Nelson Y. Dzade

Dr. Dzade leads the Materials and Minerals Theory Group (MMTG) in the Department of Energy and Mineral Engineering at Penn State. The MMTG sits on the interface of Physical Chemistry, Applied Physics, Applied Mathematics, Computer Science, Machine Learning, Materials & Minerals Science and Engineering, and specializes in the development of first-principles electronic structure and atomistic simulation methods in synergy with novel experimental approaches to: (a) Accelerate the rational design and development of advanced functional materials for renewable energy conversion and storage applications (e.g. solar cells, batteries, and supercapacitors); (b) Describe surface and interface phenomena in heterogeneous catalyssis and provide mechanistic insights into the thermodynamics and kinetics of catalytic reactions; (c) Unravel interfaces in semiconductor structures and devices, as well as predict the band alignment and offsets at semiconductor/insulator interfaces, as they control transport phenomena at these interfaces and characteristics of devices employing these interfaces; (d) Provide atomic-level insights into environmentally relevant reactions and geochemical processes occurring at mineral surfaces/interfaces, including crystal growth, adsorption reactions, mineral extraction and dissolution, and redox reactions at mineral surfaces.

Research within MMTG is carried out in close collaboration with leading experimental groups in the field and from worldwide academic institutions. Below are the four main strands of our research activities.

1. Rational design of earth-abundant next-generation materials for energy conversion and storage

The energy trilemma - energy security, energy accessibility, and environmental sustainability is emerging as a critical challenge for the development of government energy policies. Meeting the ever-increasing global energy demands, while at the same time drastically reducing carbon emissions from the overreliance on and usage of fossil fuels remains one of the most critical challenges for humankind in the 21^st century. Solar power has a tremendous capacity to provide society with clean energy by displacing coal and oil used for electricity generation and transport. The solar resource is super-abundant and freely available. Harnessing this energy and designing our infrastructure around it will mitigate the environmental and societal impacts of climate change. Today, solar technologies already contribute to varying degrees to national energy productions. However, for solar energy to be rapidly established as part of the mainstream electricity industry at a reduced cost, devices must be made from inexpensive and earth-abundant materials. Under this research theme, we employ cutting-edge materials theory and simulation to predict novel solar absorber materials composed of earth-abundant elements; and engineer existing materials to improve their stabilities and solar conversion performances. Recurring themes here include bandgap engineering, interface engineering, band alignment and offset engineering. The magnitude of band offsets controls transport phenomena across interfaces and characteristics of PV devices, hence their accurate determination and engineering are vital to improving the performances of PV devices. We are very interested in Battery energy storage systems (BESS), which play an increasingly pivotal role between green energy supplies and responding to electricity demands. BESS are devices that enable energy from renewables, like solar and wind, to be stored and then released when customers need power most. Under the BESS theme, we employ first-principles density functional theory (DFT) methods to accelerate the exploration of high-performance energy materials and predict structure-property-performance relations in electrode materials.

2. Computer-aided rational design of active and robust heterogeneous catalysts

New catalysts are needed to improve the efficiency of industrial processes and drive energy conversion and environmental mitigation processes. Achieving the required catalytic performance (activity and selectivity) gains depends on exploiting the many degrees of freedom of materials development including multiple chemical components, nanoscale architectures, and tailored electronic structures. Using predictive modeling is the only intelligent and efficient path forward to sift through the many degrees of freedom. Under this research theme, we employ first-principles electronic structure calculations in collaboration with an experiment to provide reliable insights into the thermodynamics and kinetics/dynamics of the elementary steps involved in model catalytic reactions such as CO₂ conversion, hydrogen evolution reactions (HER), dye degradation, etc. The synergistic computational-experiments approach provides the most profound and detailed insights into how chemical reactions proceed and how we can control their finest details.

3. Chemical functionalization of nanoparticles and surfaces

Nanoparticles have major impacts in fundamental research and many industrial applications due to their unique size- and shape-dependent properties such as electrical, magnetic, mechanical, optical, and chemical properties, which largely differ from those of the bulk materials. Because nanoparticles have different surface structures and thus different surface interactions compared to larger particles, they have an extremely high tendency toward adhesion and aggregation. It is therefore important to develop synthesis techniques to control the dispersion or aggregation of nanoparticles that dictate their crystal shape. Control of nanocrystal shape is important in various applications, such as in heterogeneous catalysis, solar cells, light-emitting diodes, and biological labelling. Generally, the synthesis of nanoparticles involves surfactant molecules that bind to their surface and stabilize the nuclei, thus preventing larger nanoparticles against aggregation by a repulsive force between the adsorbates. Chemical functionalization thus controls the growth of nanoparticles in terms of the rate, final size or geometric shape. However, due to the complex nature of the interface between organic functional groups and nanoparticle facets, the interface chemistry is difficult to determine by purely experimental means. Under this research theme, we employ accurate first-principles calculations to predict the lowest-energy adsorption structures of organic molecules at inorganic surfaces and unravel how the adsorption influence the stabilities of the different nanoparticle facets. Based on calculated surface energies, the final shape/morphology of the nanoparticle can be predicted using Wulff Construction.

4. Surface Geochemistry and Computational Mineralogy

Practically all environmentally relevant reactions in nature that involve minerals are surface or interface reactions. Be it crystal growth, adsorption reactions, mineral extraction and dissolution, redox reactions, or even the growth of crystallites from the melt, the actual reactions take always place at mineral surfaces. To understand and influence these processes it is desirable to obtain a detailed insight into the surface and interface interactions at the molecular level. Molecular simulations provide mechanistic insights into the adsorption process and accurately predict the structures and properties of the adsorption complexes of contaminants onto iron oxide-hydroxide and sulfide surfaces, which is critical for the quantification of the adsorption. When it comes to the recovery of critical and rare earth minerals from various sources, froth flotation is a commonly used technique. This involves the adsorption of both organic and inorganic reagents at the mineral-water interface, with the objective of selectively rendering the target mineral(s) hydrophobic to recover it in the froth phase. Collectors, which contain a polar group and a non-polar aliphatic chain, can be adapted in terms of chain length, unsaturation, and ramification, as well as functionalized polar groups. Moreover, all these reagents can be combined to improve the flotation performances (selectivity or target minerals recovery). All these optimizations are difficult to investigate by purely experimental methods and molecular modeling is a powerful tool to gain a detailed atomic-level understanding of the adsorption mechanisms of flotation reagents at the mineral-water surfaces. We aim to develop robust theoretical models and employ atomistic simulations (DFT and MD simulations) to describe the mineral-water interface and the adsorption mechanisms of collector molecules at finite temperatures and pressures in the froth flotation process. The derived atomic-level insights are expected to motivate rational design and selection of future collector molecules for enhanced recovery of critical minerals.