Department of Chemistry and ‡Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
ACS Nano. 2014 Dec 23;8(12):12199-207. doi: 10.1021/nn503869n. Epub 2014 Dec 3.
Hematite (α-Fe2O3) is one of just a few candidate electrode materials that possess all of the following photocatalyst-essential properties for scalable application to water oxidation: excellent stability, earth-abundance, suitability positive valence-band-edge energy, and significant visible light absorptivity. Despite these merits, hematite's modest oxygen evolution reaction kinetics and its poor efficiency in delivering photogenerated holes, especially holes generated by green photons, to the electrode/solution interface, render it ineffective as a practical water-splitting catalyst. Here we show that hole delivery and catalytic utilization can be substantially improved through Ti alloying, provided that the alloyed material is present in ultrathin-thin-film form. Notably, the effects are most pronounced for charges photogenerated by photons with energy comparable to the band gap for excitation of Fe(3d)→Fe(3d) transitions (i.e., green photons). Additionally, at the optimum Ti substitution level the lifetimes of surface-localized holes, competent for water oxidation, are extended. Together these changes explain an overall improvement in photoelectrochemical performance, especially enhanced internal quantum efficiencies, observed upon Ti(IV) incorporation.
赤铁矿 (α-Fe2O3) 是少数几种候选电极材料之一，它具有以下可扩展应用于水氧化的光催化剂基本特性：极好的稳定性、丰富的地球资源、适合的正价带边缘能量和显著的可见光吸收能力。尽管有这些优点，但赤铁矿的氧析出反应动力学性能中等，其在将光生空穴，特别是绿光产生的空穴，输送到电极/溶液界面的效率较差，使得它无法作为一种实用的水分解催化剂。在这里，我们表明通过钛合金化可以大大提高空穴的传递和催化利用效率，前提是合金材料以超薄薄膜的形式存在。值得注意的是，对于能量与激发 Fe(3d)→Fe(3d)跃迁的能带间隙相当的光子（即绿光）产生的电荷，这些效果最为明显。此外，在最佳 Ti 取代水平下，表面局域空穴的寿命，即胜任水氧化的空穴寿命，得以延长。这些变化共同解释了光电化学性能的整体提高，特别是在 Ti(IV)掺入后观察到的内量子效率的提高。
