The Corrosion of Carbon Black Anodes in Alkaline Electrolyte: IV . Current Efficiencies for Oxygen Evolution from Metal Oxide‐Impregnated Graphitized Furnace Blacks

Abstract

A quantitative method for determining the number of oxygenated carbon atoms in a carbon black sample was developed and applied to the study of oxygen chemisorption on graphitized furnace blacks. It was found that chemisorption of oxygen atoms produced in a low‐pressure microwave discharge of argon/oxygen results in the formation of an oxygen complex on every carbon atom exposed on the edge plane surface of these carbons. These combined procedures were then used to titrate the surfaces of a variety of graphitized furnace blacks for the number of edge atoms. The corrosion rate of these carbons was found to be directly proportional to the number of sites titrated by oxygen atom chemisorption, i.e., the number of edge atoms. The number of edge atoms exposed on the surface of graphitized furnace blacks depends on the microstructure of the precursor carbon black and the conditions of graphitization. Catalyzation of these graphitized carbons by normalNiO has little or no effect on their corrosion rate, which results in current efficiencies for oxygen evolution greater than 98%. The absence of an effect of normalNiO on the corrosion rate is attributed to the specificity of the corrosion reaction to edge plane sites and an apparent necessity for contact between normalNiO particles with edge planes for catalyzation of the corrosion reaction by normalNiO . normalNiO particles sitting on basal planes, which compose at least 90% of the surface area in these carbons, catalyze only the oxygen evolution reaction.

Selected Review of the Degradation of Pt and Pd‐based Carbon‐supported Electrocatalysts for Alkaline Fuel Cells: Towards Mechanisms of Degradation

“…The findings presented in the previous section reveal that Pt (and Pd) nanoparticles are not subjected to severe dissolution (and possible redeposition) and that their carbon support is not suffering extensive corrosion. However, Ross et al have measured (both solid and liquid) carbonates formation from carbon black degradation in alkaline environments, and in more severe conditions (higher temperatures and potentials than those considered in the present study) gaseous CO 2 evolution . In order to track such carbonate species, FTIR spectroscopy is a tool of choice.…”

“…Both processes counterbalance the passivation by solid carbonates, which is very detrimental to the carbon support durability . Graphitized carbon (more organized, with less edge atoms) was proven more robust against corrosion , , but the presence of electrocatalyst nanoparticles (usually 3d transition metals or oxides: Ni, Fe, Cr) dramatically enhances the corrosion rate of carbon . Although PGM nanoparticles have not been investigated in these earlier studies, one can postulate that, as demonstrated for acidic corrosion of PEMFC electrocatalysts , , the presence of metal (e.g., Pt) nanoparticles at the carbon surface and the alternation of high/low potential values (or of oxidizing/reducing conditions) further increases the destabilization of the carbon surface and could also destabilize the metal nanoparticles, which are immobilized at its surface .…”

“…AEM materials are far from being durable yet, even if progresses are fast [37][38][39]; concerning the electrocatalysts, as stated above, the common knowledge derived from the well-known Pourbaix diagrams is that durability issues will be lower for alkaline than for acidic-based systems. However, looking closely to these Pourbaix diagrams, one notices (for almost any element considered) that if indeed many metal oxides are stable at high pH and high potential values, some hydrated complexes may form and be stable in solution [16]; this is for example the case for noble metals like Pt (the existence of PtO 3 2- [40][41][42][43][44][45][46][47][48] or Phosphoric Acid FC [49] cathodes; (ii) the carbon support itself could also be subjected to degradation issues in the harsh environment of the alkaline fuel cell/electrolyzer, as studied by Ross et al in the 1980s [50][51][52][53] can yield solid carbonate formation and therefore passivation of the carbon surface (a positive effect in terms of durability), production of soluble carbonate ions (CO 3 2-) is possible for E < 1.4 V vs. the reversible hydrogen electrode (RHE) and T < 50°C, and gasification (CO 2 formation) is possible for E > 1.5 V vs. RHE and T > 60°C. Both processes counterbalance the passivation by solid carbonates, which is very detrimental to the carbon support durability [50].…”

Durability behavior of polymer impregnated carbon textiles in alkaline solution as CP anode

“…At the same time, the accumulation of oxygen always causes the formation of humic acid in the solution . Studies show that increasing the graphite content of the carbon causes its resistance to oxidation to carbon dioxide . In alkaline solutions (pH between 11 and 13) at high current densities, carbon dioxide accumulation prevails and at low current densities oxygen enrichment prevails …”

“…[13] Studies show that increasing the graphite content of the carbon causes its resistance to oxidation to carbon dioxide. [14] In alkaline solutions (pH between 11 and 13) at high current densities, carbon dioxide accumulation prevails and at low current densities oxygen enrichment prevails. [11] Pruckner [15] applied conductive coating as strips over and between the primary anode wires, which were fixed in concrete before.…”