Bismuth vanadate (BiVO₄) has emerged as one of the most promising photoanode materials for oxidising water due to its visible light activity and low cost. Recent studies have shown that the performance of BiVO₄ photoanodes can be remarkably improved when coated with ultra-thin passivation layers. In this article we investigate the use of ultra-thin Al₂O₃ layers grown using atomic layer deposition (ALD). At an optimum thickness (∼0.33 nm, 3 ALD cycles), the Al₂O₃ layer favourably shifted the onset potential by ∼200 mV and increased photocatalytic currents for the water oxidation reaction. When held at 1.23 V_RHE, we observe a remarkable increase in the theoretical solar photocurrent; from ∼0.47 mAcm⁻² in uncoated BiVO₄ to ∼3.0 mAcm⁻² in Al₂O₃-coated BiVO₄. Using transient photocurrent (TPC) and transient absorption spectroscopy (TAS) the charge carrier dynamics in Al₂O₃-coated BiVO₄ photoanodes were examined for the first time. TPC showed that photogenerated electrons in the BiVO₄ layer were extracted within ∼1 ms. TAS showed that the remaining holes oxidised water from ∼100 ms to 1 s. Ultra-thin Al₂O₃ coatings did not improve the reaction kinetics towards water oxidation, but rather, suppressed bi-molecular recombination on the μs-ms timescale in BiVO₄, and increased the yield of long-lived holes on the ms-s timescale required to oxidise water. This is attributed to an inhibition of surface recombination on BiVO₄ by Al₂O₃, which inhibited the early timescale recombination of charge carriers formed within the space charge layer.

钒酸铋（BiVO ₄）由于其可见光活性和低成本而成为最有希望的用于氧化水的光阳极材料之一。最近的研究表明，当涂有超薄钝化层时，BiVO ₄光电阳极的性能可以得到显着改善。在本文中，我们研究了使用原子层沉积（ALD）生长的超薄Al ₂ O ₃层的使用。在最佳厚度（约0.33 nm，3个ALD循环）下，Al ₂ O ₃层可将起始电势良好地偏移约200 mV，并增加了水氧化反应的光催化电流。保持在1.23 V _RHE时，我们发现理论太阳光电流显着增加；从~0.47 MACM ^-2在未涂覆的BiVO ₄至〜3.0 MACM ^-2以Al ₂ ö ₃涂覆的BiVO ₄。使用瞬态光电流（TPC）和瞬态吸收光谱（TAS），首次检测了Al ₂ O ₃涂层的BiVO _4光阳极中的载流子动力学。TPC显示BiVO ₄层中的光生电子在约1毫秒内被提取。TAS显示，剩余的孔在约100 ms到1 s的时间内将水氧化。超薄Al ₂ O ₃涂层没有改善水氧化的反应动力学，而是在BiVO _4中以μs-ms的时间尺度抑制了双分子重组，并以ms-s的时间尺度增加了氧化水所需的长寿命空穴的产率。这归因于Al ₂ O ₃抑制BiVO ₄上的表面重组，从而抑制了在空间电荷层内形成的载流子的早期时标重组。