Mo2C-MoO2 Heterostructure Quantum Dots for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

Yuchi Wan; Zhijie Wang; Jia Li; Ruitao Lv

doi:10.1021/acsnano.1c07973

Mo₂C-MoO₂ Heterostructure Quantum Dots for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

ACS Nano. 2022 Jan 25;16(1):643-654. doi: 10.1021/acsnano.1c07973. Epub 2021 Dec 29.

Authors

Yuchi Wan¹, Zhijie Wang², Jia Li^{2

3}, Ruitao Lv^{1

4}

Affiliations

¹ State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
² Shenzhen Geim Graphene Center and Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
³ Guangdong Provincial Key Laboratory of Thermal Management Engineering and Materials, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
⁴ Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.

PMID: 34964347
DOI: 10.1021/acsnano.1c07973

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising strategy for producing ammonia (NH₃) at ambient conditions. However, the development of the NRR is severely hindered by the difficult adsorption and activation of N₂ on the catalyst surface and the competitive hydrogen evolution reaction (HER) due to the lack of efficient NRR electrocatalysts. Herein, Mo₂C-MoO₂ heterostructure quantum dots embedded in reduced graphene oxide (RGO) are proposed as efficient catalysts for the electrocatalytic NRR. The ultrasmall size of the quantum dot is beneficial for exposing the active sites for the NRR, and the synergetic effect of Mo₂C and MoO₂ can promote N₂ adsorption and activation and suppress the competitive HER simultaneously. As a result, a well-balanced NRR performance is achieved with a high NH₃ yield rate of 13.94 ± 0.39 μg h^-1 mg^-1 at -0.15 V vs RHE and a high Faradaic efficiency of 12.72 ± 0.58% at -0.1 V vs RHE. Density functional theory (DFT) calculations reveal that the Mo₂C (001) surface has a strong N₂ adsorption energy of -1.47 eV with the side-on configuration, and the N≡N bond length is elongated to 1.254 Å, indicating the enhanced N₂ adsorption and activation on the Mo₂C surface. On the other hand, the low ΔG_H* for HER over the MoO₂ (-111) surface demonstrates the impeded HER process for MoO₂. This work may provide effective catalyst-design strategies for enhancing the electrocatalytic NRR performance of Mo-based materials.

Keywords: Mo2C-MoO2 heterostructure; ammonia synthesis; electrocatalysis; nitrogen reduction reaction; quantum dots.