| Abstrakt: |
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 x 10-8 mol⋅h-1⋅mg-1 and Faraday efficiency (FE) was 5.43% at -0.3 V (vs. RHE) in 0.1 mol⋅-1 Na2SO4 under natural conditions, suggesting that the ammonia yield of Pt@BST was twice that of pure BST (13.12 x 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. [ABSTRACT FROM AUTHOR] |
