Some Questionable Approaches in Interfacial Electrochemistry—The Charged State of Adsorbed Species and Their Involvement in Redox Processes

On the basis of a survey on the relevant literature it can be stated that some views and approaches concerning the charged state of adsorbed species and the charge transfer processes occurring with them are far from being unambiguous even in some respect they contradict fundamental physical and physicochemical principles. The meaning of the electrosorption valency, the misleading formulation of the Gibbs adsorption equation, and the interpretation of redox processes occurring with adsorbed species, is discussed in detail. It has been concluded that although the electrosorption valency of an adsorbed species as usually defined is an extra-thermodynamic and self-contradictory concept, experimental determined formal partial charge numbers can be a useful tool for scientists investigating adsorption phenomena, since the observed deviation between its value and the charge number of the same species in the solution phase unequivocally indicates a non-simple mechanism of the adsorption process, which should be taken into account in theoretical interpretation of the experimental data. It has been emphasized that the evaluation of voltammetric curves obtained in the presence of adsorbed redox partners requires a cautious analysis of the accompanying chemical transformations. In the framework of a critical analysis it is demonstrated that probably one of the most important sources of the misinterpretations and misunderstandings is the inadequate approach to the concept of electrode charge. The possibility of a general and straightforward presentation of the Gibbs adsorption equation has also been discussed.

Prediction of Interfacial Surface Energy and Effective Fracture Energy From Contaminant Concentration in Polymer-Based Interfaces

The principals of interfacial fracture mechanics and modified Gibbs adsorption equation are utilized to provide a predictive correlation for the macroscopic (effective) fracture toughness of polymer-based adhesive interfaces, exposed to varying level of contaminant concentration. The macroscopic fracture toughness measurement by double cantilever beam test exhibits a progressive deterioration with the increase of the contaminant surface concentration. The associated variation of fracture surface morphology exhibits ductile-to-brittle failure transition, caused by the contamination-induced suppression of plastic deformation within the adhesive layer. The corresponding intrinsic interfacial surface energy is extracted by finite-element simulation, employing surface-based cohesive elements. The modified Gibbs adsorption equation is utilized to correlate the contamination-induced degradation of the interfacial surface energy as a function of contaminant surface concentration. Interfacial fracture mechanics principals are applied to extend the correlation to the macroscopic fracture toughness of the interface. With additional examination of other systems, the proposed correlation may provide the basis for nondestructive evaluation of bond line integrity, exposed to different levels of contaminant.

Reactive wetting of Ni–Si alloys on graphite substrates: effects of Si and Ni

The change in equilibrium contact angle has been measured and explained based on the Gibbs adsorption equation and monolayer approximation.

Applicability of Gibbs adsorption equation and Maxwell relations to deformed solid surfaces

Revisiting derivations of Gibbs adsorption equation show its applicability to solid surfaces without limiting requirement of constant state of strain. Some attempts to use such a restriction to prove the correctness of the Shuttleworth equation have failed. Also, we have shown that the mandatory conditions for the Maxwell's relations make its inapplicable for the description of capillary and electrocapillary phenomena on solid surfaces, as they lead, if used correctly, to trivial results - known Gibbs adsorbtion equation and Lippmann electrocapillary equation. Attempts to use Maxwell's relations for the case of solid electrodes available in the literature are based on mathematical defects and, consequently, yield erroneous results.