Nanostructured Materials for Energy

I. Supercapacitors from metal sulfides with tunable pore structure

Complex metal sulfides have emerged as the new material system for electrodes in energy applications due to their high electrochemical activity combined with their low cost and portfolio of earth-abundant, non-toxic alternatives to standard materials. Compared to metal oxides currently in use, complex metal sulfides demonstrate better conductivity, greater mechanical and thermal stability, and higher performance. The lack of industrial-scale, cost-effective production methods, however, impedes widespread integration of metal sulfide nanostructures in electrodes. Furthermore, current production methods are unable to calibrate the electrodes pore structure (porosity), which is an important parameter for optimizing the performance of supercapacitors. In this project we are researching methods for scalable manufacturing of complex metal sulfide nanocrystals and assembling the nanocrystals into optimum porous electrode structures. The project uses electrophoretic deposition (EPD) to deposit nanocrystals with controlled porosity. Because the building blocks will be uniform in size (monodisperse), and because no additional additives (carbon black or binders) are used, the packing and pore structure can be quantified and tailored.


II. Tuning metal oxide electronic conductivity for energy materials

Oxides are well known as materials with low electronic conductivity. But upon closer examination, there is a great deal of variability in their ability to conduct charge, and much of this remains unexplained. In this project, a fundamental question is being investigated: how does atomic disorder affect conductivity? To characterize the oxides and determine the cation site information x-ray emission spectroscopy (XES), high-angle annular dark-field imaging, and electron energy loss spectroscopy to determine site occupancy, oxidation states, and local atomic segregation. The experimental results are coupled with theory to understand the mechanisms and outline a global model for transport. Semiconductor transistors, batteries, and fuel cells will benefit by elucidating the mechanisms to tailor conductivity in oxides.

Selected Publications:

“Breakdown of the Small-Polaron Hopping Model in Higher-Order Spinels,” A. Bhargava, R. Eppstein, J. Sun, M.A. Smeaton, H. Paik, L.F. Kourkoutis, D.G. Schlom, M. Caspary Toroker, and R.D. Robinson, Advanced Materials 32, 2004490 (2020), DOI:  10.1002/adma.202004490

“Mn Cations Control Electronic Transport in Spinel CoxMn3-xO4 Nanoparticles,” A. Bhargava, C.Y. Chen, K. Dhaka, Y. Yao, A. Nelson, K.D. Finkelstein, C.J. Pollock, M.C. Toroker, and R.D. Robinson, Chem. Mater. 31, 4228 (2019), DOI: 10.1021/acs.chemmater.9b01198


III. Nanoparticle surface treatment, activation, and attachment

One of the major hindrances in the application of colloidal nanocrystals is the presence of large organic surfactant ligands, which create highly insulating barriers and block electronic communication between nanocrystals. This project uses a variety of methods to activate the nanocrystal surface and assemble the nanocrystals into functional electrodes. For instance, this project uses (NH4)2S to completely remove bulky surfactant ligands and bind the nanocrystals together. This surface modification process is unique in that 1) no inorganic surfactant ligands – (NH4)2S or (NH4)S– are detected on the NCs after ligand removal, and the original surfactant ligands are efficiently eliminated in only a few seconds; 2) after ligand removal the NCs are connected through metal-sulfide bonding, but still retain quantum confinement.

Selected Publications:

“Assessment of Soft Ligand Removal Strategies: Alkylation as a Promising Alternative to High-Temperature Treatments for Colloidal Nanoparticle Surfaces,” A. Nelson, Y. Zong, K.E. Fritz, J. Suntivich, R.D. Robinson, ACS Materials Letters 1, 177 (2019), DOI: 10.1021/acsmaterialslett.9b00089

“Chalcogenidometallate Clusters as Surface Ligands for PbSe Nanocrystal Field-Effect Transistors,” C.R. Ocier, K. Whitham, T. Hanrath, and R.D. Robinson, J. Phys. Chem. C 118, 3377-3385 (2014), DOI: 10.1021/jp406369a

“Surfactant Ligand Removal and Rational Fabrication of Inorganically Connected Quantum Dots,” H. Zhang, B. Hu, L. Sun, R. Hovden, F.W. Wise, D.A. Muller, and R.D. Robinson, Nano Letters 11, 5356-5361 (2011), DOI: 10.1021/nl202892p

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