Our research focuses on the development of reactive and catalytic nanomaterials for applications in water treatment, nutrient recovery, and energy conversion. We aim to design catalytic materials and conduct experimental research on the synthesis, characterization, and performance testing of catalysts and catalyst-support composite materials. We primarily focus on non-precious metal and metal oxide/hydroxide catalyst materials, and we aim to identify catalyst compositions and morphologies that are particularly useful for specific reactions. To do this, we have developed catalyst synthesis methods where synthesis parameters can be logically and systematically varied to understand the resulting catalyst properties and how properties affect catalyst performance. Our ultimate goal in this research approach is to understand synthesis-property-performance relationships and from this understanding, design and create catalysts optimized for a particular application. Our research encompasses a mixture of fundamental and applied engineering research, from the study of fundamental material properties and performance mechanisms, to scale-up, technology integration, and commercialization
Nanoparticle Synthesis & Composite Fabrication
Our synthesis methods primarily focus on aqueous-based chemical reduction and oxidation reactions that induce particle precipitation. Our approach is scalable; we are able to synthesize concentrations from 10 mg/L to 10-20 g/L in a batch.We synthesize both alloy and core-shell nanoparticle morphologies, and nanoparticle size is controlled through the presence of specific water-soluble organic ligands. These ligands enable the precipitation of metal and metal oxide particles at the nanoscale; without the presence of ligands, particles would grow beyond the nanoscale. In designing catalyst materials, we think about multi-metallic combinations within the nanoparticle morphology, and we consider immobilization of the nanoparticles onto specific support materials. The nanoparticle composition and morphology are two important parameters that affect catalytic performance, and these two parameters can be optimized based on the reaction.Support materials, such as high surface area carbon, can also be a critical component of catalyst design; support materials can impart added functionality and allow increased reactivity through a variety of mechanisms including adsorption, catalyst stability, electron donation, and catalyst dispersion/location.
Water Contaminant Adsorption and Degradation
The increasing use and reuse of our limited water resources necessarily means that water contaminants will continue to be identified and will continue to accumulate in our water sources. While technologies exist to address water contaminants, we will continue to need improvements and advancements in treatment technology to better address a wide variety of water contaminants, from organic chemicals, pharmaceuticals, and personal care products, to heavy metals, pesticides/herbicides, and other toxic compounds. One opportunity that we see is to develop catalyst materials that can cost-effectively address a range of water contaminants and that can be integrated into current water treatment processes as a reactive degradation step. Iron-based nanoparticles have been extensively investigated at the laboratory bench-scale as a potential materials for reactive water treatment applications, and contaminant studies have thoroughly demonstrated that iron nanoparticles can remove contaminants through a combination of adsorption and reactive degradation. Yet iron nanoparticles remain limited to bench-scale demonstrations and some short-term in situ groundwater treatment studies. Iron nanoparticles are limited in their application due to three primary challenges: uncontrolled reactivity (and resulting short lifetime), oxidation and precipitation as iron oxides (with a loss in reactivity), and uncontrolled agglomeration and transport/immobilization in specific systems. Thus, there are critical and important engineering challenges that must be solved to enable iron-based reactive nanoparticles to eventually be used as a wide-spread water treatment technology. Further, opportunities exist to creatively design iron-based nanoparticles for specific contaminant and technology implementation scenarios.
Electrochemical Ammonia Generation
Globally, the discovery and commercialization of the Haber-Bosch process for the production of ammonia from nitrogen and hydrogen over 100 years ago revolutionized how crops are fertilized. As a result, food production, and the global population, increased exponentially, and we currently depend on the Haber-Bosch process for food production and availability today. However, the Haber-Bosch process, which operates at high temperature and pressure, is energetically inefficient, and the source of hydrogen primarily comes from methane gas steam reforming. Steam reforming of methane, or coal, results in the production of carbon dioxide, and thus, Haber-Bosch ammonia production is one of the top producers of greenhouse gases world-wide. Today, we look towards other potential processes and technologies as potentially more efficient and environmentally friendly alternatives to Haber-Bosch. One of the potential alternatives is the electrochemical reduction of nitrogen gas to ammonia through electrolysis of water, where the hydrogen atoms in a water molecule become the source of hydrogen for ammonia molecule formation. An electrochemical process for the reduction of nitrogen to ammonia would operate similar to an electrolyzer, where catalysts are used on the cathode and anode to reduce nitrogen and also enable oxygen evolution, respectively. This technology is scalable and potentially integratable with renewable energy sources (e.g., wind or solar), which would make the technology independent of fossil fuels. However, the electrochemical reduction of nitrogen to ammonia is extremely difficult due to a competing reaction, water reduction to hydrogen, that occurs within the same potential range as nitrogen reduction. Thus far, there has been little progress in the development of successful catalyst materials. Our research currently focuses on several unique approaches to the innovative design of non-precious metal catalysts to address the issue of reaction selectivity. Our research activities span from fundamental measurements of gas and water vapor adsorption to scale up and device-level testing of synthesized catalysts.
Water Electrolysis: H2/O2 Generation
With the commercialization and market penetration of fuel-cell-powered vehicles, the hydrogen economy is poised to grow and expand throughout the US and the world. Yet the production of hydrogen remains largely based on the conversion of fossils such as methane and coal. An alternative to the use of fossil fuels is the reduction of water molecules to hydrogen. Water splitting, or water electrolysis, is performed in a technology called an electrolyzer, where the anode and cathode are separated by a solid polymer electrolyte membrane. At the anode, oxygen molecules are evolved, while at the cathode, hydrogen molecules are evolved, and the membrane separator allows selective transport of either protons or hydroxyl anions. This type of device is similar to a fuel cell but operates in reverse; in a fuel cell, energy is produced when hydrogen (or another fuel) is oxidized (and water is produced) and electrons are captured, while in an electrolyzer energy is input to react water molecules and produce hydrogen and oxygen. In electrolyzers, the kinetics and overall efficiency is currently limited by the anode, where oxygen is evolved. Thus, better catalysts are needed to enable faster oxygen evolution; further, it is desirable for future devices to be designed to be free of precious metals in the catalyst. Thus, our research focuses on alkaline electrochemical systems, where catalysts comprised entirely of non-precious metals are stable and where the kinetics of oxygen evolution are potentially enhanced at high pH. Our catalyst research focuses on the synthesis and characterization of bimetallic and trimetallic nanoparticle catalysts for alkaline oxygen evolution, where we aim to create nanostructured catalysts with high mass activity and minimal mass transport limitations.