Institut Universitari d'Electroquímica i Departament de Química Física, Universitat d'Alacant, Apartat 99, E-03080 Alacant, Spain.
Chemphyschem. 2012 Aug 27;13(12):3008-17. doi: 10.1002/cphc.201200072. Epub 2012 Jun 27.
The presence of electronic traps in nanoporous TiO(2) electrodes has been studied by cyclic voltammetry in aqueous media. These simple measurements allow us to map the density of states, providing evidence for the presence of a relatively small number of discrete electron traps at the band gap. We have taken advantage of the variety of TiO(2) synthetic procedures that lead to well-defined morphologies (such as nanowires, nanocolumns, nanotubes, and nanoparticles) of anatase and rutile to investigate the nature of these electron traps. They derive from the structural disorder at the contact between neighboring crystalline nanoparticles. As expected, both their density and energetic location are highly dependent, not only on the crystalline structure (whether it is anatase or rutile), but also on the electrode morphology (i.e. the facets that meet at the grain boundaries). The trap density is also sensitive to pH changes and to the presence of some adsorbates. This variation of the number of traps with the electrolyte indicates that on one hand, an apparent electronic density of states is actually measured. On the other, it indicates that the traps are surface-related in agreement with their particular location at the perimeter of the grain boundaries. The effect of these traps on the observed electrode catalytic reactivity has also been studied. In the dark, it is found that they are directly involved in the electron transfer toward oxygen. In addition, under illumination, the trap states show a deleterious effect, favoring electron recombination.
通过在水溶液中的循环伏安法研究了纳米多孔 TiO(2) 电极中电子陷阱的存在。这些简单的测量允许我们绘制态密度图，为带隙中存在相对少量离散电子陷阱提供了证据。我们利用导致具有明确形态（如纳米线、纳米柱、纳米管和纳米颗粒）的锐钛矿和金红石 TiO(2) 合成程序的多样性来研究这些电子陷阱的性质。它们源于相邻结晶纳米颗粒之间的结构无序。正如预期的那样，它们的密度和能量位置不仅高度依赖于结晶结构（是锐钛矿还是金红石），而且还依赖于电极形态（即晶粒边界处相遇的晶面）。陷阱密度也对 pH 值变化和某些吸附物的存在敏感。这种随电解质的陷阱数量的变化表明，一方面，实际上测量了明显的电子态密度。另一方面，这表明陷阱与表面有关，与它们在晶粒边界周长的特殊位置一致。还研究了这些陷阱对观察到的电极催化活性的影响。在黑暗中，发现它们直接参与向氧的电子转移。此外，在光照下，陷阱态表现出有害影响，有利于电子复合。
