Department of Physics, CINF, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
J Am Chem Soc. 2013 Jan 23;135(3):1057-64. doi: 10.1021/ja309523t. Epub 2013 Jan 11.
Surface passivation is a general issue for Si-based photoelectrodes because it progressively hinders electron conduction at the semiconductor/electrolyte interface. In this work, we show that a sputtered 100 nm TiO(2) layer on top of a thin Ti metal layer may be used to protect an n(+)p Si photocathode during photocatalytic H(2) evolution. Although TiO(2) is a semiconductor, we show that it behaves like a metallic conductor would under photocathodic H(2) evolution conditions. This behavior is due to the fortunate alignment of the TiO(2) conduction band with respect to the hydrogen evolution potential, which allows it to conduct electrons from the Si while simultaneously protecting the Si from surface passivation. By using a Pt catalyst the electrode achieves an H(2) evolution onset of 520 mV vs NHE and a Tafel slope of 30 mV when illuminated by the red part (λ > 635 nm) of the AM 1.5 spectrum. The saturation photocurrent (H(2) evolution) was also significantly enhanced by the antireflective properties of the TiO(2) layer. It was shown that with proper annealing conditions these electrodes could run 72 h without significant degradation. An Fe(2+)/Fe(3+) redox couple was used to help elucidate details of the band diagram.
表面钝化是硅基光电电极的一个普遍问题，因为它会逐渐阻碍半导体/电解质界面处的电子传导。在这项工作中，我们表明，在薄钛金属层顶部溅射的 100nm TiO2 层可用于在光催化 H2 演化过程中保护 n+ p Si 光电阴极。尽管 TiO2 是一种半导体，但我们表明，在光阴极 H2 演化条件下，它的行为类似于金属导体。这种行为是由于 TiO2 导带与析氢电位的幸运对准，这允许它从 Si 传导电子，同时保护 Si 免受表面钝化的影响。通过使用 Pt 催化剂，电极在 AM 1.5 光谱的红光部分（λ > 635nm）照射下实现了 520mV 对 NHE 的 H2 演化起始电位和 30mV 的塔菲尔斜率。TiO2 层的抗反射特性也显著增强了饱和光电流（H2 演化）。结果表明，在适当的退火条件下，这些电极可以连续运行 72 小时而没有明显的降解。Fe(2+)/Fe(3+)氧化还原偶联物用于帮助阐明能带图的细节。
