Platinum black

Key takeaways

Platinum black belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Platinum black to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Platinum black from memory before moving on to harder problems.

Reference excerpt

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.

Uses

Thin film electrode 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.

Fuel cell membrane catalyst 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.

Catalytic ignition of flammable gases 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), oxidation of which is particularly well catalyzed by platinum black.

Manufacturing of platinum black powder 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.

Process of platinization of platinum metal 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). 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). Another author 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. 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. 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 metal sponge 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.

It is made of a mass of platinum particles with the following characteristics:

Platinum (Pt) content: ≥99.9% Iron (Fe) content: ≤0.005% Specific surface area: 40–60 m2/g Particle size: <10 nm Dangerous code: F Dangerous level: R11 Security level: S16 UN numbers: 3089 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.

Potential of platinized platinum versus shiny platinum 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. The reason for this is not perfectly clear, although several explanations have been proposed.

See also Standard hydrogen electrode Overpotential Adams' catalyst (platinum dioxide) Raney nickel (catalyst)

References

Worked examples

Example 1 — a first encounter with Platinum black

Start with the simplest possible case. Write down what Platinum black claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Platinum black before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Platinum black ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Platinum black

In research: Platinum black appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Platinum black in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Platinum black is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrodes, Hydrogen technologies, Hydrogenation catalysts, so understanding it makes those chapters shorter.
In everyday life: Look for Platinum black outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Platinum black in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Platinum black means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Platinum black out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Platinum black in simple terms?

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.

Why does Platinum black matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Platinum black?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Platinum black.