Tungsten Nitride/Tungsten Oxide Nanosheets for Enhanced Oxynitride Intermediate Adsorption and Hydrogenation in Nitrate Electroreduction to Ammonia

Zhencong Huang; Baopeng Yang; Yulong Zhou; Wuqing Luo; Gen Chen; Min Liu; Xiaohe Liu; Renzhi Ma; Ning Zhang

doi:10.1021/acsnano.3c07734

Tungsten Nitride/Tungsten Oxide Nanosheets for Enhanced Oxynitride Intermediate Adsorption and Hydrogenation in Nitrate Electroreduction to Ammonia

ACS Nano. 2023 Dec 26;17(24):25091-25100. doi: 10.1021/acsnano.3c07734. Epub 2023 Dec 6.

Authors

Zhencong Huang¹, Baopeng Yang², Yulong Zhou¹, Wuqing Luo¹, Gen Chen¹, Min Liu², Xiaohe Liu³, Renzhi Ma⁴, Ning Zhang¹

Affiliations

¹ School of Materials Science and Engineering, Central South University, Changsha 410083, China.
² School of Physics and Electronics, Central South University, Changsha 410083, China.
³ School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China.
⁴ Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.

PMID: 38054420
DOI: 10.1021/acsnano.3c07734

Abstract

Electrochemical NO₃^- reduction reaction (NO₃RR) is a promising technique for green NH₃ synthesis. Tungsten oxide (WO₃) has been regarded as an effective electrocatalyst for electrochemical NH₃ synthesis. However, the weak adsorption and the sluggish hydrogenation of oxynitride intermediates (NO_x, e.g., *NO₃ and *NO₂) over WO₃ materials hinder the efficiency of converting NO₃^- to NH₃. Herein, we design a heterostructure of tungsten nitride (WN) and WO₃ (WN/WO₃) nanosheets to optimize *NO₃ and *NO₂ adsorptions and facilitate *NO₂ hydrogenations to achieve a highly efficient electrochemical NO₃RR to produce NH₃. Theoretical calculations predict that locally introducing WN into WO₃ will shorten the distance between adjacent W atoms, resulting in *NO₃ and *NO₂ being strongly adsorbed on W active sites in the form of bidentate ligands instead of the relatively weak monodentate ligands. Furthermore, WN facilitates H₂O dissociation to supply the requisite protons, which is beneficial for *NO₂ hydrogenations. Inspired by theoretical prediction, WN/WO₃ nanosheets are successfully fabricated through a high-temperature nitridation process. The transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy investigations confirm that the amorphous WN has been locally introduced in situ into WO₃ nanosheets to form a composite heterostructure. The as-prepared WN/WO₃ nanosheets exhibit a high Faraday efficiency of 88.9 ± 7.2% and an appreciable yield rate of 8.4 mg h^-1 cm^-2 toward NH₃ production, which is much higher than that of individual WO₃ and WN. The enhanced adsorption and hydrogenation behaviors of *NO_x over WN/WO₃ are characterized by in situ Fourier-transform infrared spectroscopy, consistent with the theoretical predictions. This work develops facile and effective heterostructure nanomaterials to tune the adsorption and hydrogenation of NO_x for boosting the efficiency from NO₃^- to NH₃.

Keywords: adsorption configuration; ammonia synthesis; composite structure; nitrate reduction reaction; tungsten nitride; tungsten oxide.