Novel 3-D printing of catalytic nanodiodes

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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.