东北师范大学张昕彤教授ASS:通过Co-MOF衍生的异质结构的共催化促进BiVO4光阳极的光电化学水氧化过程

第一作者：Dan Wang

通讯作者：张昕彤 教授

通讯单位：东北师范大学

DOI:10.1016/j.apsusc.2023.156710

迟缓的表面反应动力学是限制BiVO4光电化学（PEC）水氧化的瓶颈，特别是对于具有高表面积的多孔结构的BiVO4。这里，Co基金属有机框架（MOFs）被修饰在多孔的BiVO4光阳极上，然后在N2气氛中进行煅烧，形成BiVO4-MOF-N2光阳极。由MOF衍生的异质结构助催化剂明显提高了BiVO4-MOF-N2的光电流密度，达到2.32 mA-cm-2（1.23 V vs RHE），约为BiVO4-MOF的1.15倍和原始BiVO4的2.64倍。对BiVO4-MOF-N2、BiVO4-MOF和原始BiVO4光阳极的比较研究表明，Co-MOF衍生的异质结构助催化剂在促进表面反应方面的作用比纯MOF强得多。与BiVO4和BiVO4-MOF相比，BiVO4-MOF-N2光阳极在1.3V vs RHE时具有最高的电荷转移效率，即63.1%，而且电荷转移电阻率最低。协同活性中心和导电碳基质都有助于增强BiVO4-MOF-N2光阳极的电荷转移。BiVO4光阳极的MOF-加载时间相关的PEC性能也表明，从BiVO4到活性中心的中间电荷转移过程强烈影响了最终的电荷转移和PEC性能。这项工作为设计基于异质结构cocatalysts的高性能光电化学电极提供了新的见解。

在本文中，我们提出了一项比较研究，以评估MOF衍生的异质结构助催化剂对BiVO4光阳极的PEC性能的影响。通过在室温下将原始BiVO4电极浸入MOF前体溶液中，在多孔BiVO4表面原位修饰不同负载时间的Co基MOFs（ZIF-67）。得到的BiVO4-MOF光阳极在氮气（N2）环境中退火，将MOF转化为具有Co-active反应中心的碳基。Co-MOF衍生的OECs明显增强了BiVO4光阳极的PEC性能。光电流密度达到2.32 mA-cm-2（1.23 V vs RHE），是BiVO4光阳极0.88 mA-cm-2的2.64倍，并且起始电位负向移动了200 mV。与纯粹的MOF催化剂相比，由于碳基体在BiVO4到Co-active中心的电荷转移过程中具有良好的导电性，因此MOF衍生的催化剂显示出更高的电荷转移效率和更低的电荷转移电阻率。这项工作可能对通过平衡表面活性点数量和电荷转移能力来促进光阳极表面的电荷转移过程提出了新的见解。

Fig. 1. The SEM images of (a) as-prepared porous BiVO4 photoelectrode, (b) BiVO4 immersed in MOF precursor solution for 30 min (BiVO4-MOF), and (c) BiVO4 immersed in MOF solution for 30 min followed by annealing in N2 gas (BiVO4-MOF-N2). SEM images with higher magnification of (d) BiVO4, (e) BiVO4-MOF, and (f) BiVO4-MOF-N2 photoelectrodes.Fig. 2. Bi, V, O, Co, C, and N elemental mapping of BiVO4-MOF-N2 photoelectrode.Fig. 3. (a) XRD patterns, (b) Raman spectra, and (c) light absorption spectra of pristine BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 photoelectrodes. (d) Light absorption spectra of Co-MOF powder and that after annealing in the N2 atmosphere (Co-MOF-N2).Fig. 4. (a), (b), and (c) are TEM images of BiVO4-MOF with different magnifications. (d), (e), and (f) are TEM images of BiVO4-MOF-N2 electrodes with different magnifications; (g) and (h) are enlarged HRTEM images in Fig. 4 (f).Fig. 5. XPS spectra of (a) Bi, (b) V, and (c) O elements in BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes.Fig. 6. XPS spectra of (a) C, (b) N, and (c) Co elements in BiVO4-MOF, and BiVO4-MOF-N2 electrodes.Fig. 7. (a) I-V curves of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes under the illumination of AM 1.5G with the scan rate of 10 mV·s−1; (b) The current density at 1.23 V vs RHE and onset potential of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes; (c) Photocurrent vs time curves measured under chopped light illumination at a time interval of 10 s; (d) The ratio of Ispike-steady and Isteady for electrodes of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes.Fig. 8. (a) The I-V curves of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes measured in the electrolyte of 0.5 M Na2SO4 with and without 0.1 M Na2SO3 as the hole scavenger. (b) The surface charge transfer efficiencies of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes. (c) Impedance spectra of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes. The inset in Fig. 8c is the equivalent circuit. (d) The fitted charge transfer resistivities of BiVO4, BiVO4-MOF, and BiVO4-MOF-N2 electrodes.Fig. 9. The Kelvin probe test of Au, BiVO4, MOF and MOF-N2 samples. (b) The calculated work function of BiVO4, MOF, and MOF-N2 samples. The schematic illustration of the energy band for BiVO4 and MOF-N2 (c) at equilibrium after contact, and (d) under the illumination.Fig. 10. (a) The I-V curves of BiVO4, BiVO4-N2, and BiVO4-MOF-N2 photoanodes with different deposition time in MOF precursor solution measured under irradiation of AM 1.5G simulated solar light. (b) Histogram of current densities of different samples at 1.23 V vs RHE. (c) The enlarged I-V curves in Fig. 10 (a). (d) Histogram of onset potential of different samples at 1.23 V vs RHE.

通过电沉积结合热退火方法制备了具有多孔结构的BiVO4光阳极。在室温下，通过原位反应在BiVO4的表面修饰了MOF。在N2环境下退火后，MOF衍生的助催化剂被装饰在BiVO4光阳极上。比较研究表明，与BiVO4-MOF和原始BiVO4光阳极相比，BiVO4-MOF-N2具有最强的水氧化性能。BiVO4-MOF-N2的光电流密度达到2.32 mA-cm-2（1.23 V vs RHE），是BiVO4-MOF光阳极的1.15倍，是原始BiVO4的2.64倍。BiVO4-MOF-N2电极在1.3V vs RHE时具有最高的电荷转移效率，为63.1%，约为BiVO4和BiVO4-MOF的1.7和1.2倍，同时电荷转移电阻率最低。协同活性中心和导电碳基体都有助于提高BiVO4-MOF-N2光阳极的电荷传输能力。研究还发现，MOF的适当负载对于平衡活性表面位点和电荷转移能力以优化BiVO4光阳极的PEC行为非常重要。这项工作为开发MOF衍生的高性能光阳极用的助催化剂提供了新的见解。

Dan Wang, Jiangli Gu, Hanlin Wang, Mingzhuang Liu, Yichun Liu, Xintong Zhang, Promoting photoelectrochemical water oxidation of BiVO4 photoanode via Co-MOF-derived heterostructural cocatalyst, Applied Surface Science, 2023, https://doi.org/10.1016/j.apsusc.2023.156710

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