Controlling sub-microsecond desorption of water and other impurities from electrode surfaces at high heating rates is crucial for pulsed power applications. Despite the short time scales involved, quasi-equilibrium ideas based on transition state theory (TST) and Arrhenius temperature dependence have been widely applied to fit desorption barriers. In this work, we apply molecular dynamics (MD) simulations in conjunction with equilibrium potential-of-mean-force (PMF) techniques to directly compute the free energy barrier (Delta G*) associated with desorption of intact water molecules from Fe(2)O(3) and Cr(2)O(3) (0001) surfaces. The desorption free energy profiles are diffuse, without maxima, and have substantial dependences on temperature and surface water coverage. Incorporating the predicted Delta G* into an analytical form gives rate equations that are in reasonable agreement with non-equilibrium molecular dynamics desorption simulations. We also show that different Delta G* analytical functional forms which give similar predictions at a particular heating rate can yield desorption times that differ by up to a factor of four or more when the ramp rate is extrapolated by 8 orders of magnitude. This highlights the importance of constructing a physically-motivated Delta G* functional form to predict fast desorption kinetics.

中文翻译：

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快速加热金属氧化物表面水解吸动力学的准平衡预测


在高加热速率下控制水和其他杂质从电极表面的亚微秒解吸对于脉冲功率应用至关重要。尽管涉及的时间尺度很短，但基于过渡态理论（TST）和阿伦尼乌斯温度依赖性的准平衡思想已被广泛应用于拟合解吸势垒。在这项工作中，我们将分子动力学 (MD) 模拟与平衡平均力势 (PMF) 技术结合起来，直接计算与完整水分子从 Fe(2) 解吸相关的自由能垒 (Delta G*) )O(3) 和 Cr(2)O(3) (0001) 表面。解吸自由能分布是分散的，没有最大值，并且对温度和地表水覆盖有很大的依赖性。将预测的 Delta G* 纳入分析形式可得出与非平衡分子动力学解吸模拟合理一致的速率方程。我们还表明，当升温速率外推 8 个数量级时，在特定加热速率下给出类似预测的不同 Delta G* 分析函数形式可以产生高达四倍或更多差异的解吸时间。这凸显了构建物理驱动的 Delta G* 功能形式来预测快速解吸动力学的重要性。