【Domestic Papers】Interface Hydrophobic Engineering on Copper Species-Modified Ga₂O₃ Nanofibers for Enhanced Nitrate Electroreduction

      Researchers from the Donghua University have published a dissertation titled "Interface Hydrophobic Engineering on Copper Species-Modified Ga₂O₃ Nanofibers for Enhanced Nitrate Electroreduction" in Advanced Functional Materials.

Project Support

      This work was supported by the Fundamental Research Funds for the Central Universities (No. 2232025A-07), the National Natural Science Foundation of China (No. 52503378), the Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission (No. 24CGA66), the Program of Shanghai Academic Research Leader (No. 23XD1400100), and the Natural Science Foundation of Shanghai (No. 23ZR1401400).

Background

      The nitrogen cycle plays a critical role in maintaining ecological balance; however, intensive human activities, such as excessive fertilizer use and industrial emissions, have severely disrupted this cycle, leading to nitrate accumulation in aquatic environments and posing significant risks to ecosystems and public health. Conventional nitrate removal technologies suffer from inherent limitations, including sluggish kinetics, high energy consumption, and the generation of undesirable by-products. In contrast, electrocatalytic nitrate reduction to ammonia (NO₃RR-to-NH₃) offers a promising and sustainable alternative by simultaneously achieving nitrate remediation and producing ammonia, a valuable carbon-free energy carrier and chemical feedstock.

      Despite its advantages, NO₃RR is a complex multielectron–multiproton process, and its practical application is hindered by the difficulty of developing electrocatalysts with simultaneously high activity, selectivity, and long-term stability. This challenge becomes particularly pronounced under low nitrate concentrations, where the competing hydrogen evolution reaction (HER) significantly suppresses Faradaic efficiency. Solely relying on intrinsic catalyst structure optimization is often insufficient to balance HER suppression and NO₃RR enhancement, prompting increasing interest in interface engineering strategies to regulate the reaction microenvironment.

      In this work, a dual synergistic strategy integrating electronic structure modulation and interfacial microenvironment regulation is proposed. Copper species and oxygen vacancies are in situ generated on Ga₂O₃ nanofibers via hydrogen thermal reduction, effectively tuning the electronic structure and enhancing the activation of both nitrate species and adsorbed hydrogen intermediates (H*). Meanwhile, a low-surface-energy self-assembled monolayer is introduced to construct a hydrophobic interface, which regulates proton availability, suppresses HER, and promotes preferential nitrate adsorption. Benefiting from this cooperative design, the resulting r-Cu/Ga₂O₃-SAM catalyst delivers an exceptionally high ammonia yield rate and Faradaic efficiency under low nitrate concentrations, demonstrating significantly improved performance for electrocatalytic nitrate reduction to ammonia.

Abstract

      Suppressing the competing hydrogen evolution reaction (HER) and inefficient mass transport remains a major obstacle for electrocatalytic nitrate reduction reactions (NO₃RR), particularly in low-nitrate-concentration industrial wastewater. Nevertheless, previous studies have primarily focused on optimizing intrinsic catalyst activity, yet achieving high selectivity and activity simultaneously remains challenging. Herein, we report a dual-coordination strategy to modulate the surface electronic structure and interfacial microenvironment of nanofiber catalysts, thereby enabling simultaneous HER suppression and enhanced electrocatalytic activation of nitrate (NO₃⁻).

      Specifically, a reduced copper species–modified gallium oxide (r-Cu/Ga₂O₃) nanofiber catalyst with abundant Cu species and oxygen vacancies is obtained via thermal reduction of the oxide precursor through an in situ exsolution method, which significantly enhances nitrate adsorption and activation. Moreover, a low-surface-energy monolayer interface is assembled on the nanofiber surface to regulate the reaction microenvironment, restricting proton transfer to active sites and kinetically inhibiting HER.

      As a result, the prepared r-Cu/Ga₂O₃–SAM nanofiber catalyst achieves an NH₃ yield of 22.36 mg h⁻¹ mg⁻¹ at −1.15 V and a Faradaic efficiency (FE) of 95.48% at −1.05 V versus the reversible hydrogen electrode (RHE) in a 20 mM NO₃⁻ solution. We expect that these findings will provide new insights and practical guidance for the rational design of efficient electrocatalytic NO₃RR catalysts under low NO₃⁻ concentration conditions.

Conclusion

      To summarize, we have successfully achieved the concurrent enhancement of electrocatalytic nitrate reduction reactions (NO₃RR) and suppression of the competing hydrogen evolution reaction (HER) via a synergistic strategy that modulates both the electronic structure and interfacial microenvironment of the nanofiber catalyst. Specifically, r-Cu/Ga₂O₃ nanofibers were designed as efficient electrocatalysts for NO₃RR through in situ metal deposition enabled by thermal reduction of metal oxides. The optimized electronic states, arising from increased oxygen vacancies (Oᵥ) and enriched Cu species on the catalyst surface, serve as pivotal factors in facilitating electrocatalytic NO₃RR.

      Furthermore, the construction of a low-surface-energy self-assembled monolayer (SAM) on the r-Cu/Ga₂O₃ nanofibers effectively alters the interfacial microenvironment, elevating the energy barrier for HER and thereby improving the Faradaic efficiency (FE) of NO₃RR. Benefiting from this synergistic strategy, the r-Cu/Ga₂O₃–SAM nanofiber catalyst delivers an NH₃ yield of 22.36 mg h⁻¹ mg⁻¹ at −1.15 V and achieves a FE of 95.48% at −1.05 V versus the reversible hydrogen electrode (RHE) in a 20 mM NO₃⁻ solution.

      This study is expected to provide novel insights into the systematic design of both electronic structure and interfacial microenvironment of electrocatalysts for the efficient treatment of low-concentration industrial wastewater.