Interfacial coordination bonds accelerate charge separation for unprecedented hydrogen evolution over S-scheme heterojunction

界面配位键加速S型异质结电荷分离用于高效光催化析氢

Inspired by natural photosynthesis,fabricating high-performance S-scheme heterojunction is regarded as a successful tactic to address energy and environmental issues.Herein,NH_(2)-MIL-125(Ti)/Zn_(0.5)Cd_(0.5)S/NiS(NMT/ZCS/NiS)S-scheme heterojunction with interfacial coordination bonds is successfully synthesized through in-situ solvothermal strategy.Notably,the optimal NMT/ZCS/NiS S-scheme heterojunction exhibits comparable photocatalytic H_(2)evolution(PHE)rate of about 14876.7μmol h^(−1)g^(−1)with apparent quantum yield of 24.2%at 420 nm,which is significantly higher than that of recently reported MOFs-based photocatalysts.The interfacial coordination bonds(Zn–N,Cd–N,and Ni–N bonds)accelerate the separation and transfer of photogenerated charges,and the NiS as cocatalyst can provide more catalytically active sites,which synergistically improve the photocatalytic performance.Moreover,theoretical calculation results display that the construction of NMT/ZCS/NiS S-scheme heterojunction also optimize the binding energy of active site-adsorbed hydrogen atoms to enable fast adsorption and desorption.Photoassisted Kelvin probe force microscopy,in-situ irradiation X-ray photoelectron spectroscopy,femtosecond transient absorption spectroscopy,and theoretical calculations provide sufficient evidence of the S-scheme charge migration mechanism.This work offers unique viewpoints for simultaneously accelerating the charge dynamics and optimizing the binding strength between the active sites and hydrogen adsorbates over S-scheme heterojunction.

随着经济社会的高速发展,环境污染和能源匮乏等问题日益突出,建立清洁、高效的能源体系和实现绿色可持续的社会发展已成为目前科学研究的热点.氢能是零污染的清洁能源,加快发展氢能产业,有望从根本上实现能源可持续发展.当今社会,制备氢气的途径有很多,但从绿色化学的角度,光催化制氢是较为理想的制氢途径之一.为了加快光催化技术的发展,高效光催化剂的设计和构建便尤为重要.目前,光生载流子分离效率低是限制高效光催化材料发展的重要因素,然而,界面配位键的合理构建是提升光生电子-空穴对分离和迁移效率的重要手段之一。本文通过水热法和原位合成法制备了具有界面配位键的NH_(2)-MIL-125(Ti)/Zn_(0.5)Cd_(0.5)S/NiS(NMT/ZCS/NiS)S型异质结;通过X射线衍射(XRD)、扫描电镜、透射电镜以及X射线光电子能谱(XPS)等系列表征证明了光催化剂的成功制备.在可见光下,最优比例光催化剂30%NMT/ZCS/2%NiS(30%代表NMT占ZCS/2%NiS的质量百分比;2%代表NiS占ZCS的质量百分比)的光催化析氢速率约为14876.7μumolhg,其性能优于大部分报道的MOFs基光催化剂.此外,在420nm的单色光照射下,表观量子产率(AQY)可达到24.2%.在该体系中,首先,Zn-N,Cd-N和Ni-N界面配位键的存在加速了光生载流子的分离和转移.其次,NiS作为助催化剂也为光催化材料提供了更多的催化活性位点.界面配位键的存在和NiS作为助催化剂协同提高了光催化析氢性能.而且,NiS与ZCS之间高度匹配的晶格常数也赋予该S型异质结更多的催化活性位点和更快的光载流子分离速率此外,理论计算结果表明,该S型异质结的成功构建也可从热力学角度加快催化反应的进行.光辅助开尔文探针力显微镜、原位XPS、飞秒瞬态吸收光谱和理论计算结果共同揭示了S型电荷迁移机理。在可见光照射条件下,NMT导带上累积的光生电子与ZCS价带上累积的光生空穴发生复合.随后,ZCS导带上的电子继续向NiS助催化剂上迁移,富含电子的NiS充当活性位点并提供电子来激活H,O生成H_(2).更为重要的是,Zn-N,Cd-N和Ni-N界面配位键作为载流子传输桥极大抑制了光生电子-空穴对的重组,加快了光催化析氢反应的进行。除催化活性外,光催化材料的化学稳定性也尤为重要,本文通过XRD,XPS以及光催化析氢循环实验证明了其化学稳定性.高效的光催化活性和较好的化学稳定性为该催化剂后续工业应用提供了广阔的前景。综上所述,该体系光催化析氢性能的提升可归因于界面配位键(Zn-N,Cd-N和Ni-N键)的形成,此外,S型异质结的形成也可同时从动力学和热力学角度加快光催化反应的进行.本文为开发具有界面配位键的高效稳定的MOFs/Zn,Cdi-rS基光催化剂提供了参考.