氨是一种重要的工业原料,也是一种潜在的绿色能源,在环境条件下利用可再生能源将氮气还原合成氨是一种有吸引力的方法,但是开发高效光电化学合成氨的催化剂仍然是一个挑战。在此,采用两步法制备BaSrTiO₃,并用管式炉煅烧将Pt纳米颗粒修饰在BaSrTiO₃上制备Pt@BaSrTiO₃。采用XRD、BET、XPS、SEM、TEM、UV-Vis和PL进行表征,分析所得催化剂的晶体结构、形貌和光学性能。研究BaSrTiO₃和Pt@BaSrTiO₃在常温常压下光电化学合成氨性能。结果表明Pt@BaSrTiO₃在-0.3 V（vs. RHE）电位下合成氨的产率为26.57 × 10^-8 mol·h^-1·mg^-1,是纯BaSrTiO₃的2倍（13.12 × 10^-8 mol·h^-1·mg^-1）。另外,Pt@BaSrTiO₃作为催化剂在-0.3 V（vs. RHE）的法拉第效率为5.43%。通过在BaSrTiO₃上修饰Pt,增加催化剂的活性位点。修饰Pt减小催化剂的带隙,可见光吸收范围增大。此外, Pt-BST异质结结构进一步增强电荷分离和转移,抑制电子-空穴对的复合从而提高电荷分离效率。这项工作为进一步设计钙钛矿催化剂来提高氨的产率提供了良好的思路。

Ammonia is an important industrial raw material and a potential green energy. Using renewable energy to convert nitrogen into ammonia under ambient condition is an attractive method. However, the development of efficient photoelectrochemical ammonia synthesis catalysts remains a challenge. Perovskite such as BaSrTiO₃ (BST) is a good photocatalytic material. However, BST is active under ultraviolet light and has a high recombination rate of photogenerated electron-hole pairs. By dispersing precious metals, it can effectively regulate the absorption of sunlight by BST. In this work, we used a two-step method to prepare BST. The H₂PtCl₆·6H₂O solution was dispersed on the BST, and then followed by calcination in a tube furnace to obtain Pt@BaSrTiO₃ (Pt@BST). X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were utilized to analyze the structures, morphologies, and surface chemical composition of the synthesized materials. Results showed that the well-crystallized Pt particles were successfully loaded onto the BST surface, and Pt and BST interacted to produce a metal-semiconductor heterojunction, improving the performance of N₂ reduction. The N₂ adsorption and desorption isotherms showed that the increase in the specific surface area helped the catalyst to adsorb N₂, and the contact area with H₂O also increased, which promotes the occurrence of NRR and thus produces more NH₃. UV-Vis and PL spectroscopic techniques were used to characterize and analyze optical properties of the obtained catalyst. It is indicated that decoration of Pt reduces the band gap of the catalyst and increases the visible light absorption range, in addition, further enhances the charge separation and transfer, inhibits the recombination of electron-hole pairs, and improves the efficiency of charge separation. The performances of BST and Pt@BST for photoelectric catalytic synthesis of ammonia under ambient condition were studied. The yield of ammonia first increased and then decreased with the increase of Pt content. When the Pt content was 4wt%, the yield was the highest. The results showed that the ammonia yield of Pt@BST was 26.57 × 10^-8 mol·h^-1·mg^-1 and Faraday efficiency (FE) was 5.43% at -0.3 V (vs. RHE) in 0.1 mol·L^-1 Na₂SO₄ under natural conditions, suggesting that the ammonia yield of Pt@BST was twice that of pure BST (13.12 × 10^-8 mol·h^-1·mg^-1). We conducted control experiments of ¹⁵N₂ isotope and Ar in order to eliminate internal and external environmental pollution. Confirming that the detected NH₃ was produced exclusively via nitrogen reduction reaction. After recycling the test six times at -0.3 V (vs. RHE), both FE and ammonia yield rate showed a slight variation, indicating the high stability of Pt@BST during N₂ reduction process. This work provides a simple strategy for further designing the preparation of noble metal modified perovskite catalysts, and has promising application prospects in ammonia synthesis under ambient condition.