用于光电化学器件与制氢的 Sr$_{1-x}$Ca$_x$TaO$_2$N / H$_2$O 界面能带对齐研究
Band alignment study of the Sr$_{1-x}$Ca$_x$TaO$_2$N / H$_2$O interface for photoelectrochemical devices and Hydrogen production
AI总结：
本文通过第一性原理计算研究 Sr$_{1-x}$Ca$_x$O$_2$N 与水界面的能带对齐，验证其适用于无偏压光电化学制氢，并揭示 Ca 部分取代 Sr 可调控带隙和对齐以提升性能。
摘要：
氢是最有前景的清洁能源生产候选之一。光电化学器件在将水分子分解为 2H$_2$ + O$_2$ 方面显示出良好前景。氧氮化物，例如固溶体 Sr$_{1-x}$Ca$_x$O$_2$N，由于带隙较小且位于太阳辐射光谱的最大区域，因此是良好的候选材料。光电化学过程在无偏压下工作的必要条件是：半导体导带最小值必须比 H$^+$ 还原为 H$_2$ 的还原电位更正，而半导体价带最大值必须比 H$_2$O 氧化为 O$_2$ 的氧化电位更负。因此，半导体与水界面的能带对齐研究变得非常重要。这些研究存在若干微妙之处，因为不同或过于简化的建模会导致十分之几电子伏特的差异，从而产生错误的能带对齐预测。因此，寻找一种可靠的方法是值得期待的。本工作基于密度泛函理论（DFT）的第一性原理计算，采用全电子方法和赝势方法，对 Sr$_{1-x}$Ca$_x$O$_2$N /H$_2$O 界面的能带对齐进行了分析。对表面、超胞以及与水分子的界面建模进行了详细研究。实验数据用于结构和光电化学行为，并被所实现的方法很好地再现。所进行的分析得到了与实验结果一致的理论结果：计算表明 Sr$_{1-x}$Ca$_x$O$_2$N /H$_2$O 适用于光电化学应用，并且用 Ca 部分取代 Sr 可以实现带隙和能带对齐的调控，从而增强整体性能。
英文摘要：
Hydrogen is one of the most promising candidates for clean energy production. Photoelectrochemical devices look promising for the decomposition of the water molecule into 2H$_2$ + O$_2$. Oxynitrides, like the solid solution Sr$_{1-x}$Ca$_x$O$_2$N, are good candidates due to the low band gap that lies into the maximum zone of the solar radiation spectrum. A necessary condition for the photoelectrochemical process to work without a bias voltage is that the minimum of the semiconductor conduction band must be more positive than the reduction potential H$^+$ to H$_2$, whereas the maximum of the semiconductor valence band must be more negative than the oxidation potential of H$_2$O to O$_2$. Thus, band alignment studies in interfaces of semiconductors with water become of great importance. They present several subtleties, as different or simplistic modelling will result in few decimes of eV difference that would lead to a wrong prediction in the alignment. So, to find a trustful method is desirable. In this work, first principles calculations based on density functional theory (DFT) in the all electron and the pseudopotential approaches have been performed for the analysis of the band alignment in Sr$_{1-x}$Ca$_x$O$_2$N /H$_2$O interfaces. A detailed study of the modelling of the surface, supercells, and interface with water molecules was done. Experimental data were taken for the structures and photoelectrochemical behaviour and well reproduced by the methodology implemented. The analysis carried out led to theoretical results compatible with the experimental results: the calculations show that the Sr$_{1-x}$Ca$_x$O$_2$N /H$_2$O is suitable for photoelectrochemical applications, and the partial substitution of Sr by Ca enables the gap and alignment tuning thus enhancing the complex performance.
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