The proposed projects are subject to change. Please prioritize your interested directions during online application.
Project 1. Hydrogen production using solid oxide photoeletrochemical cells and visible lights
Water splitting using photoelectrochemical cells (PECs) has received increasing scientific interest in recent decades (17-29). The PEC is a single device that integrates a solar cell and an electrolysis cell. Based on a thorough literature review, the majority of investigations on semiconductor-based photocatalytic hydrogen generation have focused on materials development and novel cell configurations, in order to harvest more solar energy in the visible spectrum as well as increasing energy conversion efficiency. Most of the research is confined to aqueous electrolytes, which provides ionic charge transfer in low temperature PEC cells.
We will focus on proof-of-concept research on a revolutionary concept, solid oxide photoelectrochemical cells (SOPCs) for hydrogen production from steam at high temperature (400 - 800°C). The proposed all solid-state SOPC consists of an ion-conductive electrolyte, a hydrogen electrode, and a photocatalytic/oxygen electrode. The electrolyte is oxygen ion conductive at high temperatures and it has been widely used in solid oxide fuel cells. The hydrogen electrode is a metal-based porous electrode, such as platinum and nickel. The photocatalytic/oxygen electrode is able to absorb more visible sunlight at elevated temperature. The preliminary investigation includes characterization of the Schottky barriers of metal oxide semicondutors with noble metals at elevated temperatures. The objective is to find suitable semiconductors that can operate efficiently and harvest visible lights at high temperature.
Project 2. Reversible Solid Oxide Cells for Hydrogen Production and Electric Power Generation
The objective of this project is to evaluate the durability of reversible solid oxide cell (RSOC) in both the electrolysis and the fuel cell modes. Large-scale non-fossil hydrogen production is an important technology that impacts the hydrogen economy. However, most hydrogen production is based on fossil fuels including natural gas, oil, and coal. Non-fossil large-scale hydrogen production methods are gaining increasing interest all over the world. High temperature electrolysis (HTE) is one of the most efficient technologies for the production of carbon-free hydrogen at large scale (30). Besides the demand for large-scale hydrogen production, operation of reversible solid oxide cells (RSOC) gains growing interests (31). By integrating a RSOC system into a power plant, hydrogen can be produced through high temperature electrolysis at times of low power demand and stored as an energy source. During periods of high power demand, additional electricity can be generated from the stored hydrogen by RSOC operation in the fuel cell mode (32). However, although solid oxide fuel cells (SOFCs) can be directly operated in the electrolysis mode, practically they exhibit much higher degradation rates in the electrolysis mode than in fuel cell mode (33). Homemade RSOCs will be performed long term (200 hrs +) tests in the apparatus shown in Figure 5. The degradation will be recorded in both modes and scan electron microscope with X-ray microanalysis (SEM/EDS) will be used to characterize the degradation mechanism in the micro scale.
Project 3. Ultralight interconnects of PEM fuel cell stack used for unmanned aerial vehicle
Unmanned aerial vehicles (UAVs) are being used more and more frequently by the United States Military as a low cost, low risk option to manned flight. Fuel cells are of particular interest due to their longer flight endurance than battery and quieter operation than internal combustion engine (ICE). Most fuel cell stacks are designed for ground vehicle and stationary applications, in which weight is not the main concern. The UAVs however, requires a light weight power source that is at least comparable to ICE. The majority of fuel cell stack weight comes from its metallic interconnects (bipolar plates) and end plates (shown in Figure 7) (34). To reduce the weight of the stack, all the metallic components need to be replaced by lightweight materials.
Our current research focuses on fabricating composite thermoplastic bipolar plates for the lightweight fuel cell stack. Lightweight thermoplastic materials with high temperature and chemical stability, such as polylactic acid (PLA), Polyphenylsulfone (PPSF), and Polycarbonate (PC), will be used as the backbone of the interconnect. Silver or carbon particles will be used as the filling materials for electric conduction. REU students will be involved in fabricating the extrusion filament for 3D printing using the components mentioned above. Thereafter the bipolar plates will be fabricated using a 3D printer. Finally the properties, including mass density, electric conductivity, and thermochemical stability, will be evaluated.
Project 4. Application of electrochemical hydrogenation (ECH) in biofuels production
Hydrogenation and deoxygenation of biomass-derived oxygenated hydrocarbons (e.g. bio-oil, biocrude, lipids, and water-soluble organic compounds) are the two key reactions in the production of liquid hydrocarbons from biomass feedstock. These reactions convert oxygenated compounds and unsaturated bonds into chemically reduced forms with higher hydrogen content. Conventionally, heterogeneous catalysis in the presence of hydrogen is used for performing these goals. However, it usually requires high temperature (250 to 600ºC), pressure, regeneration or activation of catalyst. The novel electrocatalytic hydrogenation (ECH) methods bear some advantages over the conventional processes. Along with the milder reaction temperature (≤ 80ºC) and ambient pressure conditions, the enhanced products selectivity can be achieved by careful control of electrode potential. The process benefits from in situ generation of hydrogen since the use of aqueous reaction media reduces the need of hydrogen during hydrogenation reactions. The ECH can overcome low H2 solubility in aqueous (H2O) media by forming H2 on catalytic metal surface. The required electricity for ECH can be generated using renewable (photovoltaics, wind, natural gas and biomass) sources. This helps in addressing the future need for liquid biofuels and the need to storage of renewable electricity in liquid hydrocarbons.
The current team have been collaborating on ECH of algal lipids recovered after flash hydrolysis and the ECH of unsaturated fats (e.g. linolenic, linoleic, and oleic acids). The saturation of double bond functional groups reduces the reactivity, corrosiveness and also increases the H/C ratio closer to 2. One of the examples of electrocatalyst is the use of ruthenium supported on activated carbon cloth. A polymer electrolyte membrane fuel cell (PEMFC) is used to supply protons for ECH. The PEMFC consists of a typical membrane electrolyte assembly (MEA), gas diffusion layers, and end plates.
Project 5. Participation in NSF-CAREER Project
Presently, the co-PI Kumar is the PI on following project: Project Title: “CAREER: Nutrients and Energy-rich Macromolecules Recovery from Microalgae using Subcritical Water” Award Period: 01/01/2014 - 12/31/2018. Award Number: 1351413, Energy for Sustainability. The current NSF CAREER is a research cum educational project on biofuels and environmental sustainability. The objectives (Figure 8) of the research/educational goals are on integrating the research by educating the students and local communities about the benefits of chemical-free and environmentally benign processes for algae to biofuels and nutrients management. The additional goals are focused on training students in interdisciplinary subjects, environmental issues, and STEM area to develop energy and environment literate workforce. All the research efforts proposed in the current NSF award provide an excellent context to involve students from the Hampton Roads area through the proposed REU program. The involvement of REU students will help in communicating the need of an interdisciplinary approach in addressing the complex alternative energy and environmental engineering issues. The REU students will be involved in following two research studies: 1) Flash hydrolysis (FH) of algae proteins into aqueous phase; 2) Study the recycling of nutrients recovered after FH for algae cultivation to close the loop.
Project 6. Designer algae for photoautotrophic synthesis of advanced biofuels from CO2 and water
This research employs interdisciplinary methods in combination with synthetic biology and fundamental engineering research to achieve enhanced utilization of CO2 for photoautotrophic production of “drop-in-ready” carbon-based transportation fuels, such as butanol, directly from water and carbon dioxide (35). One of the key ideas here is to genetically introduce a set of designer genes encoding a set of specific enzymes to interface with the Calvin-cycle activity so that certain intermediate product such as 3-phosphoglycerate (3-PGA) of the Calvin cycle could be converted immediately to biofuels such as butanol. The net result of the envisioned total process including photosynthetic water splitting and proton-coupled electron transport for generation of NADPH and ATP that supports the Calvin cycle and the butanol production pathway is the conversion of CO2 and H2O to butanol (CH3CH2CH2CH2OH) and O2. Therefore, theoretically, this could be a new mechanism to synthesize biofuels (e.g., butanol) directly from CO2 and H2O. This photobiological biofuels-production process (Fig. 2) completely eliminates the problem of recalcitrant lignocellulosics by bypassing the bottleneck problem of the biomass technology. Since this approach could theoretically produce biofuels (such as butanol and/or related higher alcohols) directly from water and carbon dioxide with high solar-to-biofuel energy efficiency, it may provide the ultimate green/clean renewable energy technology for the world as a long-term goal.
Our work will integrate the high salt and alkalinity tolerance, the designer biosafety mechanism and the designer biofuel-producing function into a single algal strain for demonstrations of photoautotrophic synthesis of “drop-in-ready” advanced biofuels such as butanol directly from seawater and CO2 with ensured biosafety(36, 37). Recently, we have successfully generated the first set of transgenic thermophilic cyanobacteria (transformants) with certain designer butanol-production-pathway genes in our synthetic biology research effort. The Lee Group is also conducting experimental testing of cyanobacterial tolerance to various alcohol biofuels.
Project 7. Computational, photocatalytic, and mechanistic studies of clusters with a Co4O4 core: Influence of a possible stabilized Co(IV) intermediate and choice of terminal ligand and oxidant
With the evidence of an increase in the concentration of CO2 which has been implicated as one of the main cause of global warming on Earth, it is believed that such an increase is due to the burning of fossil fuels. As such, many scientists around the world have been developing catalysts for water oxidation and the generation of hydrogen from water with the use of “artificial photosynthesis” via the renewable energy of sunlight absorption. In reality, artificial water oxidation catalysis is poised to become a commercially significant technology in the near future. A detailed understanding of the structure and reactivity of certain candidates as catalysts are expected to play an essential role in further catalyst design and optimization.
Today, water oxidation catalysts (WOCs) with the Co4O4 cuboidal core have been used as substitutes for the costly noble metal catalysts. As a reference, photosynthesis is capable of water splitting much faster than any artificial catalyst that is made from first row transition metals. Recently Craig Hill and co-workers used the complex [Co4(H2O)2(PW9O34)2]10-, while Dismukes and co-workers have utilized [CoIII4O4(CH3CO2)4(py)4] (Figure 10) and [CoIII4O4(bpy)4(CH3CO2)2](ClO4)2 for water oxidation in the presence of the photosensitizer, [Ru(bpy)3]Cl2 and the oxidant, S2O82-, all in a homogeneous aqueous media.
This interdisciplinary project will make key contributions to the fundamental knowledge base of converting solar radiation to environmentally-friendly, carbon-free, combustible chemical fuels. The work targets the important problem of developing improved catalysts capable of splitting water. The REU students will assist in the synthesis and characterization of ligands and complexes, and will be involved in the use of spectroscopy in elucidation of structures of each compound and assist in carrying out electrolytic and photocatlytic studies. The REU student will learn how to acquire electrochemical, NMR, and EPR spectroscopic data as part of the project.
Project 8. Bio-methanol impurity impact on direct methanol fuel cell membrane and electrodes
Direct methanol fuel cell (DMFC) is considered as a promising alternative portable power source (38). Conventional the fuel used in DMFCs is methanol, which is made from fossil fuels, such as natural gas. Bio-methanol emerges as an alternative fuel for DMFCs as the global demand for renewable fuel is rapidly growing. Bio-methanol is made from biomass using the syngas process (39). However, various impurities can be introduced during the production process of bio-methanol. Those impurities could cause contamination of the proton exchange membrane assembly of DMFCs. Typically, impurities such as buthanol, methyl formate, and diisopropyl ehter exist in bio-methanol fuel (39). The impacts of those impurities on the catalyst and membrane are therefore subject to investigation prior to commercialization.
The objective is to find out the tolerance level of DMFC to each bio-methanol impurity. The test apparatus is set up as shown in Figure 11, in which a premixed impurity is introduced into the fuel stream. In this project, REU students will perform a series of electrochemical experiments to investigate the poisoning effects of bio-methanol. Cyclic voltammetry (CV) will be used to investigate adsorption of impurities on the catalysts as well as its capability of recovery. Electrochemical impedance spectroscopy (EIS) will be used to characterize the contamination of both the electrodes and the membrane during real time operation.
Project 9. Computational Fluid Dynamics of Microalgae Flash Hydrolysis to Produce Biofuels
This project will look into the study of flash hydrolysis of microalgae for protein extraction and production of biofuels intermediates. The advantage of using flash hydrolysis is that it transforms microalgae into biofuel intermediates without the use of added chemicals. The process involves only water and algae slurry mixed together at a high temperature to then react in order to extract proteins and create lipid-rich biofuel intermediates. This results in biofuel production that is energy-efficient and far less harmful to the environment then it would be if transesterification were used. This one of a kind project of fuel production from algae involves many scientific aspects; such as multiphase flows, turbulent flows, transport of particles in fluid flows, compressible flows, heat transfer, numerical modeling, and high performance parallel computing and scientific computation. The two most critical components of the process are a mixing chamber where algae slurry is mixed with high temperature subcritical water to heat it up, and a reactor where the actual Flash Hydrolysis occurs. We have successfully performed computational fluid dynamics simulations of part of such process and they are the first simulations ever of such process. The results so far are very exciting but the simulations need to be improved using more robust models. The nature and the scope of this project are very important to humanity as the FlashHydrolysis of algae is proposed to produce fuel; this is energy for the world. The objective of this project is to propose improvements to the process to make it more efficient and scalable. The students involved in the project will join Dr. Ayala’s research team. We meet in a regular basis every week to keep track of the projects. They will also be involved in: 1) developing research plans, 2) writing scientific papers, 3) collecting and analyzing data, and 4) presenting research results in group meetings and possible conferences.
Project 10. Grain and Grain Boundary Geometrical Shape Considerations on Alkali Diffusion Through Molybdenum and CIGS Films in Solar Cells
It has been found that higher efficiencies of Cu(In,Ga)Se2 (CIGS) solar cells can be achieved by incorporating small amount of sodium (Na) into the CIGS film to improve open-circuit voltage and fill factor. A common substrate used for CIGS solar cells is a Molybdenum (Mo) coated soda-lime glass (SLG). The SLG acts as a source of Na and the Mo thin film serves as transport gate for Na diffusion from the SLG into the CIGS. On the other hand, other researchers have found that a Potassium (K) treatment to CIGS layer has been also beneficial for its performance but interestingly found a depletion of Na concentration as a result of K concentration. They argued that the exchange occurred due to ion exchange reaction. It is therefore particularly important to study the diffusivity of alkalis such as Na and K in Mo and CIGS thin films and the diffusion mechanism that occur. To the best of our knowledge, very few studies have attempted to directly characterize the diffusion and provide diffusivity constants in Mo thin films and none of them have considered directly the grain size effect on the experimental SIMS intensity data, which might has biased the measured diffusion coefficient so far obtained. It is currently believe that most of the diffusion of most alkalis occurs through the grain boundaries and preliminary studies in our research group have led to conclude that the ratio of grain boundary size and grain size is not constant along Mo and CIGS film as opposed to how it has been treated up to now. It is therefore important to consider it when analyzing diffusion processes in thin films. The nature and the scope of this project are very important to humanity as the improvement of solar cells performance will lead to produce more energy for the world. The objective of this project is the gauge on the importance of the ratio of grain boundary size and grain size in thin film diffusion processes. We will use computer simulations for such studies. The students involved in the project will join Dr. Ayala’s research team. We meet in a regular basis every week to keep track of the projects. They will also be involved in: 1) developing research plans, 2) writing scientific papers, 3) collecting and analyzing data, and 4) presenting research results in group meetings and possible conferences.