Rettenmaier Karin, Berger Thomas
Department of Chemistry and Physics of Materials, University of Salzburg, Salzburg, Austria.
Front Chem. 2021 Nov 2;9:772116. doi: 10.3389/fchem.2021.772116. eCollection 2021.
Mesoporous films and electrodes were prepared from aqueous slurries of isolated anatase TiO nanoparticles. The resulting layers were annealed in air at temperatures 100°C ≤ ≤ 450°C upon preservation of internal surface area, crystallite size and particle size. The impact of processing temperature on charge separation efficiency in nanoparticle electrodes was tracked photocurrent measurements in the presence of methanol as a hole acceptor. Thermal annealing leads to an increase of the saturated photocurrent and thus of the charge separation efficiency at positive potentials. Furthermore, a shift of capacitive peaks in the cyclic voltammograms of the nanoparticle electrodes points to the modification of the energy of deep traps. Population of these traps triggers recombination possibly due to the action of local electrostatic fields attracting photogenerated holes. Consequently, photocurrents saturate at potentials, at which deep traps are mostly depopulated. Charge separation efficiency was furthermore investigated for nanoparticle films and was tracked via the decomposition of hydrogen peroxide. Our observations evidence an increase of charge separation efficiency upon thermal annealing. The effect of particle consolidation, which we associate with minute atomic rearrangements at particle/particle contacts, is attributed to the energetic modification of deep traps and corresponding modifications of charge transport and recombination, respectively.
介孔薄膜和电极由分离出的锐钛矿型TiO纳米颗粒的水性浆料制备而成。所得层在空气中于100°C≤≤450°C的温度下退火，同时保持内表面积、微晶尺寸和颗粒尺寸。在存在甲醇作为空穴受体的情况下，通过光电流测量追踪了加工温度对纳米颗粒电极中电荷分离效率的影响。热退火导致饱和光电流增加，从而在正电位下电荷分离效率提高。此外，纳米颗粒电极循环伏安图中电容峰的移动表明深陷阱能量发生了改变。这些陷阱的填充可能由于局部静电场吸引光生空穴的作用而引发复合。因此，光电流在深陷阱大多排空的电位下达到饱和。还对纳米颗粒薄膜的电荷分离效率进行了研究，并通过过氧化氢的分解进行追踪。我们的观察结果证明热退火后电荷分离效率提高。颗粒固结的影响，我们将其与颗粒/颗粒接触处的微小原子重排相关联，分别归因于深陷阱的能量改变以及电荷传输和复合的相应改变。
