In-situ reconstruction of Ni-modulated BiO2−x for boosting electrocatalytic nitrite reduction to ammonia

Ammonia (NH₃), one of the most produced chemicals worldwide, plays an indispensable role in agricultural and industrial systems. Additionally, it is a promising carbon-free energy carrier due to its high hydrogen content (17.6 wt%). Currently, industrial-scale ammonia production mainly relies on the Haber-Bosch process, which heavily relies on fossil fuels, consuming nearly 1% of global energy supply annually and emitting substantial amounts of the greenhouse gas carbon dioxide.

The electrocatalytic nitrogen reduction reaction (NRR) powered by renewable energy presents a promising alternative route. However, this process is plagued by the high activation barrier of the N≡N molecule and intense competition from the hydrogen evolution reaction (HER), which generally lead to low activity and selectivity. Therefore, researchers have turned their attention to another widespread nitrogen-containing pollutant—nitrite (NO₂⁻)—as a nitrogen source for ammonia synthesis, opening a new route of “waste-to-wealth”. The dissociation energy of the N=O bond (236 kJ/mol) is only 1/4 of that of N≡N direct cleavage, endowing the possibility to reduce the nitrite to ammonia electrochemically at high current densities, which is the basic requirement for industrialization.

Despite these advantages, NO₂⁻RR still faces two major bottlenecks in practical applications:

Insufficient proton supply: To suppress HER, the reaction is conducted in near-neutral or alkaline media, where the proton concentration is extremely low, thereby limiting the subsequent hydrogenation steps.

Weak intermediate adsorption: The adsorption of NO₂⁻ and its reaction intermediates (such as *NO and *NOH) on most catalysts remains weak, resulting in sluggish reaction kinetics.

A team of material scientists led by Jun Li from Zhengzhou University in Zhengzhou, China recently proposed an in-situ reconstruction strategy that can transform Ni-doped BiO_2-x (NiBiO_2-x) to Bi/NiBiO_2-x featuring Ni²⁺-Bi⁰ dual active sites, achieving a FE_NH3 of 94.5% at −0.6 V vs. RHE as well as a NH₃ yield rate of 225.5 µmol/mg/cm²/h at −1.0 V vs. RHE.

The team published their article in Nano Research on January 6, 2026.

“In this article, an easy strategy is developed to enhance NO₂⁻RR performance by creating Ni²⁺-Bi⁰ catalytic pairs through in-situ catalyst reconstruction. During NO₂⁻RR, the Ni²⁺ site is able to reduce water dissociation barrier, while the neighbouring Bi⁰ site facilitates NO₂⁻ adsorption and the subsequent *NO₂ dissociation. Consequently, the Ni²⁺-Bi⁰ catalytic pairs within Bi/NiBiO_2-x synergistically boost electrochemical NO₂⁻RR.” said Jun Li, senior author of the paper, professor in the College of Chemistry, State Key Laboratory of Coking Coal Resources Green Exploitation, Henan Institute of Advanced Technology, Zhengzhou University.

The research team elucidated the reconstruction pathway from NiBiO_2-x to Bi/NiBiO_2-x during NO₂⁻RR through in-situ measurements and DFT calculations: Bi⁵⁺ sites possess a lower deoxygenation barrier than Bi³⁺ sites indicating Bi⁵⁺ is more readily reduced. Crucially, reduction of a subset of Bi⁵⁺ sites to Bi⁰, forming heterostructure of Bi/NiBiO_2-x with Ni²⁺-Bi⁰ catalytic pairs. This structural transformation significantly increases the deoxygenation barrier for the remaining Bi sites, thereby inhibiting further reduction. The Ni²⁺ site is able to reduce the water dissociation barrier from 0.79 to 0.41 eV, while concurrently the Bi⁰ site can strengthen NO₂⁻ adsorption to promote *NO₂H intermediate formation. Consequently, the in-situ constructed Bi/NiBiO_2-x catalyst with Ni²⁺-Bi⁰ catalytic pairs enable an excellent NO₂⁻RR performance. The present study opens the new direction to in-situ construct high-performance electroreduction catalysts for small molecule synthesis.

Other contributors include Yangyang Zhang, Zhengkun Xie, Shixuan Ge, Peiyang Li and Zhongyi Liu from College of Chemistry, State Key Laboratory of Coking Coal Resources Green Exploitation, Henan Institute of Advanced Technology, Zhengzhou University. Xiaotian Wang from Gansu Natural Energy Institute. Zaiwang Zhao from College of Chemistry and Chemical Engineering, Inner Mongolia University. Bin Liu from Department of Materials Science and Engineering, City University of Hong Kong.

This work was financially supported by the National Natural Science Foundation of China (NSFC) (No. 22308336 and No. 22508368), the City University of Hong Kong startup fund (9020003), ITF-RTH-Global STEM Professorship (9446006), JC STEM lab of Advanced CO₂ Upcycling (9228005) and China Postdoctoral Science Foundation (GZC20241544 and 2025M771187).

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.