Ammonia (NH₃) is a crucial chemical as a fertilizer and energy carrier, which is mainly produced by the traditional Haber–Bosch process that consumes hydrogen and leads to the emission of carbon dioxide. The electrochemical nitrogen reduction reaction (ENRR) is considered as an alternative method with low energy consumption and mild condition. However, the NH₃ yield and faradaic efficiency (FE) of the electrocatalyst are dominated by the competition between the hydrogen evolution reaction (HER) and NRR. In order to achieve both high catalytic activity and high selectivity, the poor-performance catalyst needs to be improved via modification engineering. For the catalysts of oxygenated compounds, introducing oxygen vacancies (OVs) into the structure can enhance the catalytic property of NRR via regulating the local electronegativity and coordination environment. In this review, recent advances in the detection, preparation and application of OVs for NRR are summarized. We focus on the generating strategies of OVs and their evaluation method, including vacuum annealing, high-temperature hydrogen reduction, wet chemical, plasma treatment, and ion-doping strategy. Finally, the opportunities and challenges towards the suitable design of OVs in oxides for NRR are highlighted.

Electrochemical carbon dioxide reduction reaction (CO₂RR) can produce value-added hydrocarbons from renewable electricity, providing a sustainable and promising approach to meet dual-carbon targets and alleviate the energy crisis. However, it is still challenging to improve the selectivity and stability of the products, especially the C₂₊ products. Here we propose to modulate the electronic structure of copper oxide (CuO) through lattice strain construction by zinc (Zn) doping to improve the selectivity of the catalyst to ethylene. Combined performance and in situ characterization analyses show that the compressive strain generated within the CuO lattice and the electronic structure modulation by Zn doping enhances the adsorption of the key intermediate ^⋆CO, thereby increasing the intrinsic activity of CO₂RR and inhibiting the hydrogen precipitation reaction. Among the best catalysts had significantly improved ethylene selectivity of 60.5% and partial current density of 500 mA·cm⁻², and the highest C₂₊ Faraday efficiency of 71.47%. This paper provides a simple idea to study the modulation of CO₂RR properties by heteroatom doped and lattice strain.

The electrochemical nitrate reduction reaction (NO₃RR) to ammonia under ambient conditions is a promising approach for addressing elevated nitrate levels in water bodies, but the progress of this reaction is impeded by the complex series of chemical reactions involving electron and proton transfer and competing hydrogen evolution reaction. Therefore, it becomes imperative to develop an electro-catalyst that exhibits exceptional efficiency and remarkable selectivity for ammonia synthesis while maintaining long-term stability. Herein the magnetic biochar (Fe-C) has been synthesized by a two-step mechanochemical route after a pyrolysis treatment (450, 700, and 1000 °C), which not only significantly decreases the particle size, but also exposes more oxygen-rich functional groups on the surface, promoting the adsorption of nitrate and water and accelerating electron transfer to convert it into ammonia. Results showed that the catalyst (Fe-C-700) has an impressive NH₃ production rate of 3.5 mol·h⁻¹·g_cat⁻¹, high Faradaic efficiency of 88%, and current density of 0.37 A·cm⁻² at 0.8 V vs. reversible hydrogen electrode (RHE). In-situ Fourier transform infrared spectroscopy (FTIR) is used to investigate the reaction intermediate and to monitor the reaction. The oxygen functionalities on the catalyst surface activate nitrate ions to form various intermediates (NO₂, NO, NH₂OH, and NH₂) and reduce the rate determining step energy barrier (*NO₃ → *NO₂). This study presents a novel approach for the use of magnetic biochar as an electro-catalyst in NO₃RR and opens the road for solving environmental and energy challenges.