Roles of Heterojunction and Cu Vacancies in the Au@Cu2- xSe for the Enhancement of Electrochemical Nitrogen Reduction Performance

Yujin Jeong; Gnanaprakasam Janani; Dohun Kim; Tae-Yong An; Subramani Surendran; Hyunjung Lee; Dae Jun Moon; Joon Young Kim; Mi-Kyung Han; Uk Sim

doi:10.1021/acsami.3c07947

Roles of Heterojunction and Cu Vacancies in the Au@Cu_{2- x}Se for the Enhancement of Electrochemical Nitrogen Reduction Performance

ACS Appl Mater Interfaces. 2023 Oct 5. doi: 10.1021/acsami.3c07947. Online ahead of print.

Authors

Yujin Jeong¹, Gnanaprakasam Janani¹, Dohun Kim², Tae-Yong An¹, Subramani Surendran¹, Hyunjung Lee¹, Dae Jun Moon¹, Joon Young Kim^{1

3}, Mi-Kyung Han⁴, Uk Sim^{1

3

5}

Affiliations

¹ Hydrogen Energy Technology Laboratory, Korea Institute of Energy Technology (KENTECH), 200 Hyeoksin-ro, Naju, Jeonnam 58330, Republic of Korea.
² Department of Energy Science & Engineering, Daegu Gyeongbuk Institute of Science & Technology (DGIST), Daegu 42988, Republic of Korea.
³ Research Institute, NEEL Sciences, INC., Naju, Jeollanamdo 58326, Republic of Korea.
⁴ Department of Polymer Engineering, Graduate School, Alan G. MacDiarmid Energy Research Institute & School of Polymer Science and Engineering, Chonnam National University, Gwangju 61186, Republic of Korea.
⁵ Center for Energy Storage System, Chonnam National University, Gwangju 61186, Republic of Korea.

PMID: 37795987
DOI: 10.1021/acsami.3c07947

Abstract

The utilization of hydrogen (H₂) as a fuel source is hindered by the limited infrastructure and storage requirements. In contrast, ammonia (NH₃) offers a promising solution as a hydrogen carrier due to its high energy density, liquid storage capacity, low cost, and sustainable manufacturing. NH₃ has garnered significant attention as a key component in the development of next-generation refueling stations, aligning with the goal of a carbon-free economy. The electrochemical nitrogen reduction reaction (ENRR) enables the production of NH₃ from nitrogen (N₂) under ambient conditions. However, the low efficiency of the ENRR is limited by challenges such as the electron-stealing hydrogen evolution reaction (HER) and the breaking of the stable N₂ triple bond. To address these limitations and enhance ENRR performance, we prepared Au@Cu_2-xSe electrocatalysts with a core@shell structure using a seed-mediated growth method and a facile hot-injection method. The catalytic activity was evaluated using both an aqueous electrolyte of KOH solution and a nonaqueous electrolyte consisting of tetrahydrofuran (THF) solvent with lithium perchlorate and ethanol as proton donors. ENRR in both aqueous and nonaqueous electrolytes was facilitated by the synergistic interaction between Au and Cu_2-xSe (copper selenide), forming an Ohmic junction between the metal and p-type semiconductor that effectively suppressed the HER. Furthermore, in nonaqueous conditions, the Cu vacancies in the Cu_2-xSe layer of Au@Cu_2-xSe promoted the formation of lithium nitride (Li₃N), leading to improved NH₃ production. The synergistic effect of Ohmic junctions and Cu vacancies in Au@Cu_2-xSe led to significantly higher ammonia yield and faradaic efficiency (FE) in nonaqueous systems compared to those in aqueous conditions. The maximum NH₃ yields were approximately 1.10 and 3.64 μg h^-1 cm^-2, with the corresponding FE of 2.24 and 67.52% for aqueous and nonaqueous electrolytes, respectively. This study demonstrates an attractive strategy for designing catalysts with increased ENRR activity by effectively engineering vacancies and heterojunctions in Cu-based electrocatalysts in both aqueous and nonaqueous media.

Keywords: ammonia electrosynthesis; electrochemical nitrogen reduction reaction; heterojunction; hydrogen carrier; vacancy.