Adsorption models, surface reaction, and catalyst architectures

The environment of a CO2 electroreduction (CO2ER) catalyst is intimately coupled with the surface reaction energetics and is therefore a critical aspect of the overall system performance. The immediate reaction environment of the electrocatalyst constitutes the electrical double layer (EDL) which extends a few nanometers into the electrolyte and screens the surface charge density. In this study, we resolve the species concentrations and potential profiles in the EDL of a CO2ER system by self-consistently solving the migration, diffusion and reaction phenomena using the generalized modified Poisson-Nernst-Planck (GMPNP) equations which include the effect of volume exclusion due to the solvated size of solution species. We demonstrate that the concentration of solvated cations builds at the outer Helmholtz plane (OHP) with increasing applied potential until the steric limit is reached. The formation of the EDL is expected to have important consequences for the transport of the CO2 molecule to the catalyst surface. The electric field in the EDL diminishes the pH in the first 5 nm from the OHP, with an accumulation of protons and a concomitant depletion of hydroxide ions. This is a considerable departure from the results obtained using reaction-diffusion models where migration is ignored. Finally, we use the GMPNP model to compare the nature of the EDL for different alkali metal cations to show the effect of solvated size and polarization of water on the resultant electric field. Our results establish the significance of the EDL and electrostatic forces in defining the local reaction environment of CO2 electrocatalysts.

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Non-Toxic Environment for Ferritic Nitrocarburising Process

Revista de Chimie ◽

10.37358/rc.18.9.6587 ◽

2018 ◽

Vol 69 (9) ◽

pp. 2416-2419

Author(s):

Mihai Branzei ◽

Mihai Ovidiu Cojocaru ◽

Leontin Nicolae Druga ◽

Florica Tudose ◽

Roxana Trusca

Keyword(s):

Surface Reaction ◽

Effective Solution ◽

Reaction Products ◽

Toxic Reaction ◽

Wide Range ◽

Toxic Environment ◽

Thermochemical Processing ◽

Surface Saturation ◽

Gas Molecules ◽

Toxic Components

Experimental research aimed to find a solution for replacing components with high toxicity (or generating such components as a result of reactions occurring in the environment at processing temperatures) from the environments used for ferritic nitrocarburising process (FNCP) with non-hazardous components, but extremely active during the process. In the temperature range in which this type of processing is applied (lower than the eutectoid transformation temperature in the Fe-N phase diagram), the most commonly used media are liquid or gaseous; liquid ones contain toxic components (sodium or potassium cyanates/cyanides), and gaseous ones require complex equipments. Packing is extremely rarely used, but in this case pack-mix contain toxic components (15 � 20 wt.% sodium or potassium ferrocyanide). Urea also called carbamide (CO (NH2)2) is the active component in the pack-mixing proposed to be used for FNCP. Carbamide is used in low temperature cyanidation thermochemical heat treatment (liquid FNC), together with sodium or potassium carbonates, resulting in very toxic reaction products (sodium or potassium cyanates). Compared to cyanidation, in the version proposed in the paper, the carbamide does not react with carbonates because they are not found in the composition of the environment but decomposes in the presence or absence of oxygen (by a disproportionation reaction) with the formation of some gas molecules interesting for the process. It has been concluded that the use of carbamide together with two other components, activated charcoal (having a triple role - dispersing, storage, surface saturation) and respectively ammonium chloride as surface reaction activator, is an effective solution for achieving the desired goals by applying this type of thermochemical processing to a wide range of products made of quality steels up to alloy miscellaneous steels.

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Surface reaction of adsorbed substance transported by diffusion to a plane electrode

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19653785 ◽

1965 ◽

Vol 30 (11) ◽

pp. 3785-3797 ◽

Cited By ~ 20

Author(s):

K. Holub ◽

J. Koryta

Keyword(s):

Surface Reaction ◽

Plane Electrode ◽

Adsorbed Substance

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A polycentric growth model of gallium arsenide epitaxial layers from the gas phase with simultaneous diffusion, adsorption and chemical reaction

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19882995 ◽

1988 ◽

Vol 53 (12) ◽

pp. 2995-3013

Author(s):

Emerich Erdös ◽

Jindřich Leitner ◽

Petr Voňka ◽

Josef Stejskal ◽

Přemysl Klíma

Keyword(s):

Growth Rate ◽

Gallium Arsenide ◽

Epitaxial Growth ◽

Gas Phase ◽

Surface Reaction ◽

Quantitative Description ◽

The Other ◽

Rate Equations ◽

Impact Interaction ◽

Partial Pressures

For a quantitative description of the epitaxial growth rate of gallium arsenide, two models are proposed including two rate controlling steps, namely the diffusion of components in the gas phase and the surface reaction. In the models considered, the surface reaction involves a reaction triple - or quadruple centre. In both models three mechanisms are considered which differ one from the other by different adsorption - and impact interaction of reacting particles. In every of the six cases, the pertinent rate equations were derived, and the models have been confronted with the experimentally found dependences of the growth rate on partial pressures of components in the feed. The results are discussed with regard to the plausibility of individual mechanisms and of both models, and also with respect to their applicability and the direction of further investigations.

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