Kramer Denis, Wang Yikun, Wharton Julian
Engineering Materials, Engineering Sciences, University of Southampton, Hants SO17 1BJ, UK.
Faraday Discuss. 2015;180:137-49. doi: 10.1039/c4fd00247d. Epub 2015 May 5.
In an attempt to elucidate the relationship and underlying processes of metal oxidation under stress, we combined the electrochemical characterisation with Density-Functional-Theory (DFT) calculations to interrogate the (100) surface of copper. The oxidised (100) surface shows a missing-row reconstruction, which is believed to be driven by surface stress. Hence, additional mechanical stimuli might have a significant impact on the onset of Cu oxidation. We find that different surface sites respond differently to strain. Oads at the thermodynamically favoured high-coordination hollow site (O coordinated to four Cu) is stabilised by up to 130 meV by imposing 2% tensile strain onto the surface, while the low-coordination top site (O coordinated to one Cu) shows a markedly different sensitivity. By cramping into the hollow site, Oads induces compressive stress into the (100) surface, an effect that is largely absent for the adsorption at the top site. We also find that the thermodynamic advantage of reconstructive underpotential surface oxidation is diminished under tensile strain. Hence, imposing tensile stress counter-balances the oxygen induced surface stress, which might have an implication on the onset of bulk copper oxidation. Studying Cu(100) single crystal surfaces in perchloric acid using cyclic voltammetry, we were able to confirm sensitivity of the electrochemical response towards the elastic strain.
为了阐明应力作用下金属氧化的关系及潜在过程，我们将电化学表征与密度泛函理论（DFT）计算相结合，以研究铜的(100)表面。氧化后的(100)表面呈现出缺行重构，据信这是由表面应力驱动的。因此，额外的机械刺激可能会对铜氧化的起始产生重大影响。我们发现不同的表面位点对应变的响应不同。通过在表面施加2%的拉伸应变，热力学上有利的高配位空心位点（一个氧原子与四个铜原子配位）上的吸附氧（Oads）稳定化高达130毫电子伏特，而低配位顶部位点（一个氧原子与一个铜原子配位）则表现出明显不同的敏感性。通过挤进空心位点，吸附氧会在(100)表面诱导压应力，而在顶部位点吸附时基本不存在这种效应。我们还发现，在拉伸应变下，重构欠电位表面氧化的热力学优势会减弱。因此，施加拉伸应力可抵消氧诱导的表面应力，这可能对块状铜氧化的起始有影响。我们使用循环伏安法研究了高氯酸中铜(100)单晶表面，从而能够证实电化学响应对应变的敏感性。
