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Platinum black (Pt black) is a fine powder of platinum with good catalytic properties. The name of platinum black is due to its black color. It is used in many ways; as a thin film electrode, a fuel cell membrane catalyst, or as a catalytic ignition of flammable gases for "self-lighting' gas lamps, ovens, and stove burners.
Platinum black is widely used as a thin film covering solid platinum metal, forming platinum electrodes for applications in electrochemistry. The process of covering platinum electrodes with such a layer of platinum black is called "platinization of platinum." The platinized platinum has a true surface area much higher than the geometrical surface area of the electrode and, therefore, exhibits action superior to that of shiny platinum.
Platinum black powder is used as a catalyst in proton-exchange membrane fuel cells. In common practice, the platinum black is either sprayed using an ultrasonic nozzle or hot pressed onto the membrane or gas diffusion layer. A suspension of platinum black and carbon powder in ethanol-water solutions serves to optimize the uniformity of the coating, electrical conductivity, and in the case of application to the membrane, to prevent dehydration of the membrane during the application.
Historically many "self-lighting" gas lamps, ovens, and stove burners used platinum black to catalyze the oxidation of a small amount of gas, lighting the device without a match or spark. This works particularly well for producer gas, town gas, and wood gas which contain a substantial fraction of hydrogen gas (H2) which is particularly well catalyzed by platinum black.
Platinum black powder can be manufactured from ammonium chloroplatinate by heating at 500 °C in molten sodium nitrate for 30 minutes, followed by pouring the melt into water, boiling, washing, and reduction of the brown powder (believed to be platinum dioxide) with gaseous hydrogen to platinum black. [1]
Before platinization, the platinum surface is cleaned by immersion in aqua regia (50% solution, i.e., 3 volumes of 12 mol/kg of HCl, 1 volume of 16 mol/kg HNO3, 4 volumes of water). [2]
Platinization is often conducted from water solution of 0.072 mol/kg of chloroplatinic acid and 0.00013 mol/kg of lead acetate, at a current density of 30 mA/cm2 for up to 10 minutes. The process evolves chlorine at the anode; the interaction of the chlorine with the cathode is prevented by employing a suitable separation (e.g., a glass frit). [2]
Another author [1] recommends electroplating with the current density of 5 mA/cm2 while reversing the polarity every 30 seconds for 15 minutes.
After platinization, the electrode should be rinsed and stored in distilled water. The electrode loses its catalytic properties on prolonged exposure to air. [ citation needed ]
The process for electroplating platinum black on platinum was invented by Lummer and Kurlbaum when they were unable to reproduce Langley's lampblack-covered platinum foils for bolometers. [3] [4] [5] [6] When the platinum black did not adhere to the cathode, they found that adding around 1% copper sulfate to the chloroplatinic acid in the electrolyte improved the results. Later, they found a much smaller proportion of lead acetate worked better than the copper sulfate.
Platinum sponge is a porous, grayish-black form of platinum that can adsorb a large amount of gas, such as hydrogen or oxygen gas, allowing it to be used as a catalyst in many gas reactions such as the oxidation of ammonium. It can also be used for the ignition of combustible gases. It is used as the raw material for electronic instrument, chemical industry, and precision alloys. It can also be used as a surface active agent. It is soluble in aqua regia and is formed from a mass of metallic particles.
| CAS | 7440-6-4 |
| Formula Weight | 195.08 |
| Purity | Pt≥99.9% |
| Appearance | Black powder |
| Melting point | 1769°C |
| Boiling Point | 3827°C |
| Density | 5.78 g/mL |
| Solubility | Soluble in aqua regia; Insoluble in water and inorganic acid |
It is made of a mass of platinum particles with the following characteristics:
It is prepared by dipping asbestos into chloroplatinic acid or ammonium chloroplatinate. The substance is then burned to produce platinum sponge. Alternatively, it can be made by strongly heating ammonium chloroplatinate. Its catalytic properties vary depending on the specifics of the manufacturing. [1]
In hydrogen saturated hydrochloric acid, the shiny platinum electrode is observed to assume positive potential versus that of platinum black at zero net current (+ 340 mV at room temperature). With the temperature increasing to 70 °C, the difference in potentials dropped to zero. [7] The reason for this is not perfectly clear, although several explanations have been proposed.
Catalysis is the increase in rate of a chemical reaction due to an added substance known as a catalyst. Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst.
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish platina, a diminutive of plata "silver".
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential. The word "lysis" means to separate or break, so in terms, electrolysis would mean "breakdown via electricity".
In electrochemistry, the standard hydrogen electrode, is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be 4.44 ± 0.02 V at 25 °C, but to form a basis for comparison with all other electrochemical reactions, hydrogen's standard electrode potential is declared to be zero volts at any temperature. Potentials of all other electrodes are compared with that of the standard hydrogen electrode at the same temperature.
Proton-exchange membrane fuel cells (PEMFC), also known as polymer electrolyte membrane (PEM) fuel cells, are a type of fuel cell being developed mainly for transport applications, as well as for stationary fuel-cell applications and portable fuel-cell applications. Their distinguishing features include lower temperature/pressure ranges and a special proton-conducting polymer electrolyte membrane. PEMFCs generate electricity and operate on the opposite principle to PEM electrolysis, which consumes electricity. They are a leading candidate to replace the aging alkaline fuel-cell technology, which was used in the Space Shuttle.
Adams' catalyst, also known as platinum dioxide, is usually represented as platinum(IV) oxide hydrate, PtO2•H2O. It is a catalyst for hydrogenation and hydrogenolysis in organic synthesis. This dark brown powder is commercially available. The oxide itself is not an active catalyst, but it becomes active after exposure to hydrogen whereupon it converts to platinum black, which is responsible for reactions.
Electrolysis of water is using electricity to split water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture would be extremely explosive. Separately pressurised into convenient 'tanks' or 'gas bottles', hydrogen can be used for oxyhydrogen welding and other applications, as the hydrogen / oxygen flame can reach approximately 2,800°C.
Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6). Hexachloroplatinic acid is highly hygroscopic.
Ammonium hexachloroplatinate, also known as ammonium chloroplatinate, is the inorganic compound with the formula (NH4)2[PtCl6]. It is a rare example of a soluble platinum(IV) salt that is not hygroscopic. It forms intensely yellow solutions in water. In the presence of 1M NH4Cl, its solubility is only 0.0028 g/100 mL.
Platinum on carbon, often referred to as Pt/C, is a form of platinum used as a catalyst. The metal is supported on activated carbon in order to maximize its surface area and activity.
Palladium black is a coarse, sponge-like form of elemental palladium which offers a large surface area for catalytic activity. It is used in organic synthesis as a catalyst for hydrogenation reactions.
Gas diffusion electrodes (GDE) are electrodes with a conjunction of a solid, liquid and gaseous interface, and an electrical conducting catalyst supporting an electrochemical reaction between the liquid and the gaseous phase.
A membrane electrode assembly (MEA) is an assembled stack of proton-exchange membranes (PEM) or alkali anion exchange membrane (AAEM), catalyst and flat plate electrode used in fuel cells and electrolyzers.
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.
Water oxidation is one of the half reactions of water splitting:
Proton exchange membrane(PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes. The PEM electrolyzer was introduced to overcome the issues of partial load, low current density, and low pressure operation currently plaguing the alkaline electrolyzer. It involves a proton-exchange membrane.
Alkaline water electrolysis is a type of electrolyzer that is characterized by having two electrodes operating in a liquid alkaline electrolyte solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH). These electrodes are separated by a diaphragm, separating the product gases and transporting the hydroxide ions (OH−) from one electrode to the other. A recent comparison showed that state-of-the-art nickel based water electrolyzers with alkaline electrolytes lead to competitive or even better efficiencies than acidic polymer electrolyte membrane water electrolysis with platinum group metal based electrocatalysts.
Vertically aligned carbon nanotube arrays (VANTAs) are a unique microstructure consisting of carbon nanotubes oriented with their longitudinal axis perpendicular to a substrate surface. These VANTAs effectively preserve and often accentuate the unique anisotropic properties of individual carbon nanotubes and possess a morphology that may be precisely controlled. VANTAs are consequently widely useful in a range of current and potential device applications.
Anion exchange membrane(AEM) electrolysis is the electrolysis of water that utilises a semipermeable membrane that conducts hydroxide ions (OH−) called an anion exchange membrane. Like a proton-exchange membrane (PEM), the membrane separates the products, provides electrical insulation between electrodes, and conducts ions. Unlike PEM, AEM conducts hydroxide ions. The major advantage of AEM water electrolysis is that a high-cost noble metal catalyst is not required, low-cost transition metal catalyst can be used instead. AEM electrolysis is similar to alkaline water electrolysis, which uses a non-ion-selective separator instead of an anion-exchange membrane.
