Lei Lei, Sang Lixia, Zhang Yudong, Gao Yunlong
Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Key Laboratory of Heat Transfer and Energy Conversion, Beijing Municipality, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China.
ACS Omega. 2020 Feb 11;5(7):3522-3532. doi: 10.1021/acsomega.9b03847. eCollection 2020 Feb 25.
Hydrogen can be produced by photoelectrochemical (PEC) water splitting using a KOH solution as an electrolyte and TiO as a photoanode. In this work, we fabricated anatase TiO nanoring/nanotube arrays and TiO nanotube arrays using an anodic oxidation method, confirmed by field-emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD), and then conducted the photoelectrochemical experiments with 1 M KOH and NaSO solutions. The bias voltage, small impedance, negative flat-band potential, large capacitance, and depletion layer width in the anatase TiO-KOH system were observed, leading to the stable and large photocurrent density. To understand the effects of KOH on the interface properties of TiO/HO, the electric double layers of anatase TiO(001), (100), (101)/KOH interfaces were further investigated by calculating the ion-surface interaction with molecular dynamics simulations. It is noted that the number density of potassium ions has the same trend as that of oxygen atoms due to the layering effect in liquids and the strongest ionic hydration of K on anatase (101) is observed by analyzing the radial distribution function and coordination number. In addition, the electrostatic characteristics along the TiO/KOH interfaces were analyzed based on the Grahame double layer model. The potential drops in the outer Helmholtz layer of anatase (001), (100), and (101) surfaces are 1.08, 0.26, and 0.51 V, respectively. Compared with TiO-HO systems, the larger potential drops in the TiO-KOH system explain the phenomenon that KOH solute contributes substantially to a chemical bias in PEC reactions. At the same time, we estimated the depletion layer widths of anatase TiO(001), (100), and (101) surfaces as 37.48, 173.25, and 64.49 Å, respectively, which are of similar magnitude to the experimental results. Anatase TiO(100) with the widest depletion layer is suggested in photocatalysis. These works provide a clear understanding of interfacial behavior of KOH on anatase TiO from a microscale, which can be used to explain the promotion effect of the KOH electrolyte and guide the design of TiO nanocrystals in the PEC system.
氢气可以通过光电化学（PEC）水分解产生，使用氢氧化钾（KOH）溶液作为电解质，二氧化钛（TiO）作为光阳极。在这项工作中，我们采用阳极氧化法制备了锐钛矿型TiO纳米环/纳米管阵列和TiO纳米管阵列，通过场发射扫描电子显微镜（FESEM）和X射线衍射仪（XRD）进行了确认，然后在1 M KOH和NaSO溶液中进行了光电化学实验。观察到锐钛矿型TiO-KOH体系中的偏置电压、小阻抗、负平带电位、大电容和耗尽层宽度，从而产生稳定且大的光电流密度。为了理解KOH对TiO/H₂O界面性质的影响，通过分子动力学模拟计算离子与表面的相互作用，进一步研究了锐钛矿型TiO(001)、(100)、(101)/KOH界面的双电层。值得注意的是，由于液体中的分层效应，钾离子的数密度与氧原子的数密度具有相同的趋势，并且通过分析径向分布函数和配位数，观察到K在锐钛矿(101)上具有最强的离子水合作用。此外，基于格雷厄姆双层模型分析了沿TiO/KOH界面的静电特性。锐钛矿(001)、(100)和(101)表面在亥姆霍兹外层的电位降分别为1.08、0.26和0.51 V。与TiO-H₂O体系相比，TiO-KOH体系中较大的电位降解释了KOH溶质对PEC反应中的化学偏置有显著贡献的现象。同时，我们估计锐钛矿型TiO(001)、(100)和(101)表面的耗尽层宽度分别为37.48、173.25和64.49 Å，这与实验结果的量级相似。在光催化中建议使用耗尽层最宽的锐钛矿型TiO(100)。这些工作从微观尺度上清楚地理解了KOH在锐钛矿型TiO上的界面行为，这可用于解释KOH电解质的促进作用，并指导PEC系统中TiO纳米晶体的设计。
