Oral Presentation Royal Australian Chemical Institute National Congress 2026

Regulating *NO hydrogenation pathways for selective hydroxylamine electrosynthesis from nitrate on intermetallic Cu3Sn (138102)

Zhi-Xuan Wu 1 , Shujie Zhou 1 , Cui Ying Toe 2 , Jodie Yuwono 3 , Yufei Zhao 4 , Rose Amal 1
  1. University of New South Wales, Kensington, NSW, Australia
  2. School of Engineering, University of Newcastle, New Castle, NSW, Australia
  3. Chemical Engineering, Adelaide University, Adelaide, SA, Australia
  4. School of Mathematical and Physical Sciences, University of Technology Sydney, Sydney, NSW, Australia

Hydroxylamine (NH2OH) is a vital nitrogenous feedstock in the chemical industry, but its conventional production relies on energy-intensive processes involving explosive gases and corrosive chemicals.1 Recently, electrochemical nitrate reduction (NO3RR) powered by renewable energy has emerged as a sustainable alternative under mild conditions.2 However, the direct electrosynthesis of NH2OH remains challenging because NO3RR proceeds through complex proton-coupled electron transfer pathways, and NH2OH typically exists as a transient intermediate toward ammonia (NH3).3

 

While considerable research has been devoted to improving NH2OH selectivity 4-6, the mechanistic role of hydrogenation pathways remains unclear. In this work, we employ an intermetallic Sn-Cu catalyst supported on Cu foam (Sn-Cu/CF) to investigate the underlying *NO hydrogenation pathways and the role of proton availability in the electrosynthesis of NH2OH. Sn-Cu/CF achieves a Faradaic efficiency (FE) of 70% at -0.75V vs RHE (pH~2), distinctly outperforming CF.

 

Electrochemical measurements combined with in situ FTIR and density functional theory (DFT) calculations reveal that the selectivity for NH2OH is governed by the two-step *NO hydrogenation. The intermetallic Sn-Cu/CF is thermodynamically favorable to stabilize the N-end protonation (*NHO and *NH2O), which sustains the N-O bond retention and subsequently promotes *NH2OH formation. In contrast, N-O cleavage more readily occurs through the O-end protonation pathways via *NHOH, subsequently shifting selectivity to NH4+.

 

Furthermore, the pH-dependent NO3RR and DFT reveal a dual role of proton availability: sufficient proton supply facilitates the N-end protonation at the first step of *NO hydrogenation, but excessive protons would intensify the O-end protonation at the second step, leading to excessive hydrogenation into NH4+. These findings establish the *NO hydrogenation pathway control and proton regulation as key mechanistic descriptors for selective NH2OH electrosynthesis from nitrate, providing mechanistic insights for future rational design of catalysts and reaction conditions.

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