Ferrites for photoelectrochemical water splitting

目前的项目旨在通过光电化学水分解太阳能驱动的氢气形成，采用专门丰富的元素作为电极材料，为未来的氢气生产找到生态和经济上可行的解决方案。这就需要优化出氢和出氧反应的单个光吸收材料的形态和电荷收集效率。特别是，该项目旨在(i)利用模板辅助电化学沉积技术开发具有增强光响应的铁氧体MxFe3-xO4 （M =例如Zn， Mg, Ca）基光电极，（ii）深入了解铁氧体基光电化学电池中载流子和反应中间体的起源和动力学。(3)了解水和氢氧根离子在铁氧体不同晶面上的吸附以及掺杂和金属取代对其带隙和带位的影响。纳米结构的铁氧体电极将通过模板辅助电化学沉积和丝网印刷，由不同的复合、离子液体和微波辅助溶胶-凝胶途径获得的纳米粉末形成。本研究中使用的模板是具有芳香羧酸功能的小有机分子，在氧化物半导体沉积过程中，由于在某些晶体平面上的优先吸附导致不对称晶体生长，从而赋予孔隙度和/或特定的晶体取向。所获得的孔隙率和薄膜的晶体取向将决定电极的光效。激光闪光光解将成为探索和阐明反应中间体命运和电荷输运的有力工具。在这方面的信息，有关的寿命载流子，中间体，以及他们在水分解反应中的作用，将获得粉末和电极样品。基于它们的能量学，形貌和化学计量学优化的铁氧体将用于光催化z -方案和光电化学电池，这些电池将专门用于经济高效的水分解和在分离腔中形成纯氢。这个项目的一个组成部分是用系统的理论方法获得对相关过程的原子尺度的理解。利用第一性原理方法，我们将阐述铁氧体电极不同表面平面上固液界面与水和OH的表面相互作用机理。利用杂化DFT结合GW-BSE方法，研究了三元相和四相的吸附和MxNyFe3-x-yO4的组成对电子性能（带隙和带向）和表面结构的影响。

The current project aims on solar-driven hydrogen formation by photoelectrochemical water splitting employing exclusively abundant elements as electrode materials to find ecologically and economically feasible solutions for future hydrogen production. This requires the optimization of the morphology and the charge collection efficiency of the individual photo-absorber materials for hydrogen and oxygen evolution reactions. In particular, the project aims at (i) the development of ferrite, MxFe3-xO4 (M = e.g., Zn, Mg, Ca), based photoelectrodes with enhanced photoresponse utilizing template assisted electrochemical deposition, (ii) an in depth understanding of the origin and dynamics of charge carriers and reaction intermediates in ferrite based photoelectrochemical cells, and (iii) the understanding how water and hydroxide ion adsorption on the different crystallographic planes of the ferrites as well as doping and metal substitution affect their band gaps and band positions. Nanostructured ferrite based electrodes will be formed in template-assisted electrochemical deposition and via screen-printing from nanopowders obtained by different complex-, ionic liquid- and microwave-assisted sol-gel routes. The templates used in this study are small organic molecules with aromatic carboxylic acid functionality imparting porosity and/or specific crystallographic orientation during the deposition of oxide semiconductors due to preferential adsorption at certain crystal planes inducing asymmetric crystal growth. The obtained porosity and crystallographic orientation of the films will govern the photoefficiency of the electrodes. Laser flash photolysis will be used as a powerful tool to probe and elucidate the fate of reaction intermediates and charge transport. In this regard information relating to the lifetime of the charge carriers, the intermediate involved as well as their role in the water splitting reaction will be obtained for both powder and electrode samples. Based on their energetics the morphology and stoichiometry optimized ferrites will be used for photocatalytic Z-schemes and photoelectrochemical cells which will be specially designed for cost-effective water splitting and formation of pure hydrogen in a separated chamber. An integral part of this project is to gain atomic-scale understanding of the relevant processes using a systematic theoretical approach. By using first-principles methods we will elaborate the mechanisms of the surface interaction with water and OH from the solid-liquid interface on the various surface planes of ferrite electrodes. The effect of adsorption and MxNyFe3-x-yO4 composition of ternary and quaternary phases on the electronic properties (band gap and band alignment) and the surface structure will be obtained employing hybrid DFT in combination with a GW-BSE approach.