Catalyst Engineering and Mechanistic Insights into Electrochemical NOx Conversion in PEM Electrolyzer
M. Li (TU Delft - ChemE/Catalysis Engineering)
A. Urakawa – Promotor (TU Delft - ChemE/Catalysis Engineering)
R. Kortlever – Promotor (TU Delft - Large Scale Energy Storage)
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Abstract
The transition to zero-carbon fertilizers challenges conventional ammonia production via the Haber-Bosch process. Electrochemical ammonia synthesis offers a sustainable alternative using only water, electricity, and nitrogen from waste streams such as nitrate and NOx. This dissertation employs a polymer electrolyte membrane (PEM) electrolyzer and addresses key cost and efficiency drivers through catalyst design, mechanistic analysis, and cell-level engineering.
Ru/C catalysts were optimized with polyvinylpyrrolidone (PVP), reducing Ru loading from 40 to 10 wt.% while enhancing NH₃ faradaic efficiency, electrochemical surface area, hydrogen binding, and wettability. Earth-abundant MoS₂ catalysts were phase-engineered to steer proton-electron transfer pathways for selective NO reduction. A CO-mediated poisoning strategy was developed to suppress the competing hydrogen evolution reaction, improving NH₃ selectivity.
Proof-of-concept C–N coupling for urea synthesis from bicarbonate and nitrate was demonstrated using gas-diffusion electrodes. Finally, a novel operando ATR-IR cell was designed to probe reaction mechanisms under realistic conditions, bridging the gap between batch-cell studies and PEM electrolyzer operation.