Figure showing the system size on the x-axis and the simulated period on the y-axis. This data points are represented by images of the different scales targeted by our group and their respective simulated period.

Decades of research on electrochemical CO2 reduction has brought the science to the cusp of the commercialization, with specialty chemicals already in industrial production. Our group'sÌýresearch uses the principles of electrocatalysis, electrochemical engineering, materials science, and computational power to develop electrolyzers that will make an order of magnitude leap in cell area, power, and efficiency.Ìý

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A 3D image of an electrochemical reactor assemblyA 3D image of an electrochemical reactor

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 & COÌýElectrolysis 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.Ìý

The Reactor Engineering teamÌýis focused on building electrochemical reactors at relevant scales for industrialization.ÌýAllisonÌýandÌýHunterÌýfocus on using electrochemical and reactor characterization techniques to understand reaction kinetics and transport as a function of reactor size.ÌýRecepÌýused to lendÌýexpertise in CO2ÌýReduction on gas diffusion electrodes to designing architectures and materials for electrochemical reactors, especially zero-gap designs.Ìý

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A figure showing an electrochemical cell in spectroscopy experiments2. Operando Electrochemical Characterization

Operando electrochemical characterization can provide incredibly valuable information aboutÌýthe 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,Ìýrotating ring disk electrode voltammetry (RRDE),Ìýand 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.Ìý

Understanding the chemical microenvironment of electrochemical systems is crucial to developing better reactor systems. TheÌýelectrode-electrolyte interface is of particular interest to our group, as we have shown that electrochemical CO2Ìýreduction on gas diffusion electrodes must occur at theÌýsolid-liquid boundary. To better understand this system, we combine Fourier Transform Infrared Spectroscopy (FTIR) and EC-AFMÌýto observe the evolution of the chemical microenvironment, especially as a function of the potential at the catalyst surface.ÌýA figure showing results from spectroscopy as well as an electrochemical cellYuvalÌýworks 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.ÌýMaria focusesÌýon using EC-AFMÌý 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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Computational results showing the applied potential effects on the energetics of MN4C electrocatalysts3. Computational Modeling

A 3D image of the molecular structure of MnN4CTo 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 thatÌýscale 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 A figure showing the length scales considered by our computational modeling team.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 rapidlyÌýexpedite the discovery of new, more stable electrocatalysts. See ourÌý 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 , , and .Ìý

  • 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 theÌýFall of 2021. Paige continued to work on the presented computational modeling techniques and hasÌýexpanded 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

Figure showing the process analysis techniques considered in the labTo 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)ÌýisÌýa powerful tool to understand which operational conditions are realistic for CO2 reduction systems. Life Cycle Analysis (LCA)Ìýis implemented to understand design criteria for the durability of reactor materials. These insights provide feedback loops with the Reactor Design team.

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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:Ìý

  • Mathematical models (e.g., MATLAB-based, python-based)Ìýand 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.Ìý

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

  • Another figure showing the process analysis techniques considered in the labLife Cycle Analysis (LCA)Ìýis 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.Ìý

  • 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 CO2ÌýCapture (DACC)Ìýtechnologies 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,ÌýAllison workedÌýclosely with the process integration team at NREL, leveraging her experience in TEAs for renewable transit during her time at RMI.ÌýHussain isÌýco-advised by Dr. Bri-Mathias Hodge, who was also co-advisingÌýAnaÌýwhen she was at CU.

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Future Work

We are also interested in studyingÌýprocesses beyond CO2Ìýelectrolysis,Ìýincluding:

  • CO2Ìýcapture from air using Direct Air CO2ÌýCapture (DACC) technologies
  • Integrated CO2Ìýcapture and conversion
  • Electrochemical conversion of methaneÌý
  • Anodic reactions beyond Oxygen Evolution Reaction (OER) that couple with CO2Ìýreduction