Metal-organic framework supported metal-oxide semiconductor hetero-nanostructures for efficient photoelectrochemical water splitting (MOFMOX)

光电化学水分解（PEC-WS）是一种将太阳能转化为化学能的极具吸引力的方法。多孔金属有机骨架（MOFs）由于其固有的结构和理化性质，是一种很有前途的光催化剂。通过适当选择有机连接剂金属离子节点和/或光活性金属-有机配合物(1)反应物吸附、局部富集和活化，(2)光吸收和(3)有效电荷分离可以被修饰并导致增强甚至更好的光催化性能。然而，由于可见光吸收有限，光生成载流子的快速重组带来的能量损失以及材料稳定性不高，在实际应用中提高mof的本征光催化效率仍然面临着重大挑战。类似的缺点也归因于金属氧化物作为PEC-WS的广泛研究材料。在慕尼黑工业大学和奥洛穆茨帕拉基大学的研究小组的合作研究项目中，我们引入了一种新的策略，通过同时解决这两组光活性材料的关键限制，通过它们的组合产生先进的光活性异质纳米结构，来提高当前的PEC-WS效率。利用一维（1D）金属氧化物半导体形态和mof提供的多功能特性，为开发用于高效PEC-WS的全新高活性光电极杂化材料打开了大门（见图1）。金属氧化物半导体（MOx）如TiO2和α-Fe2O3以一维纳米结构（纳米管、纳米棒、纳米线）的形式表现出快速、长距离的电子传递、更大的比表面积和孔体积，以及增强的光吸收和散射能力。因此，我们提出通过在1D金属氧化物纳米结构上表面选择性生长MOF薄膜来制备杂化异质纳米结构，从而产生MOF@MOx体系（MOx = TiO2和α- Fe2O3）。一般来说，MOF的多功能性能和钌修饰MOF （Ru- MOF）诱导的特定共催化效应，以及MOF薄膜沉积策略所提供的光阳极组件之间的密切界面集成，预计将协同促进提高PEC-WS效率。此外，多孔MOF薄膜将作为各种客体(G)纳米颗粒（NPs）的模板/宿主，如Au， Pt， Ag纳米颗粒和/或碳量子点（CQDs，如各种掺杂碳或石墨烯），我们预计效率将进一步提高。

Photoelectrochemical water splitting (PEC-WS) is a very attractive strategy to convert solar energy into chemical energy. Porous Metal– Organic Frameworks (MOFs) are promising photocatalysts owing to their inherent structural and physio-chemical properties. By suitable choices of organic linkers metal ion nodes and/or incorporation of photoactive metal-organic complexes (1) the reactant adsorption, local enrichment and activation, (2) the light absorption and (3) the effective charge separation can be modified and leading to enhanced and even superior photocatalytic performance. However, there are still significant challenges for improving the MOFs’ intrinsic photocatalytic catalytic efficiency for practical application due to still limited visible light absorption, energy loss associated to fast recombination of photogenerated charge carriers and low materials stability. Similar drawbacks are also attributed to the metal-oxides as the by far more widely studied materials for PEC-WS. Within this collaborative research project of the research groups at TU Munich and Palacky University Olomouc we introduce a novel strategy to enhance the current PEC-WS efficiencies by simultaneous addressing the key limitations of both these groups of photoactive materials via their combination to yield an advanced photoactive hetero-nanostructure. The exploitation of one-dimensional (1D) metal oxide semiconductor morphology and the multifunctional properties provided by the MOFs opens doors to the development of entirely new class of highly active photoelectrode hybrid materials for efficient PEC-WS (see Figure 1). Metal oxide semiconductors (MOx) like TiO2 and α-Fe2O3 in the form of 1D nanostructures (nanotubes, nanorods, nanowires) show fast and long-distance electron transport, larger surface area and pore volume, as well as enhanced light absorption and scattering capabilities in comparison with bulk counterparts. Thus, we propose fabrication of hybrid hetero-nanostructures by surface selective growing MOF thin films over the 1D metal-oxide nanostructures to yield MOF@MOx systems (MOx = TiO2 and α- Fe2O3). The multifunctional capacity of MOFs in general and the specific co-catalytic effect induced by Ruthenium modified MOFs (Ru- MOFs) in conjunction with intimate interfacial integration between the photoanode components afforded by MOF thin film deposition strategies is anticipated to synergistically contribute to enhance the PEC-WS efficiency. Furthermore, the porous MOF thin films will serve as the template/host for various guest (G) nanoparticles (NPs) such as Au, Pt, Ag nanoparticles and/or carbon quantum dots (CQDs, e.g. various doped carbon or graphene) and we anticipate a further enhancement of the efficiency.