Pethica Brian A
Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA.
Phys Chem Chem Phys. 2007 Dec 21;9(47):6253-62. doi: 10.1039/b706153f. Epub 2007 Oct 16.
As indicated by Gibbs and made explicit by Guggenheim, the electrical potential difference between two regions of different chemical composition cannot be measured. The Gibbs-Guggenheim Principle restricts the use of classical electrostatics in electrochemical theories as thermodynamically unsound with some few approximate exceptions, notably for dilute electrolyte solutions and concomitant low potentials where the linear limit for the exponential of the relevant Boltzmann distribution applies. The Principle invalidates the widespread use of forms of the Poisson-Boltzmann equation which do not include the non-electrostatic components of the chemical potentials of the ions. From a thermodynamic analysis of the parallel plate electrical condenser, employing only measurable electrical quantities and taking into account the chemical potentials of the components of the dielectric and their adsorption at the surfaces of the condenser plates, an experimental procedure to provide exceptions to the Principle has been proposed. This procedure is now reconsidered and rejected. No other related experimental procedures circumvent the Principle. Widely-used theoretical descriptions of electrolyte solutions, charged surfaces and colloid dispersions which neglect the Principle are briefly discussed. MD methods avoid the limitations of the Poisson-Bolzmann equation. Theoretical models which include the non-electrostatic components of the inter-ion and ion-surface interactions in solutions and colloid systems assume the additivity of dispersion and electrostatic forces. An experimental procedure to test this assumption is identified from the thermodynamics of condensers at microscopic plate separations. The available experimental data from Kelvin probe studies are preliminary, but tend against additivity. A corollary to the Gibbs-Guggenheim Principle is enunciated, and the Principle is restated that for any charged species, neither the difference in electrostatic potential nor the sum of the differences in the non-electrostatic components of the thermodynamic potential difference between regions of different chemical compositions can be measured.
如吉布斯所指出并由古根海姆明确说明的那样，两个化学成分不同的区域之间的电势差无法测量。吉布斯 - 古根海姆原理限制了经典静电学在电化学理论中的应用，因为从热力学角度来看这是不合理的，只有少数近似的例外情况，特别是对于稀电解质溶液以及伴随的低电势，此时相关玻尔兹曼分布指数的线性极限适用。该原理使广泛使用的不包括离子化学势非静电成分的泊松 - 玻尔兹曼方程形式无效。通过对平行板电容器进行热力学分析，仅使用可测量的电学量，并考虑电介质成分的化学势及其在电容器极板表面的吸附情况，提出了一种为该原理提供例外情况的实验程序。现在重新考虑并否定了这个程序。没有其他相关实验程序能规避该原理。简要讨论了忽视该原理的电解质溶液、带电表面和胶体分散体系的广泛使用的理论描述。分子动力学方法避免了泊松 - 玻尔兹曼方程的局限性。在溶液和胶体系统中包含离子间和离子 - 表面相互作用非静电成分的理论模型假定色散力和静电力具有可加性。从微观极板间距下电容器的热力学中确定了一个测试该假设的实验程序。开尔文探针研究的现有实验数据是初步的，但倾向于否定可加性。阐述了吉布斯 - 古根海姆原理的一个推论，并重新表述该原理，即对于任何带电物种，不同化学成分区域之间的静电势差以及热力学势差的非静电成分差之和均无法测量。
