MoS₂@CNTs Heterostructures-Based (Photo)ElectroCatalysts for Enhancing Nitrogen Reduction Reaction Performance for environmentally friendly NH3 production.

Ammonia (NH3) is the most versatile zero-carbon molecule and one of the most promising carriers for renewable electricity due to its exceptional properties, such as a high gravimetric energy density of 3 kWh kg-1 and a 17.7 wt% hydrogen content compared to methylcyclohexane, methanol, and lithium-ion batteries (LiBs).1 Ammonia is also an essential feedstock for many industrial processes, including agriculture, chemical production, pharmaceuticals and synthetic fiber industries.2 The demand for ammonia has been continuously increasing, making it one of the most produced inorganic chemicals, with an annual production of ~ 500 million tons.3 Currently, industrial NH3 production still relies on the traditional Haber-Bosch process, which is fossil fuel-powered and operates under extreme conditions at high temperatures (400-500 oC) and pressures (100-200 bar).2 In the context of climate change, this process generates about 400 million tons of CO₂ annually, representing around 1.5% of global greenhouse gas emissions.3 Therefore, developing green and economical alternatives for NH3 production is critically important. Electrochemical nitrogen reduction reaction (ENRR) is a promising strategy for NH₃ synthesis, offering a simple, clean, and environmentally friendly method driven by renewable energy sources.4 However, the practical application of ENRR faces significant challenges: (i) the high energy required to split the nonpolar N₂ triple bond and (ii) the competitive hydrogen evolution reaction (HER), resulting in low NH₃ yield and Faradaic efficiency (FE).4 Recently, innovative means of addressing these hurdles have emerged with the development of effective electrocatalysts and electrochemical devices. Two-dimensional materials exhibit several interesting characteristics, including a large specific surface area, atomic-scale thickness, and an abundance of surface/edge atoms. Transition metal dichalcogenides, particularly molybdenum disulfide (MoS₂), have attracted significant research interest due to their unique advantages.4 Molybdenum is considered the main active site in Mo-based nitrogenase, a capable of fixing N₂ under ambient conditions. Additionally, MoS2 can expose large numbers of edge active sites due to the its high aspect ratio, and additional sulfur vacancies or plane defects can be easily created to induce more active centers on the large area basal plane of MoS2, thus drastically enhancing N2 adsorption and cleavage.5 Furthermore, the electronic structure of MoS2 can be effectively modified by doping with heteroatoms such as iron, which can optimize its band gap and thereby enhance the NRR activity (mimicking the nitrogenase natural enzyme). One-dimension carbon nanotubes (CNTs) are also promising due to their large surface area, excellent chemical stability, and high electrical conductivity, making them ideal supports for nanosized catalysts.5 Combining the merits of two nanoscale materials -MoS2 and CNTs- is thus expected to demonstrate higher catalytic activity with high Faraday efficiency. The objective of this project is to develop a highly effective electrocatalyst for ENRR, with MoS₂ nanosheets uniformly grown on the surface of CNTs. The thesis articulates around three main challenges: - Synthesis of large scale, high-quality, mixed-dimensionality hetero- Van der Waals materials, specifically MoS₂/CNTs, using an established, home developed bottom-up approach. - Investigation of the impact of Fe-doped MoS₂ materials (nitrogenase bio-inspired) for facilitating the spontaneous capture and electrochemical reduction of N₂ under mild conditions. - Evaluation of the electro-catalytic NRR performance of Fe-doped MoS₂ materials and assessing a benchmarking of measured ammonia yields on these materials. Up to date, the most significative amount of publications in the literature, are focused on DFT calculations and simulations; not many experimental studies have yet been conducted which is most probably related to the challenges of the fabrication of such materials. The method we developed using a bottom-up approach has not been studied and possesses both the potential for large scale implementation and the unique ability to synthesize high quality materials with atomically clean and precise interfaces, a must have and real game changer for achieving efficient catalysis.

References

(1) Hui, X. et al. Front. Chem. 2022, 10, 978078.

(2) Lu, K. et al. ACS Nano 2021, 15 (10), 16887–16895.

(3) Wang, L. et al. Joule 2018, 2, 1055–1074.

(4) Chen, S. et al. Mater. Today Nano 2022, 18, 100202.

(5) Wang, S. et al. Mater. Sci. Semicond. Process. 2024, 177, 108368.

The LPICM (Laboratoire de Physique des Interfaces et des Couches Minces) at École Polytechnique focuses on cutting-edge research in the physics of materials, particularly at the nanoscale. The lab conducts research in various fields, including nanostructures, surface physics, and quantum electronics, with applications in photodetection, sensing, polarimetry, and next-generation technologies.

The candidate, with a Master 2 Research degree in chemistry-physics or materials chemistry must have expertise in materials science, electrochemistry and catalysis. Strong interest in laboratory experiments in a controlled environment. Good experience in morphological, chemical, and structural analysis techniques will be considered an asset. Excellent written and verbal communication skills (English mandatory) and independent in writing reports. Strong team player. The candidate will have to provide all the diplomas already obtained, as well as a transcript of the marks already acquired for the two years of Master