Search for surface structural effects in electrocatalysis. II. Platinized platinum electrodes

1973 ◽  
Vol 26 (12) ◽  
pp. 2587 ◽  
Author(s):  
T Biegler
Keyword(s):  
Particle Size ◽  
Specific Activity ◽  
Platinum Electrodes ◽  
Reversible Hydrogen Electrode ◽  
Small Particle Size ◽  
Structural Effects ◽  
Hydrogen Atoms ◽  
Hydrogen Electrode ◽  
Platinized Platinum ◽  
Adsorptive Properties

The adsorptive properties of platinized electrodes, as indicated by cyclic voltammetry, depended on the potential of platinum electrodeposition. Electrodes deposited above 0.05 V v. reversible hydrogen electrode were similar to smooth platinum, while those deposited at negative potentials showed anomalous behaviour, particularly with regard to hydrogen sorption. Measurements with such electrodes over a range of sweep rates showed slow sorption of about two hydrogen atoms in excess of the usual fast adsorption of one hydrogen atom per surface platinum atom. Freshly electrodeposited platinum had a specific activity for methanol oxidation of one-quarter to one-half that of smooth platinum. The lower activity was attributed to the effects of disordered surface structure and/or small particle size. Anodic-cathodic cycling produced surface recrystallization and activities close to that for smooth platinum.

SOME ABNORMAL HYDROGEN ELECTRODE REACTIONS

1959 ◽  
Vol 37 (1) ◽  
pp. 213-221 ◽  
Author(s):  
D. J. G. Ives
Keyword(s):  
Current Flow ◽  
Reducing Power ◽  
Open Circuit ◽  
Theoretical Treatment ◽  
Platinum Electrodes ◽  
Thermal Deactivation ◽  
Reaction Step ◽  
Hydrogen Atoms ◽  
Hydrogen Electrode ◽  
Hydrogen Overpotential

A brief account is given of experiments in which gold electrodes, as a result of thermal deactivation in hydrogen, change from a state in which their behavior in relation to the hydrogen evolution reaction is normal to a state characterized by high positive rest potentials, greatly enhanced overpotentials which increase progressively during current flow, and which decay slowly on open circuit, generating potential–time curves which resemble desorption isotherms.Conclusions based on these phenomena are supported by the results of experiments with poisoned platinum electrodes, which not only behave similarly but are also shown to retain reducing power for a limited time on open circuit.It is suggested that electrodeposited hydrogen atoms may sometimes evaporate from an electrode into solution by a mechanism involving the participation of molecule-ions. A recent theoretical treatment of hydrogen overpotential can be extended to allow for the occurrence of such a final reaction step.

scholarly journals Hydrogen overvoltage and the reversible hydrogen electrode

1936 ◽  
Vol 157 (891) ◽  
pp. 423-433 ◽  
Keyword(s):  
Alternative Mechanism ◽  
Hydrogen Ions ◽  
Hydrogen Atoms ◽  
High Activation ◽  
Hydrogen Electrode ◽  
Potential Region ◽  
Reverse Transfer ◽  
Platinized Platinum ◽  
Hydrogen Overvoltage ◽  
Free Hydrogen

There are two fairly sharply contrasted methods by which hydrogen is liberated in electrolysis. At high overvoltage electrodes Tafel found that the current and electrode potential were related by i = ke - ε V/2 k T , a relation more recently confirmed by Bowden. These electrodes are not reversible and there is no evidence that the process H 2 → 2H + + 2ε can occur to any appreciable extent at potentials accessible to observation. Even at ordinary bright platinum, which has a fairly low overvoltage, Armstrong and Butler found that the ionization of hydrogen occurred to only a slight extent in the region between the reversible hydrogen potential and the potential at which oxygen begins to be formed. On the other hand, reversible hydrogen potentials have long been known at platinized platinum and similar electrodes, and it has been found that bright platinum and similar metals can be “activated” in various ways, whereby it is brought into a condition in which the reversible hydrogen potential can be realized. In this state the hydrogen overvoltage is low and at small displacements from the reversible value the potential varies linearly with the current, i. e ., V = V 0 — ki This relation can be accounted for on the assumption that there are two processes at the reversible electrode which are influenced exponentially by the potential, but in opposite directions. The theories of overvoltage which have been put forward have been concerned mainly with the behaviour of high overvoltage electrodes. In Gurney’s theory the potential determining process was the transfer of electrons from the metal to the hydrogen ions in the solution. As Gurney pointed out, this process is essentially irreversible, for the reverse transfer of electrons from either free hydrogen atoms or molecules cannot occur to an appreciable extent in the same potential region. Horiuti and Polanyi have suggested an alternative mechanism in which the primary process is the transference of hydrogen ions to adsorption positions at the surface of the metal, in the course of which neutralization occurs. This process may under some circumstances be reversible, but on the assump­tions made has a high activation energy of 20-30 k. cals.

Search for surface structural effects in electrocatalysis. I. Smooth platinum electrodes

1973 ◽  
Vol 26 (12) ◽  
pp. 2571 ◽  
Author(s):  
T Biegler
Keyword(s):  
Methanol Oxidation ◽  
Specific Activity ◽  
Chemical Activation ◽  
Linear Sweep Voltammetry ◽  
Methanol Oxidation Reaction ◽  
Platinum Electrodes ◽  
Oxidation Of Methanol ◽  
Crystalline Surface ◽  
Cold Worked ◽  
Adsorptive Properties

Platinum electrodes were pretreated in various ways with the aim of producing surfaces of different structure. The adsorptive properties were studied using linear sweep voltammetry, and the activity for the anodic oxidation of methanol was determined using a multi-pulse potential program. Although chemical etching and different kinds of heat treatment altered the hydrogen adsorptive properties of platinum, the specific activity for methanol oxidation was not significantly affected. A relationship between the shapes of anodic voltammograms in the hydrogen region and at the start of the oxide region was noted and used in deducing the nature of the adsorbed oxygen-containing species and its involvement in the methanol oxidation reaction. Electro- chemical activation of cold-worked electrodes was attributed to the removal, by anodic dissolution, of a structurally disturbed layer of surface platinum atoms of lower activity than a crystalline surface. The activity of platinum for methanol oxidation was concluded to be a property of a well-ordered crystalline surface, independent of orientation.

Dose schedule of Rasa Aushadhis

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Dr. Jambla Neha ◽  
Saroch Vikas ◽  
Johar Smita
Keyword(s):  
Particle Size ◽  
Oral Mucosa ◽  
Small Particle ◽  
Dose Schedule ◽  
The Body ◽  
Small Particle Size ◽  
Inherent Property ◽  
Ayurvedic Drugs ◽  
Modern Era

Rasashastra deals with the Rasa Aushadhis, the drugs of metallic and mineral origin. Mercury is used in most of the Rasaaushadhis. The toxicity of Mineral and metallic preparations are reduced to such an extent by various procedures of Shodhana, Marana etc. that Mercury converts its inherent property of toxicity into medicinal property. Rasa Aushadhis works quickly on the body because due to their small particle size, their absorption starts from the oral mucosa itself. The action of drugs depends largely upon the Anupana i.e. the vehicle for the drug. Rasacharayas have mentioned various Rasa preparations like Bhasmas, Parpati, Pottali, Manduras, Karpooras etc. along with their doses, dose schedule and Anupana / Sahapana etc. The principles of Rasaaushadhis when correlated in modern era are found to be scientifically accurate. We may say that Rasacharyas had already mastered the science of nanotechnology, purification, action of metabolic catalysts, biotransformation and preservation of medicines. The Ayurvedic drugs can be harmful for our body when not administered in proper dosage as per mentioned in classic literatures.

scholarly journals Design and characterization of oil-in-water nanoemulsion for enhanced oil recovery stabilized by amphiphilic copolymer, nonionic surfactant, and LAPONITE® RD

RSC Advances ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1952-1959
Author(s):  
Yi Zhao ◽  
Fangfang Peng ◽  
Yangchuan Ke
Keyword(s):  
Particle Size ◽  
Nonionic Surfactant ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Small Particle ◽  
Amphiphilic Copolymer ◽  
Good Stability ◽  
Small Particle Size ◽  
Oil In Water

Emulsion with small particle size and good stability stabilized by emulsifiers was successfully prepared for EOR application.

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