Carbon electrodes surface radical states

The nature of the platform also impacts on the electrochemical and photophysical properties of the interfacial supramolecular assembly (ISA). For example, the density of states within gold, platinum and carbon electrodes are different, so causing subtle changes in the rate of electron transfer across the electrode/ISA interface. In addition, in terms of the photophysical properties, the nature of the platform can radically change the excited-state properties of a molecule upon adsorption. For example, if a adsorbate is located close to (<10 nm) a metal surface and is then pumped into an electronically excited state, efficient energy or electron transfer is expected which will lead to quenching of the excited state. This process can dramatically increase the photostability of compounds that would ordinarily photodecompose in solution. 

The reasons for the deterioration of ceU performance can be distinguished in reversible and irreversible power loss. Inevitable irreversible performance loss is caused by carbon oxidation, platinum dissolution, and chemical attack of the membrane by radicals [7]. Reversible power loss can be caused by flooding of the cell, dehydration of the membrane electrode assembly (MEA), or change of the catalyst surface oxidation state [8]. If corrective actions are not started immediately, reversible effects lead to irreversible power loss that we define as degradation. In this chapter, we focus on the degradation of the catalyst layer due to undesired side reactions. 

In either case, electrochemical reduction generates radicals which lead to carbon-carbon bond formation and oligomerization. Oligomers above a critical size are insoluble and thus thin films of the electroactive metallopolymer are produced on the electrode surface. As noted above, the color of such metallopolymer films in the M(II) redox state may be selected by suitable choice of the metal. 

Firstly, the Ru(bpy)3 + is oxidized at the electrode to the Ru(bpy)3 + cation. This species is then capable of oxidizing the oxalate ( 204 ) in the diffusion layer close to the electrode surface to form an oxalate radical anion ( 204 ). This breaks down to form a highly reducing radical anion (C02 , E° = —1.9 V vs. NHE (126)) and carbon dioxide. The reducing intermediate then either reduces the Ru(bpy)3 complex back to the parent complex in an excited state, or reduces Ru(bpy)3 to form Ru(bpy)3+ that reacts with Ru(bpy)3 + to generate the excited state Ru(bpy)3 , which emits light with -620 nm. 

Proposed electrode uses polymer deposited onto conducting substrate via electrochemical polymerization. Polymer is a poly-[Me(R-Salen) type. Me represents complex compound of transition metals (Ni, Pd Co, Cu, and Fe) with at least two different oxidation states. R represents electron donating substituent such as CH3 0-, C2H5O-, HO-, -CH3 radicals. Salen represents residue of bis(salicylaldehyde) ethylenediamine in Schiff s base. Preferences for conducting substrate include carbon fiber, carbon materials with metal coatings, and metal electrodes with high specific surface areas. 

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