System-level approaches for intensifying the CO2 electrolysis process: from reaction chemistry to process development

Bhargava, Saket Sanjay

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https://hdl.handle.net/2142/115516 Copy

Description

Title

System-level approaches for intensifying the CO2 electrolysis process: from reaction chemistry to process development

Author(s)

Bhargava, Saket Sanjay

Issue Date

2022-03-16

Director of Research (if dissertation) or Advisor (if thesis)

Kenis, Paul J. A.

Doctoral Committee Chair(s)

Kenis, Paul J. A.

Committee Member(s)

• Gewirth, Andrew A.
• Yang, Hong
• Flaherty, David W.

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Carbon dioxide, Electroreduction, Electrochemical engineering, Process intensification, System-level, Process Development, Systems engineering, Electrocatalysis, Electrochemistry

Abstract

Carbon capture and utilization (CCU) is a promising approach to curb the rising CO2 levels in the atmosphere. The utilization of captured CO2 is particularly interesting because several carbon-based fuels, chemicals, and intermediates could be produced using CO2 as a feedstock. The electroreduction of CO2 (CO2RR) is an emerging platform to convert CO2 into carbon-based value-added chemicals (such as carbon monoxide (CO), formic acid (HCOOH), ethylene (C2H4), methanol (CH3OH), ethanol (C2H5OH), methane (CH4), acetic acid (CH3COOH), and n-propanol (C3H7OH)) using renewably powered electricity in a carbon-neutral manner. This dissertation employs a systems thinking-based multiscale approach to elucidate molecular-level mechanistic insights and develop system-level engineering approaches to intensify the CO2 electrolysis process and sustainably scale the process for industrial implementation. Chapter 2 of this dissertation highlights the several system and process considerations that need to be considered/worked on and how these considerations affect the key electrochemical performance metrics – current density (jtotal or jpartial), Faradaic efficiency (FEproduct), full-cell energy efficiency (EEproduct), conversion per pass (CPPproduct), and performance stability over time. The insights from these discussions will guide the de-risking of technology maturation of the CO2 electrolysis process and sustainable implementation at industrial scales. Chapter 3 of this dissertation focuses on developing system design rules for intensified electrochemical performance of CO2RR to CO. In particular, mechanistic insights into the role of electrolyte composition – cations and anions, identity of the rate determining step (RDS), and the influence of electrolyte cations on the RDS were used to tailor and optimize the electrolyte composition. Systematic process optimization of several key process parameters – cathode catalyst loading, electrolyte flow rate, electrolyte concentration, and CO2 flow rate – resulted in a state-of-the-art performance for electrochemical CO production under ambient conditions – a jCO of 866 mA/cm2 was obtained with a FECO of 98% at a cell potential of -3.0 V corresponding to an EECO of 43% and a CPPCO of 36% when using 3 M CsOH as the electrolyte flowing at 5 mL/min. Combined insights from mechanistic studies and systematic process optimization led to the formulation of system design rules (as semi-quantitative/qualitative function-property relationships) for high-rate, selective, and energy-efficient electrochemical CO production on silver nanoparticles. Chapter 4 of this dissertation focuses on reducing the energy consumption of a CO2 electrolyzer using earth-abundant metals-based catalysts and magnetic fields. In particular, the enhanced performance by switching from IrO2 to NiFeDAT at the anode and by using a magnetic field at the anode are explored using polarization curves, Tafel slopes, and magnetometry. The enhancement of mass transfer is also explained via the magnetohydrodynamic (MHD) effect. Energy savings of up to 64% were realized at jCO exceeding 300 mA/cm2. Chapter 5 of this dissertation explores the use of multivalent cations-based electrolytes for CO2RR. In particular, mechanistic insights into the role of multivalent cations revealed that these cations precipitate in the form of oxides and hydrides and block the active catalyst sites thereby hindering CO2RR. Electrochemical impedance spectroscopy was used in conjunction with Pourbaix diagrams to understand the origin of the formation of surface deposits. Grazing incidence X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize the surface deposits. Overall, this dissertation highlights some system-level approaches for intensifying the CO2 electrolysis process based on mechanistic insights and engineering approaches. A framework for the development of scalable and sustainable electrochemical systems based on electrochemical process systems engineering is also presented.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Saket Sanjay Bhargava

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