Novel 3-D printing of catalytic nanodiodes

圣母大学的首席研究员爱德华多·沃尔夫在NSF之前的支持下，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索该设备复杂性所需的工具。这一概念建立在这样的假设之上，即电子转移效应将发生在催化剂金属-载体界面上，其方式与肖特基结中的电子转移效应相似。沃尔夫希望通过纳米软化一种模仿这种效应的设备来控制催化剂的活性和选择性，并允许通过外部偏置电压进行催化控制，就像控制二极管整流结中的电子流一样。直到最近，缺乏合适的纳米制造工具阻碍了纳米级的实现。PI Wolf在之前的CBET奖中取得了进展。这一概念得到了第一性原理模拟的支持。多层增强红外反射吸收光谱技术是由Wolf发展起来的，它利用偏振红外，改变偏振和入射角来检测吸附在铂纳米线上的CO分子的取向。其次，用Meiras技术研究了CO在铂/二氧化钛催化二极管上吸附过程中的电子转移。这个结果证明了化学键的控制可以通过外加电压来实现，这是以前在催化领域中没有研究过的变量。然而，要做的是控制复杂反应的选择性。需要更多的纳米二极管来研究催化中的这一新变量。目前设计的催化二极管的主要限制是其2D表面积有限，以及每个器件的纳米制造成本，这涉及到必须在不同设备中单独执行的多个步骤。因此，目前的纳米加工技术与工业催化剂的制备相比肯定是不具竞争力的。采用光学光刻产生底部和顶部电极，然后电子束蒸发，然后电子束光刻的方法制备了铂/二氧化钛/金多层结构。结果，沉积在二氧化钛表面的5 nm铂薄膜，虽然是电连续的，但在原子水平上有一个粗糙的表面，有裂缝和一小部分暴露的铂/二氧化钛界面。PI Wolf将获得ENG催化与生物催化计划的热切奖励，以进行高风险实验，评估一种改进的方法，该方法涉及台式纳米制造，使用大规模多路复用束笔光刻来制造简单的催化二极管，但覆盖3？盘，而不是先前设计中制造的4x4 mm面积。据沃尔夫？S所知，在催化剂设计中，3D打印还没有尝试过。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打印实施这项工作奠定基础，3D打印可能会在催化、传感器和太阳能领域产生重要影响，就像3D打印对制造业、医学和生物学产生革命性影响一样。

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.