PhD defense: Jiefeng LIU – 28/11/2024

Jiefeng LIU

defended his PhD thesis on 28 Novembre 2024

Catalyst and electrolyte engineering for applications in paired CO₂ electrolysis
and CO₂ reactive capture

Front of the jury:

– Jennifer PERON, Professeure, Université Paris Cité – Rapporteur
– Juqin ZENG, Assistant professor, Politecnico di Torino – Rapporteur
– Gabriel LOGET, Chargé de Recherche au CNRS, University of Rennes 1 – Examinateur
– Philippe MIELE, Professeur, Université de Montpellier – Directeur de thèse
– Damien VOIRY, Directeur de Recherche au CNRS, Université de Montpellier – Co-Directeur de thèse

Abstract:

The rapid development of the global economy has driven a sharp increase in energy demand, exacerbating environmental issues such as pollution, resource depletion, and global warming. As fossil fuel reserves dwindle and the effects of climate change intensify, the need for sustainable energy solutions becomes increasingly urgent. The Paris Climate Agreement has accelerated global efforts to reduce carbon emissions and transition to cleaner energy sources. In this context, electrocatalytic carbon dioxide reduction (CO₂RR) emerges as a promising technology, capable of converting CO₂ into valuable chemicals and fuels, thus contributing to a closed carbon cycle and supporting industrial sustainability.

However, CO₂RR faces significant challenges, including the need for more efficient, selective, and scalable catalytic systems, and the high energy costs associated with traditional processes like the oxygen evolution reaction (OER). So far, most of the studies of CO₂RR have been investigated in refining catalysts, optimizing electrolytes, and designing more efficient electrolyzers. Therefore, I aimed to address these challenges by exploring advancements in catalyst and electrolyte engineering to gain further insights into paired CO₂ electrolysis and CO₂ reactive capture, with the goal of improving the CO₂RR for practical applications.

In this thesis, I firstly reviewed the state of CO₂ reduction technologies, with emphasis on electrocatalysis as a key method for achieving carbon neutrality. Then I presented the optimization of gas diffusion electrodes (GDEs) through spray deposition techniques. Copper-based catalysts, particularly CuPd alloys, demonstrated enhanced ethylene selectivity, while carbon black and Nafion ionomer coatings improved stability and performance in large electrodes. Large-area electrodes with 25 cm² also show potential for practical CO₂ reduction applications. I then introduced a novel approach by pairing CO₂RR with ethylene glycol oxidation (EGOR) instead of the traditional oxygen evolution reaction (OER). Using nickel-iron layered double hydroxide (NiFe-LDH) as the EGOR catalyst, this method reduced energy consumption by 38% for CO and 31% for C₂₊ products, showing potential for scalable CO₂ electrochemical conversion. Furthermore, I explored the direct utilization of flue gas for CO₂RR, addressing challenges posed by oxygen (O₂) and diluted CO₂ concentrations. By using acetonitrile as an aprotic solvent and pairing it with ethanol as a proton donor, the system effectively suppressed the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), achieving a Faradaic efficiency of over 95% at pressures above 5 bar with a silver catalyst.

Overall, this thesis demonstrates that by overcoming the technical barriers in catalyst and electrolyte engineering, CO₂RR can become a viable and energy-efficient technology for practical applications, contributing to global efforts toward carbon neutrality.