(7dk) Rational Materials Design for Energy and Heterogeneous Catalysis Applications: Noble Metal Single Atom Catalysts and 1D Nano-Array Support Materials

Many industrial catalysis, environmental remediation, and energy conversion processes rely heavily on expensive noble metal nanoparticles (NPs) dispersed on high-area porous supports. For examples, Pt-based supported catalysts have been extensively utilized for vehicle emission control (45% of global demand) and chemical production and petroleum refining (9% of global demand). Noble metals are also effective co-catalysts for boosting the efficiency of photocatalysis, in which the semiconductor supports act as both light absorbers and catalysts. Rational material design for both metal catalysts and supports has been proved effective to improve catalysts’ efficiency, selectivity, and stability while reducing material usage. Reducing catalyst NP size, ultimately to isolated single atom dispersion, can increase the number of active sites, thus reducing material usage. Additionally, catalytic behavior of metals can be affected by size reduction via several channels: (1) increased unsaturated coordination, (2) quantum confinement effect, (3) metal−support interactions, and (4) cluster configurations. Therefore, single atom catalysts (SACs) often possess unique properties that cannot be achieved by the nanoscale counterpart. However, due to their high surface free energy, SACs are often unstable, hindering their practical applications. Anchoring and localizing single metal atoms onto support surfaces are essential to designing and developing efficient and stable supported metal SACs. One-dimension nano-array structured support materials such as nanowire-, nanorod- and nanotube-arrays have demonstrated as an emerging class of catalysts and supports. The combination of 1D confinement effects and collective properties of long-range ordered structure often leads to interesting electrical, optical, and thermal transport properties. Interfacial reactions are also facilitated on 1D nano-array catalysts. Recent advances in synthesis and fabrication methods allow engineering of 1D nano-array materials with well-defined exposed crystal facets and defects, thus enabling tunable metal-support interaction, which in turn can be exploited to stabilize supported single atom catalysts.

As faculty, I plan to apply my expertise in rational nanomaterials design and characterization to establish material design principles for efficient and stable noble metal SACs supported on 1D nano-array materials. My initial focus will be directed on catalytic and photocatalytic properties of the materials for environmental remediation and solar energy conversion applications. The materials can be investigated for heterogeneous catalysis application such as propane dehydrogenation and CO₂ reduction.

Proposal Experience. Proposals submitted to NSF (PFI: AIR-TT) and DOE (BES and VTO).

Research Experience.

My research career path has been a blend of heterogeneous catalysis, nanomaterials and nanotechnology, (photo)electrochemistry, and high-vacuum instrument design. In my dissertation work, I set about to tackle one of the most challenging problems in the field of photocatalysis, which is finding efficient photocatalyst materials that satisfy stringent conditions for photoelectrochemical water splitting. Our highly collaborating work on this topic resulted in several publications in peer-reviewed journals such as Nano Letters, Journal of American Chemical Society, ACS Nano, some of which are among the top 1% highly cited by Web of Science. For examples, my works on synthesis and characterization of visible light active TiO₂ nanowire arrays have set a benchmark for the performance of N-doped TiO₂ materials and helped to elucidate the role of incorporated N to the visible light activity, which has been a subject of debate for decades. Furthermore, I discovered a new method to reduce the band gap of TiO₂ using the interaction of N and Ti³⁺. In one of my postdoc research work, we applied excitonic energy transfer schemes to enhance light harvesting in ultrathin crystalline Si solar cells. We developed a hybrid solar cell platform, which utilizes a proximity quantum dot layer as energy transfer donor to sensitize the Si active layer. This study offers an approach for the rational design and integration of energy transfer and optical coupling structures for the improvement of light harvesting in optoelectronic devices. Currently, I am leading an effort in the development a scalable method to integrate single atom Pt catalysts/TiO₂ nano-arrays for diesel oxidation catalysts, which involves the collaboration between four universities, three DOE national labs, and one industry manufacturer.

Teaching Interests:

In addition to my passion for doing research, the desire to teach/mentor is one of the primary reasons I want to pursue a career in academia. I really enjoyed the experience as a teaching assistant for several chemical engineering laboratory courses. I also have extensive experience in mentoring undergrad, grad, and postdoc researchers from diverse backgrounds. I take pleasure in encouraging students’ critical thinking, facilitating a team-working environment, and improving students’ organizing and goal-orientating skills, as well as creating lesson plans so that students can apply their knowledge to solve practical problems.

Due to my diverse education and research background, I am confident teaching courses in different topics, including most general subjects within the chemical engineering curriculum for both undergraduate and graduate students. I would be most effective in teaching kinetics and reactor design, electrochemical engineering, materials science, transport phenomena, and fundamental laboratory classes.

Selected Publications.

1. Hoang, S; Gao, P., “Nanowire Array Structures for Photocatalytic Energy Conversion and Utilization: A Review of Design Concepts, Assembly and Integration, and Function Enabling,” Advanced Energy Materials, http://dx.doi.org/10.1002/aenm.201600683

2. Hoang, S.; Ashraf, A.; Eisaman, M. D.; Nykypanchuk, D.; Nam, C.-Y., "Light Harvesting and Energy Transfer in Ultrathin Inorganic Solar Cells," Nanoscale 2016. http://dx.doi.org/10.1039/C5NR07932B

3. Hoang, S.; Guo, S. W.; Hahn, N. T.; Bard, A. J.; Mullins, C. B., "Visible Light Driven Photoelectrochemical Water Oxidation on Nitrogen-Modified TiO2 Nanowires," Nano Letters, 2012, 12 (1), 26-32. http://dx.doi.org/10.1021/nl2028188

4. Hoang, S.; Berglund, S. P.; Hahn, N. T.; Bard, A. J.; Mullins, C. B., "Enhancing Visible Light Photo-oxidation of Water with TiO₂ Nanowire Arrays via Cotreatment with H₂ and NH₃: Synergistic Effects between Ti³⁺ and N", Journal of the American Chemical Society, 2012, 134 (8), 3659-3662. http://dx.doi.org/10.1021/ja211369s