Group Research

Mark Martirez – Assistant Project Scientist

Can we use light to speed up N2 dissociation for NH3 synthesis?

Ammonia (NH3) is one of the most essential agricultural compounds being used as the primary source of nitrogen in fertilizers. The Haber-Bosch process is a time-tested synthetic method for NH3 in large quantities from N2 and H2. While the reaction of N2 and H2 gas is thermodynamically allowed at room temperature and pressure, the initial dissociation of both reactants required to facilitate their combination is highly unfavorable, both thermodynamically and kinetically. Although a transition metal catalyst, such as Fe, may lower the barrier for the dissociation of N2, high temperature is still required to hasten this process, which consequently demands high pressure to remain nearly spontaneous. Through first-principles methods, I investigate alternative metal catalysts that could not only lower dissociation barrier for N2 but also harness the energy of light, via plasmon resonance, to facilitate this process. With light instead of heat as an additional driving force, a high-dissociation rate at lower temperatures may be achieved, which would then relax the need for higher pressures and thus improve the energy efficiency of the process overall.

Jan-Niklas Boyn – Postdoctoral Fellow

What are the fundamental, molecular processes underlying saline water-based CO2 capture?

The capture of CO2 from the earth’s atmosphere is a key strategy for the mitigation of global warming. However, conventional negative emissions technologies, such as the injection of CO2 into geological formations, require separate steps for the removal of CO2 from the air and its storage, resulting in significant energetic and logistical hurdles. The sequestration of CO2 from sea water, which contains CO2 at 150 times its concentration in air, provides a promising alternative to such methods. Here, one particularly promising proposal is the sCS2 approach where CO2 is mineralized into carbonate using an electrolytic reactor, enabling a one-step carbon capture and storage process that may be powered by renewable energy.  Yet, knowledge of the fundamental, molecular processes involved in such an approach is limited. We aim to perform multi-level simulations, harnessing both ab-initio correlated electronic structure theory, as well as molecular dynamics calculations to elucidate the mineralization pathways of carbonates with Mg2+ and Ca2+ cations in order to assess their viability in CO2 sequestration. Insights from these studies will provide valuable understanding for the design of large-scale mineralization facilities.

Ziyang Wei – Postdoctoral Fellow

How do we improve the efficiency of electrochemical carbon dioxide reduction reaction?

Copper remains the most important metal catalyst for electrochemical carbon dioxide reduction reaction into C2 products. Due to limited evidence from in situ experiments, mechanistic studies are often performed in the framework of density functional theory, using functionals at the generalized gradient approximation level, which have fundamental difficulties to describe correctly CO adsorption and surface stability. Using advanced first-principles quantum mechanics techniques, such as embedded correlated wavefunction (ECW) theory, we want to understand the complicated reaction mechanisms. We also work on the combination of the ECW theory with the implicit solvation and further the grand canonical treatment of electrons to model the solvation and electrochemical potential effects in the reaction process.

Xuelan Wen – Postdoctoral Fellow

What is the mechanism of plasmon-enhanced photocatalysis on antenna-reactor complexes?

Traditional plasmonic metals (Au/Ag/Cu/Al) have limited surface chemistry, while conventional catalytic metals (Pd/Pt/Ru/Rh) are poor optical absorbers. In antenna-reactor complexes, a catalytic reactor is placed adjacent to a plasmonic antenna. This combination dramatically increases photocatalytic efficiency, and sometimes selectivity too. Using various first-principles quantum mechanics techniques, such as density functional theory (DFT) and embedded correlated wavefunction (ECW) theory, we want to understand the reaction mechanisms involving ground state and multiple excited states. These insights further help us design better photocatalysts.

Robert Wexler – Postdoctoral Fellow

How can we improve the performance of solar cells?

Every hour, the sun delivers more energy to the Earth than we consume in a year. As such, the potential impact of solar energy is unmistakable as it far-exceeds global energy needs while simultaneously combating global warming due to its sustainability and carbon-neutrality. To capitalize on this opportunity, the scientific community has spent several decades searching for materials that efficiently absorb sunlight. A number of solar technologies have been commercialized, most notably those based on Si and Ru dyes. These and other promising materials, however, are unable to completely supplant fossil fuels because they are too expensive and/or toxic. Consequently, sunlight absorption, cost, and toxicity all must be considered concurrently to design an efficient, scalable, and environmentally friendly solar infrastructure. Recently, there has been growing interest in the solar material Cu2ZnSnS4 (CZTS), which contains inexpensive and nontoxic elements and possesses ideal sunlight absorption characteristics (namely, a band gap of ~1.4-1.6 eV). Unfortunately, under processing conditions, atoms can exchange sites (e.g., Zn and Sn), which leads to band gap reduction and the formation of localized electronic states in the band gap that can trap charge carriers. A fundamental theoretical understanding of these so-called antisite defects is still lacking, thus hindering the design of improved CZTS-based materials. In my research, I apply density functional theory calculations and thermodynamics both to enrich understanding of defect stability and structure and to identify promising doping schemes to limit the formation of defects detrimental to solar cell performance.

Benjamin Bobell – Undergraduate Student

How effectively can we simulate the mineralization of CO2 in sea water?

Through a mineralization process of carbon dioxide (CO2) into carbonates, such as CaCO3 and MgCO3, atmospheric CO2 can be removed from the atmosphere and stored. This mineralization process consists of reactions where either there is hydration of CO2 into carbonic acid (H2CO3) or local excess OH- aids the formation of bicarbonate (HCO3 – ) and carbonate (CO3 – ). I use a multi-level simulation process of both static and dynamic models, in which I build up the scale of my simulation to understand the molecular dynamics of CO2 and its mineralization process in seawater at the atomic level. Doing so will allow us to design materials that can accelerate a natural mineralization process that otherwise occurs at long geologic time scales. To describe the distribution of the electrons within the molecules, I use density functional theory (DFT) and correlated wavefunction (CW) methods. I use deep neural networks to learn and develop atomic potentials from DFT simulations for aqueous CO2 (and will eventually include Ca2+ , Mg2+), to understand CO2 mineralization in seawater.