Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Solar Fuels , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
Department of Chemistry, University of Zurich , Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
J Am Chem Soc. 2017 Oct 25;139(42):15094-15103. doi: 10.1021/jacs.7b07847. Epub 2017 Oct 17.
A new strategy of using forward gradient self-doping to improve the charge separation efficiency in metal oxide photoelectrodes is proposed. Gradient self-doped CuBiO photocathodes are prepared with forward and reverse gradients in copper vacancies using a two-step, diffusion-assisted spray pyrolysis process. Decreasing the Cu/Bi ratio of the CuBiO photocathodes introduces Cu vacancies that increase the carrier (hole) concentration and lowers the Fermi level, as evidenced by a shift in the flat band toward more positive potentials. Thus, a gradient in Cu vacancies leads to an internal electric field within CuBiO, which can facilitate charge separation. Compared to homogeneous CuBiO photocathodes, CuBiO photocathodes with a forward gradient show highly improved charge separation efficiency and enhanced photoelectrochemical performance for reduction reactions, while CuBiO photocathodes with a reverse gradient show significantly reduced charge separation efficiency and photoelectrochemical performance. The CuBiO photocathodes with a forward gradient produce record AM 1.5 photocurrent densities for CuBiO up to -2.5 mA/cm at 0.6 V vs RHE with HO as an electron scavenger, and they show a charge separation efficiency of 34% for 550 nm light. The gradient self-doping accomplishes this without the introduction of external dopants, and therefore the tetragonal crystal structure and carrier mobility of CuBiO are maintained. Lastly, forward gradient self-doped CuBiO photocathodes are protected with a CdS/TiO heterojunction and coated with Pt as an electrocatalyst. These photocathodes demonstrate photocurrent densities on the order of -1.0 mA/cm at 0.0 V vs RHE and evolve hydrogen with a faradaic efficiency of ∼91%.
提出了一种利用前向梯度自掺杂提高金属氧化物光电极电荷分离效率的新策略。采用两步扩散辅助喷雾热解法,在铜空位中制备具有正向和反向梯度的梯度自掺杂 CuBiO 光阴极。降低 CuBiO 光阴极的 Cu/Bi 比会引入 Cu 空位,从而增加载流子(空穴)浓度并降低费米能级,这可以通过平带向更正的电位移动来证明。因此,Cu 空位的梯度导致 CuBiO 内产生内电场,这可以促进电荷分离。与均匀的 CuBiO 光阴极相比,具有正向梯度的 CuBiO 光阴极表现出高度改善的电荷分离效率和增强的还原反应光电化学性能,而具有反向梯度的 CuBiO 光阴极则表现出明显降低的电荷分离效率和光电化学性能。具有正向梯度的 CuBiO 光阴极在以 HO 作为电子捕获剂时,在 0.6 V vs RHE 下可产生高达 -2.5 mA/cm 的 AM 1.5 光电流密度,创下 CuBiO 的记录,并且在 550nm 光下的电荷分离效率为 34%。梯度自掺杂在不引入外部掺杂剂的情况下实现了这一点,因此 CuBiO 的四方晶体结构和载流子迁移率得以保持。最后,用 CdS/TiO 异质结保护正向梯度自掺杂 CuBiO 光阴极,并涂覆 Pt 作为电催化剂。这些光阴极在 0.0 V vs RHE 时的光电流密度约为 -1.0 mA/cm,并以约 91%的法拉第效率演化出氢气。