Kinetic and Thermodynamic Aspects of Voltage as a Driving Force for Ammonia Activation

Renewable energy sources, such as solar and wind, have become increasingly prevalent and helped drive progress toward decarbonization of electricity. The commodity chemical industry is a large consumer of energy and a major contributor to global greenhouse gas emissions, and electrification of the industry using renewable sources is a possible step toward reducing the carbon footprint of chemicals. In this thesis, I first propose a paradigm where electrochemical systems enable bond-formation steps in the chemical industry, leveraging voltage as an alternative driving force to enable operation at mild temperatures and pressures. I then aim to answer the question “If I can apply mechanical energy (pressure), thermal energy (temperature), or electrical energy (voltage) to a chemical reaction, which should I use?” In particular, I present a universal expression for the equilibrium constant of a chemical reaction as a function of thermodynamic driving forces, and demonstrate how this universal equation and facile visualization of chemical reactions enables quick and informed justification for electrochemical versus thermochemical energy sources. I then focus on the particular case of electrochemical utilization of ammonia, a ubiquitous nitrogen precursor throughout the chemical industry. First, I look at an electrochemical analogue to reductive amination, where a carbonyl group is converted to an amine. Specifically, I demonstrate the electrochemical reductive amination reaction of benzaldehyde and ammonia and investigate its kinetics. I find that the reaction proceeds via an inner-sphere route at heterogeneous metal surfaces, in contrast to most previous work on outer-sphere electrochemical reductive amination systems. I then investigate the kinetics of activating ammonia by breaking the nitrogen-hydrogen bond oxidatively, and I find that the reaction proceeds through an outer-sphere, radical pathway. Last, I propose an energy storage paradigm that leverages ammonium formate, a combination of ammonia and formic acid, to store renewable electricity. I discuss the advantages of this fuel and demonstrate how voltage can aid in the release of energy from this fuel. Overall, in this thesis I start with the broad question of why and when to choose electrochemistry over traditional thermochemical routes in the chemical industry, and I then focus in on how electrochemistry can aid in the utilization of ammonia for both synthesis reactions as well as energy storage purposes.

Name thesis:degree_name

Doctoral

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Chemical Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2021

Author dc:creator

• Schiffer, Zachary J

Advisor dc:contributor.advisor

• Manthiram, Karthish

Statement dc:rights

• In Copyright - Educational Use Permitted
• Copyright MIT

Licence dc:rights.uri

• http://rightsstatements.org/page/InC-EDU/1.0/

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/140088

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/140088