Interfacial Engineering Boosts the Electrocatalytic Ammonia Synthesis of Rhodium Catalyst

Jun 24, 2022 | By JIN Meng

A research team led by Prof. ZHANG Haimin from the Institute of Solid State Physics, Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS) reported their finding of dodecanethiol-modified metallic rhodium (Rh) for high-performance electrocatalytic nitrogen (N2) to ammonia (NRR).

After pyrolysis for 0.5 h at 150 ℃, the obtained electrode through an interfacial engineering approach exhibited an excellent NRR activity with an ammonia yield rate of 121.2 ± 6.6 μg h-1 cm-2 (or 137.7 ± 7.5 μg h-1 mgRh-1) and a faradaic efficiency of 51.6 ± 3.8 % at –0.2 V (vs. RHE) in 0.1 M Na2SO4.

This result was published in Nano Research.

Compared with the Haber-Bosch process with harsh reaction conditions and high energy consumption, the electrocatalytic NRR can be carried out at room temperature and pressure, and water is the source of hydrogen. Therefore, it is of great scientific research value and industrial application feasibility.

However, the non-dipole and low solubility of nitrogen make it difficult to adsorb on the catalyst surface and be activated, and the reaction site was more likely to be occupied by protons generated by water splitting, resulting in lower Faradaic efficiency and yield.

The dodecanethiol modified Rh in this study was fabricated via a facile saturated dodecanethiol vapor-phase hydrothermal reaction followed by a low-temperature pyrolysis process. The hydrophobic dodecanethiol molecules on the surface of Rh created a stereo-hindrance effect, which inhibited the diffusion of water molecules or H+ to the metal surface and facilitated N2 adsorption, thus improving the NRR selectivity.

Furthermore, density-functional-theory calculations unveiled that the surface hydrogen coverage and the NRR reaction energy barrier were both decreased after dodecanethiol modification, thereby greatly enhancing the NRR performance.

The interfacial engineering approach used in this work would be very helpful for developing high-efficiency NRR electrocatalysts to synthesize ammonia under ambient conditions. It provided new insights into the effect of the metal-organic interface and H* coverage on the electrochemical NRR activity.

This work was supported by the This work was financially supported by the Natural Science Foundation of China (grant no. 51872292), the young project of Anhui Provincial Natural Science Foundation (grant no. 1908085QB83).

Illustration of the research (Image by JIN Meng)

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