Novel 3-D printing of catalytic nanodiodes

圣母大学的首席研究员 Eduardo Wolf 在 NSF 先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测该设备复杂性所需的工具。该概念基于这样的假设：电子转移效应将以与肖特基结中类似的方式发生在催化剂金属-载体界面处。沃尔夫希望通过纳米制造一种模拟这种效应的装置来控制催化剂的活性和选择性，这将允许通过外部偏置电压进行催化控制，就像在二极管整流结中控制电子流一样。直到最近，由于缺乏适当的纳米加工工具，阻碍了纳米级的实现。PI Wolf 在之前的 CBET 奖项中取得了进展。这一概念得到了第一原理模拟的支持。 Wolf 开发了多层增强红外反射吸收光谱技术，利用偏振红外并改变偏振和入射角来检测吸附在 Pt 纳米线上的 CO 分子的方向。接下来，使用 MEIRAS 技术演示了 Pt/TiO2 催化二极管上 CO 吸附过程中的电子转移。最后，证明了通过外部偏置电压控制反应速率（CO 吸附）。该结果证明了化学键的控制可以通过外部电压实现的假设，这是催化领域之前未研究过的变量。尚待完成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二维表面积有限以及每个器件的纳米制造成本，其中涉及必须在不同设备中单独执行的多个步骤。因此，当前的纳米加工技术与工业催化剂的制备肯定不具有竞争力。Pt/TiO2/Au多层结构的制备是使用光学光刻来创建底部和顶部电极，然后是电子束蒸发，然后是电子束光刻。结果，沉积在 TiO2 顶部的 5 nm Pt 薄膜虽然具有电连续性，但在原子水平上具有粗糙的表面，存在裂纹和一小部分暴露的 Pt/TiO2 界面。PI Wolf 将获得 ENG 催化和生物催化计划颁发的 EAGER 奖，以开展高风险实验，评估一种改进的催化二极管制造方法，涉及桌面纳米加工和大规模多路复用束笔光刻技术，以在3D打印机，但覆盖3？磁盘而不是先前设计中制造的 4x4 mm 区域。据 Wolf 所知，3D 打印以前从未在催化剂设计中尝试过。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，这可能会对催化、传感器和太阳能领域产生重要影响，就像 3D 打印对制造、医学和生物学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.