Interfacial electron transfer reactions thermodynamics

There are two possible excited state interfacial electron transfer processes that can occur from a molecular excited state, S, created at a metal surface (a) the metal accepts an electron from S to form S+ or (b) the metal donates an electron to S to form S . Neither of these processes has been directly observed. The two processes would be competitive and unless there is some preference, no net charge will cross the interface. In order to obtain a steady-state photoelectrochemical response, back interfacial electron transfer reactions of S+ (or S ) to yield ground-state products must also be eliminated. Energy transfer from an excited sensitizer to the metal is thermodynamically favorable and allowed by both Forster and Dexter mechanisms [20, 21]. There exists a theoretical [20] and experimental [21] literature describing energy transfer quenching of molecular excited states by metals. How-... 

Thus, photoexcitation permits those electron transfer reactions to occur which are thermodynamicadly impossible in the dark, provided that the photon irradiation shifts the energy level of interfacial electrons (or holes) in the anodic (or cathodic) direction and produces the thermodynamic affinity for the reactions. 

Several important energy-related applications, including hydrogen production, fuel cells, and CO2 reduction, have thrust electrocatalysis into the forefront of catalysis research recently. Electrocatalysis involves several physiochemical environmental dfects, which poses substantial challenges for the theoreticians. First, there is the electric potential which can aifect the thermodynamics of the system and the kinetics of the electron transfer reactions. The electrolyte, which is usually aqueous, contains water and ions that can interact directly with a surface and charged/polar adsorbates, and indirectly with the charge in the electrode to form the electrochemical double layer, which sets up an electric field at the interface that further affects interfacial reactivity. 

Processes in which charge is transferred from one phase to another at an interface make up an important class of interfacial reactions. Well-known examples are the reactions which occur at the electrodes of an electrochemical cell. These are electron transfer reactions, oxidation taking place at one electrode and reduction at the other. The early study of electrochemical cells provided valuable thermodynamic information about the redox processes occurring in them. When an electrochemical cell is a source of energy, for example, a battery, chemical energy is converted to electrical energy. When electrical energy is driven into an electro-... 

Understanding chemical reactivity at liquid interfaces is important because in many systems the interesting and relevant chemistry occurs at the interface between two immiscible liquids, at the liquid/solid interface and at the free liquid (liquid/vapor) interface. Examples are reactions of atmospheric pollutants at the surface of water droplets[6], phase transfer catalysis[7] at the organic liquid/water interface, electrochemical electron and ion transfer reactions at liquidAiquid interfaces[8] and liquid/metal and liquid/semiconductor Interfaces. Interfacial chemical reactions give rise to changes in the concentration of surface species, but so do adsorption and desorption. Thus, understanding the dynamics and thermodynamics of adsorption and desorption is an important subject as well. 

Let us consider the cell in Fig. 2 that represents a closed thermodynamic system yotpp a 5. Electrochemical reactions occur in the interfacial regions ot/P and a /P between metallic phases and electrolyte. These regions have chemical, electric, and hydrodynamic properties different from those existing in the depths of the phases. Electrons are transferred across the interfaces a/y and 5/a between metallic phases. The electrode a is chosen as anode, electrode a as cathode. The external circuit connecting the terminals 1 and 2 is shown as a wire for simplicity. The following reactions take place at the interfaces in the case of the hydrogen-oxygen cell ... 

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