论文部分内容阅读
助剂修饰是提高单相光催化剂催化制氢活性的有效策略之一.贵金属Pt是光催化制氢体系中较为理想的助催化剂,但价格高、储量少,严重限制了其广泛应用.在过去几十年中,研究者研发了一系列低成本的非Pt助催化剂,如金属氧化物、碳化物、氮化物、硫化物和磷化物等,并应用于光催化制氢,但其催化活性与Pt助催化剂相比有较大差距.近年来,与Pt具有相似的物化性质,但价格较低的其他铂族金属得到了广泛关注和研究.贵金属Pd不仅具有良好的导电性和稳定性,而且相对于Pt,Pd的储量更丰富且廉价(Pd:124.9元/克,Pt:224.8元/克),因而被认为是一种很有应用前景的析氢助催化剂.然而,Pd金属助剂在实际应用中的析氢活性并不理想,主要是因为Pd对氢原子(H)的吸附强度过高,严重限制了后续的氢脱附过程,导致材料整体的析氢反应速率较慢.因此,发展合适的方法来优化Pd的电子结构以弱化其对氢的吸附强度,对进一步提升Pd助剂的催化析氢活性具有重要意义.本文通过一种简易的NaH2PO2介导的共沉积策略,成功地将过渡金属Cu引入金属Pd的晶格中,并通过Pd-Cu合金化作用弱化了Pd对氢的吸附强度,进而有效提高界面H2释放速率.通过X射线衍射、高分辨率透射电镜、X射线光电子能谱和电感耦合等离子体等技术对Pd100-xCux合金的结构和形貌进行了分析.结果表明,Pd100-xCux合金纳米点(2-5 nm)成功修饰于TiO2表面,所得的Pd100-xCux/TiO2光催化剂表现出显著增强的光催化制氢性能.其中,Pd75Cu25/TiO2样品的催化性能达到269.2μmol h-1,是纯TiO2的90倍.此外,原位X射线光电子能谱和密度泛函理论的结果表明,所形成的Pd100-xCux合金纳米点因其自身优异的导电性可以有效促进光生电荷的分离;同时,Cu的成功引入弱化了Pd对氢的吸附强度,从而促进了Pd75Cu25合金上的氢解吸过程,最终有效提升了光催化剂的制氢活性.Pd75Cu25合金对H吸附强度降低的原因是:引入弱电负性的Cu元素后,Cu的部分电子转移至Pd上形成富电子的Pd,进而降低了Pd对H的吸附强度.本文通过优化电子结构以促进界面反应活性的策略为开发高效光催化剂提供了新的见解.“,”Noble metal palladium (Pd) is well-known as excellent photocatalytic cocatalyst, but its strong ad-sorption to hydrogen causes its limited H2-evolution activity. In this study, the transition metal Cu was successfully introduced into the metallic Pd to weaken its hydrogen-adsorption strength to improve its interfacial H2-evolution rate via the Pd-Cu alloying effect. Herein, the ultrasmall Pd100-xCux alloy nanodots (2-5 nm) as a novel H2-evolution cocatalyst were integrated with the TiO2 through a simple NaH2PO2-mediated co-deposition route. The resulting Pd100-xCux/TiO2 sample shows the significantly enhanced photocatalytic H2-generation performance (269.2 μmol h-1), which is much higher than the bare TiO2. Based on in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and density functional theory (DFT) results, the as-formed Pd100-xCux alloy nanodots can effectively promote the separation of photo-generated charges and weak the adsorption strength for hydrogen to optimize the process of hydrogen-desorption process on Pd75Cu25 alloy, thus lead-ing to high photocatalytic H2-evolution activity. Herein, the weakened H adsorption of Pd75Cu25 co-catalyst can be ascribed to the formation of electron-rich Pd after the introduction of weak electro-negativity Cu. The present work about optimizing electronic structure for promoting interfacial reaction activity provides a new sight for the development of the highly efficient photocatalysts.