Zhu Xiaodi, Guijarro Néstor, Liu Yongpeng, Schouwink Pascal, Wells Rebekah A, Le Formal Florian, Sun Song, Gao Chen, Sivula Kevin
Laboratory for Molecular Engineering of Optoelectronic Nanomaterials (LIMNO), École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015, Lausanne, Switzerland.
National Synchrotron Radiation Laboratory, University of Science and Technology of China, No.42, Hezuohua Road, Hefei, Anhui, 230029, P. R. China.
Adv Mater. 2018 Jul 5:e1801612. doi: 10.1002/adma.201801612.
Zinc spinel ferrite, ZnFe O (ZFO), is an emerging photoanode material for photoelectrochemical (PEC) solar fuel production. However, a lack of fundamental insight into the factors limiting the photocurrent has prevented substantial advance in its performance. Herein, it is found that ZFO nanorod array photoelectrodes with varying crystallinity exhibit vastly different PEC properties. Using a sacrificial hole scavenger (H O ), spatially defined carrier generation, and electrochemical impedance spectroscopy, it is shown that ZFO with a relatively poor crystallinity but a higher spinel inversion degree (due to cation disorder) exhibits superior photogenerated charge separation efficiency and improved majority charge carrier transport compared to ZFO with higher crystallinity and a lower inversion degree. Conversely, the latter condition leads to better charge injection efficiency. Optimization of these factors, and the addition of a nickel-iron oxide cocatalyst overlayer, leads to a new benchmark solar photocurrent for ZFO of 1.0 mA cm at 1.23 V versus reversible hydrogen electrode (RHE) and 1.7 mA cm at 1.6 V versus RHE. Importantly, the observed correlation between the cation disorder and the PEC performance represents a new insight into the factors important to the PEC performance of the spinel ferrites and suggests a path to further improvement.
锌铁氧体尖晶石（ZnFe₂O₄，ZFO）是一种新兴的用于光电化学（PEC）太阳能燃料生产的光阳极材料。然而，由于缺乏对限制光电流因素的基本认识，其性能一直未能取得实质性进展。在此，研究发现具有不同结晶度的ZFO纳米棒阵列光电极表现出截然不同的PEC性能。通过使用牺牲空穴清除剂（H₂O₂）、空间定义的载流子产生以及电化学阻抗谱，研究表明，与结晶度较高且反演程度较低的ZFO相比，结晶度相对较差但尖晶石反演程度较高（由于阳离子无序）的ZFO表现出卓越的光生电荷分离效率以及改善的多数电荷载流子传输。相反，后一种情况导致更好的电荷注入效率。对这些因素进行优化，并添加镍铁氧化物助催化剂覆盖层，使得ZFO在相对于可逆氢电极（RHE）为1.23 V时产生了1.0 mA cm⁻²的新基准太阳能光电流，在相对于RHE为1.6 V时产生了1.7 mA cm⁻²的光电流。重要的是，观察到的阳离子无序与PEC性能之间的相关性代表了对影响尖晶石铁氧体PEC性能的重要因素的新认识，并为进一步改进指明了方向。
