| Facet-Selective Bromide Adsorption at High-index Facets of Copper Sulfides for Improved Electrochemical Nitrogen Reduction Activity and Selectivity |
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Gyu Seong Yi1,2, Bohyun Jo3, Yung-Eun Sung2,4, Taekyung Yu3, Hyun S. Park1,5 |
1Center for Hydrogen-Fuel Cell Research, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea
2School of Chemical and Biological Engineering, Seoul National University (SNU), Seoul, Republic of Korea
3Department of Chemical Engineering, Integrated Engineering Major, Kyung Hee University (KHU), Yongin, Republic of Korea
4Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, Republic of Korea
5Division of Energy & Environment Technology, KIST School, University of Science and Technology (UST), Seoul, Republic of Korea |
Correspondence:
Hyun S. Park, Tel: +82-2-958-5250,
Email: hspark@kist.re.kr
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Received: 7 May 2025 • Accepted: 5 July 2025 |
| Abstract |
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Electrochemical nitrogen reduction reaction (eNRR) is a promising sustainable alternative to the energy-intensive Haber–Bosch process for ammonia (NH₃) synthesis. However, simultaneously achieving high activity and selectivity remains challenging due to competing hydrogen evolution reaction (HER). In this study, a series of copper sulfide catalysts were investigated for eNRR under ambient conditions. Copper sulfides featuring highly crystalline low-index (1 1 1) facets exhibited significant NH₃ production; however, the presence of high-index facets led to a reduction in Faradaic efficiency (F.E.) due to their higher activity toward the competing HER. To mitigate this intrinsic trade-off between activity and selectivity, bromide ions were introduced to selectively adsorb onto the high-index planes, effectively suppressing HER. Optimizing the bromide ion coverage on CuSₓ catalysts resulted in a maximum NH3 yield of 1.2 μmol h–¹ cm–² (JNH3 = 0.198 mA/cm2) and a F.E. of 23.34% at −0.6 VRHE, marking improvements of 84.0% in activity and 316% in selectivity compared to untreated catalysts. It was verified that bromide ions selectively passivate HER-prone surfaces without blocking the active sites responsible for nitrogen adsorption. This study highlights that facet-selective surface engineering using halide ions can simultaneously enhance both activity and selectivity in eNRR. It provides a rational design principle for improving catalytic performance in complex reaction environments where multiple pathways compete. |
| Keywords:
Electrochemical nitrogen reduction reaction (eNRR), Facet-selective adsorption, Copper sulfide, Hydrogen evolution reaction (HER) inhibitor |
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