Abstract Water dissociation is an indispensable step in industrial as well as in natural processes. It is the rate-determining step in the industrially important water gas shift reaction. The barrier for the dissociation of H2O on metal surfaces is very high and therefore, the probabilities of H2O dissociation on these metal surfaces in the energy range of industrial relevance are very low. Thereby, there is a clear need of a better catalyst for this reaction. Bimetallic alloys have unique electronic and catalytic properties as compared to the respective monometals. In this present study, we have investigated the catalytic role played by the Ag/Ni bimetallic alloy surfaces towards H2O dissociation. This is a thermodynamically stable alloy and has already been synthesized experimentally as nanoparticles [J. Phys. Chem. C. 113 (2009) 1155–1159], [J. Phys. Chem. C. 114 (2010) 14,309–14,318] and this can aid the surface phenomenon. Systematic density functional theory calculations were performed on a series of overlayer starting from pure Ag(111) and we report the Ag-based catalyst, Ni9_Ag(111) (full monolayer coverage of Ni on Ag top layer) to act as a better catalyst with a barrier for H2O dissociation of 0.13 eV compared to 1.78 eV for pure Ag(111). A detailed analysis behind this lowering of the barrier is found to be governed by the large shift in the d-band center value of the metal due to alloying. Molecular orbital pictures provided further insight into the interactions of H2O with the surfaces. Transition state calculations also showed that the subsequent addition of Ni atom to Ag(111) surfaces decreases the dissociation barriers gradually. Finally, the semi-classical tunneling probability is computed using minimum energy path including the effect of surface temperature with the lattice atom motion. We observed an increase in surface temperature increases the dissociation probability, where, the extent of increase is strongly dependent on the change in the barrier heights.

中文翻译：

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Ag/Ni双金属合金表面水离解的多重增强

摘要 水离解是工业和自然过程中必不可少的步骤。它是工业上重要的水煤气变换反应中的速率决定步骤。H2O 在金属表面解离的障碍非常高，因此，在工业相关的能量范围内，H2O 在这些金属表面解离的概率非常低。因此，对于该反应显然需要更好的催化剂。与各自的单金属相比，双金属合金具有独特的电子和催化性能。在本研究中，我们研究了 Ag/Ni 双金属合金表面对 H2O 离解所起的催化作用。这是一种热力学稳定的合金，已经通过实验合成为纳米颗粒 [J. 物理。化学 C. 113 (2009) 1155–1159]，[J. 物理。化学 C. 114 (2010) 14,309–14,318] 这有助于表面现象。从纯 Ag(111) 开始对一系列覆盖层进行系统密度泛函理论计算，我们报告了基于 Ag 的催化剂 Ni9_Ag(111)（Ni 在 Ag 顶层的完全单层覆盖）作为更好的催化剂与纯 Ag(111) 的 1.78 eV 相比，H2O 解离势垒为 0.13 eV。发现这种势垒降低背后的详细分析是由合金化引起的金属 d 带中心值的大偏移所控制的。分子轨道图片提供了对 H2O 与表面相互作用的进一步了解。过渡态计算还表明，随后将 Ni 原子添加到 Ag(111) 表面会逐渐降低解离势垒。最后，半经典隧穿概率是使用最小能量路径计算的，包括表面温度与晶格原子运动的影响。我们观察到表面温度的增加会增加解离概率，其中增加的程度很大程度上取决于势垒高度的变化。