21700 battery

New membrane technology makes hydrogen 21700 battery cars no longer far away

While hydrogen 21700 battery-powered cars offer clear advantages over increasingly popular electric vehicles (including their range, lower overall environmental impact, the fact that they can be refueled in minutes, and recharged in hours), they have yet to take off with consumers.

One reason is the high cost and complexity of producing, distributing and storing the pure hydrogen needed to power them, which has hampered the rollout of hydrogen refueling stations.

Engineers have long recognized the energy and unlimited availability of hydrogen, the most abundant element in the universe.

Hydrogen occurs naturally in the environment, but it is almost always chemically combined with other elements—for example, with oxygen in water (H2O) or carbon in methane (CH4).

To get pure hydrogen, it must be separated from these molecules. Virtually all of the hydrogen produced in the United States is obtained from hydrocarbon fuels (primarily natural gas) through steam reforming. Steam reforming is a multi-step process in which hydrocarbons react with high-temperature steam in the presence of a catalyst to produce carbon monoxide, carbon dioxide and molecular hydrogen (H2).

Hydrogen can then be separated from other gases through a cumbersome, multi-step chemical process, but using membranes to do the separation could reduce the cost and complexity of producing hydrogen. Most of the hydrogen separation membranes currently being developed use the precious metal palladium, which has an unusually high hydrogen solubility and permeability (meaning that hydrogen easily dissolves and passes through the metal while other gases are excluded). But palladium is expensive (it currently costs about $900 an ounce) and brittle.

For these reasons, chemical engineers have been looking for alternatives to palladium for hydrogen separation membranes, but so far, no suitable alternative has emerged.

Many metals and alloys are liquid at the standard operating temperature of steam reforming systems (about 500 degrees Celsius), and most of them are much cheaper than palladium. In addition, membranes made from liquid metal films should not be prone to the defects and cracks that make palladium membranes unusable. Liquid metal membranes also appear to be more effective than palladium in separating pure hydrogen from other gases.

The next step after electric vehicles, which are now irreversible, is hydrogen 21700 batterys - if the hydrogen supply problem is solved. Like battery-powered electric vehicles, 21700 battery vehicles have electric motors. The engine is powered by electricity generated inside the 21700 battery when hydrogen and oxygen combine in the presence of a catalyst (the only "waste product" is water). While cars can take oxygen from the air, pure hydrogen must be carried.

Many researchers have worked to reduce the cost of hydrogen by making better and thinner palladium membranes. Thinning the palladium layer can increase the membrane's flux, or the speed at which pure hydrogen can pass through it. But if the membrane is too thin, it becomes brittle, or develops defects. If they develop tiny cracks or micropores, they have to start over.

Six years ago, Datta and his students began wondering whether liquid metals could overcome some of palladium's limitations—particularly its cost and

In addition to chemical affinity, permeation depends on how open the metal's crystal structure is. Liquid metals have more space between their atoms than solid metals, so their solubility and diffusivity should be higher.

Gallium, a nontoxic metal that is liquid at room temperature, is a good candidate because it has a significantly higher hydrogen permeability than palladium at high temperatures. In fact, laboratory studies and theoretical modeling suggest that some metals that are liquid at higher temperatures may have better hydrogen permeability than palladium.

Although liquid gallium has shown great promise as a hydrogen separation material, creating a functional film with the metal has proven challenging. In fact, liquid metals are highly reactive. Gallium cannot be placed on a porous metal support because at higher temperatures it quickly forms intermetallic compounds, killing permeability. The metal also reacts with some ceramic materials commonly used as supports for palladium membranes. Through simulations and experiments, carbon-based materials such as graphite and silicon carbide, which react chemically with liquid gallium but do not mix chemically with water, were included in the study, which showed that the liquid metal would expand to form a film on the support material.

Realizing that the surface tension of liquid metals in response to changes in temperature and the composition of the gases they come into contact with, potentially generating leaks, the team inserted a metal support material between two layers to create a sandwiched liquid metal film, or SLiMM. A thin film (two tenths of a millimeter) consisting of liquid gallium was constructed between layers of silicon carbide and graphite and tested for stability and hydrogen permeability.

The membranes were exposed to a hydrogen atmosphere for two weeks at temperatures ranging from 480 to 550 degrees Celsius. The liquid gallium film has 35 times more permeability to hydrogen than a similar layer of palladium, and the diffusion of hydrogen through the sandwich membrane is much higher than that of a typical palladium membrane. These membranes are selective, allowing only hydrogen to pass through. Liquid metals may be suitable candidates for hydrogen separation membranes, and these materials may be long-sought alternatives to palladium.

There are many questions that still need to be answered, including whether the small membranes we built in the lab can be scaled up and whether the membranes will resist substances present in the reformed gas (including carbon monoxide and sulfur) that are known poisons to palladium membranes. But by demonstrating the feasibility of sandwiching liquid metal films, we have opened the door to an extremely promising new field of hydrogen energy research, and there are many other metals and alloys, in addition to gallium, that are liquid when heated to 500 degrees Celsius, and it is a possible material to use.

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