Studying All Scales from the Atomic to the System Level

1. Reactor Design

Reactor design encompasses engineering the scale, transport, kinetics, and stability of electrolytic reactors. To this end, this area of our research seeks to understand material interactions within the materials (membranes, electrodes, and integrated components) used in electrochemical technologies, including CO₂ & CO Electrolysis and electrodialysis. Understanding the interrelationship between ionomers, catalysts, membranes, and gas diffusion media will optimize reactant and product transport, kinetics, and distribution. We also utilize spatial differences in the electrochemical reaction to develop novel reactor diagnostics to better understand these relationships. 

The Reactor Engineering team is focused on building electrochemical reactors at relevant scales for industrialization. Allison and Hunter focus on using electrochemical and reactor characterization techniques to understand reaction kinetics and transport as a function of reactor size. Recep used to lend expertise in CO₂ Reduction on gas diffusion electrodes to designing architectures and materials for electrochemical reactors, especially zero-gap designs. 

 

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2. Operando Electrochemical Characterization

Operando electrochemical characterization can provide incredibly valuable information about the electrochemical microenvironment where the reaction takes place. We utilize several probes to understand the electrode surface chemistry, including Electrochemical Atomic Force Microscopy (EC-AFM), Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS), operando cyclic voltammetry, in-situ Raman spectroscopy, rotating ring disk electrode voltammetry (RRDE), and other novel techniques currently in development. These techniques hope to develop an understanding of the electrochemical double layer, the active reactant species, and the nature of ionomer and water activity in the catalyst microenvironment. 

Understanding the chemical microenvironment of electrochemical systems is crucial to developing better reactor systems. The electrode-electrolyte interface is of particular interest to our group, as we have shown that electrochemical CO₂ reduction on gas diffusion electrodes must occur at the solid-liquid boundary. To better understand this system, we combine Fourier Transform Infrared Spectroscopy (FTIR) and EC-AFM to observe the evolution of the chemical microenvironment, especially as a function of the potential at the catalyst surface. Yuval works with the spectroscopic systems, using infrared probes to examine surface adsorbates, including both reactants and contaminants, such as ionomers incorporated into the double layer, and reaction conditions, such as local pH. Maria focuses on using EC-AFM  to examine the catalyst itself under CO₂RR reaction conditions, probing surface restructuring under polarization and other local conditions. Rachel uses RRDE to make real-time measurements of product selectivity on CO₂-to-CO electrocatalysts and investigate the effect of electrode coatings on selectivity.

 

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3. Computational Modeling

To understand electrochemical processes at the atomistic scale, we have leveraged computational tools such as the Joint Density Functional Theory software (JDFTx), which accounts for solvation and applied bias. Our focus is currently on developing continuum-scale models to understand microscopic transport processes that scale to macroscopic observables. These techniques are made possibly by our access to CU’s Alpine cluster and NREL’s Eagle and Kestrel clusters.

Computational modeling is becoming increasingly relevant in electrochemical research as we seek to scale-up devices and optimize processes that span multiple time- and length-scales. Our Computational Modeling team works to develop models that can be both predictive and descriptive of the highly correlated and complex processes that dominate electrochemical device performance, while also working closely with the Reactor Engineering team and the Operando Electrochemical Characterization team to form research questions and validate the models. Techniques that the team implements into their research include:

• Quantum Mechanical models, such as Joint Density Functional Theory (JDFT) which can rapidly expedite the discovery of new, more stable electrocatalysts. See our recent work on the use of JDFT to screen Metal-Nitrogen-Carbon catalysts, where a graphene sheet is doped with functional metals to promote catalysis.

• Continuum Modeling is relevant to understanding transport processes at the micro- to macro-scale that dictate the performance of electrochemical reactors at scale. This type of modeling ties in closely with the experimental observables gathered by the Reactor Design team. Reactions, diffusion, migration, and convection behaviors are all captured by the mesoscale technique. Some of our work can be found here, here, and here. 

• Microkinetic modeling is highly versatile and can give insight into the relative reaction rates and abundance of species participating in electrochemical reactions. It can be coupled to the aforementioned techniques through boundary conditions or by the development of hierarchical models. Microkinetic modeling ties in well with the observables gathered by the in-situ and operando spectroscopy team, and is utilized to various degrees in our work.

Hussain and Paige led the effort on catalyst discovery using JDFT. Hussain has moved to work with our Process Systems Engineering Team starting from the Fall of 2021. Paige continued to work on the presented computational modeling techniques and has expanded her expertise to include the application of the Generalized Modified Poisson-Nernst-Plank (GMPNP) model for NO3 reduction and transport through ion exchange membranes. Recep was our lead on performing continuum models to understand both local effects in the porous electrodes and bulk effects in the electrolyzers.

 

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4. Process Systems Engineering

To realize electrochemical systems that can be readily integrated to meet society's needs, we need to understand how they can be integrated with current and future energy systems as well as with carbon capture technologies. Techno-Economic Assessment (TEA) is a powerful tool to understand which operational conditions are realistic for CO₂ reduction systems. Life Cycle Analysis (LCA) is implemented to understand design criteria for the durability of reactor materials. These insights provide feedback loops with the Reactor Design team.

 

To guide the transition towards the decarbonization of the life cycle of chemicals through the industrial implementation of CO₂ reduction, we combine our experimental results and reaction models with process systems engineering tools for the systematic assessment and optimization of CO₂ reduction systems: 

• Mathematical models (e.g., MATLAB-based, python-based) and commercial simulators (e.g., Aspen Plus) are used to build robust models of the process. Optionally, we integrate these models into other tools through surrogate models. 

• Techno-Economic Assessment (TEA) is a powerful tool to evaluate the costs and revenues of industrial-scale facilities for CO₂ reduction. 

• Life Cycle Analysis (LCA) is implemented to quantitatively assess the environmental impact of CO₂ reduction systems and evaluate the potential of the technology to mitigate carbon dioxide emissions and decarbonize the synthesis of chemicals. 

• Mathematical optimization can be applied to enhance the technology at different levels, from process control to the supply chain. We focus on the process integration of renewably-powered electrolysis with CO₂ capture from air.

These insights provide feedback to the Reactor Design team in the form of operational targets. Hussain is closely working with our previous postdoctoral fellow, Dr. Ana Somoza-Tornos, focusing on the integration of Direct Air CO₂ Capture (DACC) technologies with electrochemical carbon utilization methods. In addition, Nithila is working directly with Hussain on carbon accounting of DACC technologies through life-cycle assessment. In the past, Allison worked closely with the process integration team at NREL, leveraging her experience in TEAs for renewable transit during her time at RMI. Hussain is co-advised by Dr. Bri-Mathias Hodge, who was also co-advising Ana when she was at CU.

 

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