A first principle investigation on carbon-based catalyst for nitrogen reduction reaction

• Main Author: Pranoto, Kevin
• Other Authors: Li Shuzhou
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/165769
• Institution: Nanyang Technological University

Ammonia (NH3) has played a significant role as a fertilizer to exponentially increase food productivity for the population, making it one of the most significant gases employed in human histories. Demand for NH3 has reached its peak ever as more cutting-edge clean renewable energy technologies look to utilize its high volumetric energy density for its potential as a fuel and low-cost grid-level scale energy storage solution. Because the Haber-Bosch process continues to be extremely energy-intensive and produces enormous amounts of greenhouse gas every day, solutions to NH3 production have been extensively sought after. Electrocatalyst synthesis of NH3 is a promising process in solving the energy cost of Haber-Bosch process. One distinguished method in NH3 synthesis is nitrogen reduction reaction (NRR). NRR consist of three basic steps: adsorption of nitrogen gas, hydrogenation, and desorption. However, even with numerous progresses in NRR, the targets of industrialized NRR are still far away because of the parasitic hydrogen evolution reaction (HER). HER is a massive problem to NRR due to its low energy barrier, which in turn take away needed energy for NRR. To improve the selectivity of NH3, various attempts on catalytic surfaces has been done to lower the overpotential of NRR for better competing performance. In this paper, we will explore another path in tackling this problem by prohibiting the HER performance with carbon-based catalyst, specifically TiC. TiC is known to have a much stronger H* binding energy, which is not an typical HER catalyst. To enhance this feature even further, we doped TiC surface with 3d-transition metal to improve the strength of N* binding. Here, we investigated the effect of TiC (111) surface, both pure and doped surface, as a NRR electrocatalyst. The results that we got shows the limiting potential of NRR on TiC (111) as -1.25 V while HER is -1.69 V. Which means NRR are more likely to occur on TiC (111) surface compared to HER. After that, using 3d-transition metal as dopant, we found out that it reduces limiting potential of HER drastically, averaging at -1.96V. NRR value also reduces but by a small amount, averaging at -1.29 V. This results in more ammonia created on the surface. With this, it can be concluded that using 3d-transition metal to dope TiC surface would improve the performance of NRR compared to HER.