就像在二极管整流结中控制电子流一样。直到最近，缺乏适当的纳米制造工具阻碍了在纳米尺度上的实现。PI Wolf在之前的CBET奖项中取得了进展。这个概念得到了第一性原理模拟的支持。Wolf提出了一种多层增强红外反射吸收光谱技术，利用偏振红外，改变偏振和入射角来检测吸附在Pt纳米线上的CO分子的取向。接下来，使用MEIRAS技术证明了CO在Pt/TiO2催化二极管上吸附过程中的电子转移。最后，证明了外偏置电压对反应速率（CO吸附）的控制。这个结果证明了一个假设，即化学键的控制可以通过一个外部电压来实现，这是一个在催化领域以前没有研究过的变量。但要做的是控制复杂反应的选择性。我们需要更多的纳米二极管来研究这种催化的新变量。目前设计的催化二极管的主要限制是其二维表面积有限，以及每个器件的纳米制造成本，这涉及多个步骤，必须在不同的设备中单独进行。因此，目前的纳米制造技术与工业催化剂的制备肯定没有竞争力。采用光刻法制备Pt/TiO2/Au多层结构，先制备底电极和顶电极，然后进行电子束蒸发，再进行电子束光刻。结果，沉积在TiO2顶部的5nm Pt薄膜虽然是电连续的，但在原子水平上表面粗糙，有裂纹和一小部分暴露的Pt/TiO2界面。PI Wolf将获得ENG催化和生物催化项目的EAGER奖，进行高风险实验，评估一种制造催化二极管的改进方法，该方法涉及大规模多路光束笔式光刻的桌面纳米制造，以在3d打印机中制造一个简单的催化二极管，但覆盖3？磁盘而不是在以前的设计制造的4x4毫米面积。至于狼的优点呢？据我所知，3d打印在催化剂设计方面还没有尝试过。因此，不能保证所提出的催化剂制备方法将产生具有催化二极管特性的催化剂。尽管如此，所获得的知识将为未来通过3d打印实现这项工作奠定基础，这可能会在催化、传感器和太阳能领域产生重要影响，就像3d打印在制造业、医学和生物学领域产生变革性影响一样。

Principal Investigator Eduardo Wolf of the University of Notre Dame has investigated the concept of the catalytic nanodiode with previous support from NSF and invested time and effort into developing the tools required to probe the intricacies of this device. The concept rests on the assumption that electron transfer effects will occur at catalyst metal-support interfaces in a similar way to those in a Schottky junction. Wolf hoped to control catalyst activity and selectivity by nanofabricating a device that will mimic this effect, and that will permit catalytic control by an external bias voltage in a similar way that electron flow is controlled in diodic rectifying junctions. Up until recently, the lack of proper nanofabrication tools prevented the realization at the nanoscale.PI Wolf made progress within the prior CBET award. The concept was buoyed with first principle simulations. The technique of Multilayer Enhanced Infrared Reflection Absorption Spectroscopy was developed by Wolf using polarized IR and varying the polarization and incidence angle to detect the orientation of CO molecules adsorbed on Pt nanowires. Next, electron transfer during CO adsorption on a Pt/TiO2 catalytic diode was demonstrated using the MEIRAS technique. Finally, the control of a reaction rate (CO adsorption) with an external bias voltage was demonstrated.This result demonstrates the hypothesis that control of the chemical bond can be achieved via an external voltage, a variable not studied before in the field of catalysis. Yet to be done is to control the selectivity of complex reactions. What is needed is more nanodiodes to study this new variable in catalysis. The main limitation of the catalytic diode as currently designed is that its 2D surface area is limited and the cost of nanofabrication of each device, which involves multiple steps that must be carried out separately in different equipment. Thus the current nanofabrication technique is certainly not competitive with the preparation of industrial catalysts.The Pt/TiO2/Au multilayer structure was prepared using optical lithography to create the bottom and top electrodes, and electron beam evaporation, followed by e-beam lithography . As a result the 5 nm Pt film deposited on the top of TiO2, although electrically continuous, had a rough surface at the atomic level, with cracks and a fraction of exposed Pt/TiO2 interfaces.PI Wolf will receive an EAGER award from the ENG Catalysis & Biocatalysis Program to carry out the high risk experimentation evaluating an improved methodology of fabricating catalytic diodes involving desktop nanofabrication with massively multiplexed beam pen lithography to fabricate a simple catalytic diode in a 3-D printer, but covering a 3? disk instead of the 4x4 mm area fabricated in the previous design. As to the best of Wolf?s knowledge, 3-D printing has not been attempted before in catalyst design. Thus, there is no guarantee that the proposed method of catalyst preparation will produce a catalyst with the characteristics of a catalytic diode. Nonetheless the knowledge acquired will create the foundation for future implementation of this work via 3-D printing which may have an important impact in the field of catalysis, sensors, and solar energy in the same way that 3-D printing is having transformative impact in manufacturing and medicine and biology.