This week in science: Metallic hydrogen, electricity without heating, and more

This week in Science is a review of the most interesting scientific achievements and scientific discussions of the week.

Diamonds compressing molecular Hydrogen to create atomic metallic Hydrogen. Credit: R. Dias and I.F. Silvera.

This week marked the first-time atomic metallic hydrogen has ever made its appearance on Earth, as reported by Harvard University scientists in the journal Science. Thomas D. Cabot, Isaac Silvera, and Ranga Dias managed to synthesize this new material by increasing pressure on it.

As can be seen in the image below, transparent, insulator, molecular hydrogen is first transformed to "black hydrogen", a semiconductor, and then to atomic and metallic hydrogen. To achieve this result, it was necessary to squeeze a small sample of hydrogen at 495 gigapascals, more pressure than at the center of Earth. As stated by Professor Isaac Silvera:

"This is the holy grail of high-pressure physics. It's the first-ever sample of metallic hydrogen on Earth, so when you're looking at it, you're looking at something that's never existed before."

The atomic hydrogen was already theoretically predicted as were some of its properties, which could be revolutionary if proven true. The theory predicts it would be metastable, which means that if you take the pressure off, it will stay metallic. Because it is also predicted that metallic hydrogen could act as a superconductor at room temperature, it could be used to revolutionize energy transmission. As stated by Professor Silvera:

“As much as 15 percent of energy is lost to dissipation during transmission, so if you could make wires from this material and use them in the electrical grid, it could change that story."

Finally, metallic hydrogen could be used as the most powerful rocket propellant ever discovered and help transform how we explore space. According to the scientists, metallic hydrogen when converted back to molecular hydrogen would release enough energy to be almost four times more powerful than current propellants.

It is important to point out, though, that some physicists are skeptical about the Harvard team's result. The team has not yet repeated the experiment, a common procedure in science, so there is only one measurement of the reflectivity of the sample at high pressure, an indication that it is a metal. Further measurements conducted by the team and repeated by others around the world will be necessary to confirm this achievement.

But metallic hydrogen wasn’t the only material to make headlines this week. According to a study led by scientists from the Lawrence Berkeley National Laboratory and the University of California, Berkeley, electrons in vanadium dioxide can conduct electricity without conducting heat.

The scientists have found that metallic vanadium dioxide doesn’t respect the Wiedemann-Franz law, which states that a good conductor of electricity is also a good conductor of heat. According to physicist Junqiao Wu, principal investigator:

“This was a totally unexpected finding. It shows a drastic breakdown of a textbook law that has been known to be robust for conventional conductors. This discovery is of fundamental importance for understanding the basic electronic behavior of novel conductors.”

Vanadium dioxide (VO₂2) nanobeams in a false-color scanning electron microscopy image. Credit: Junqiao Wu and Berkeley Lab.

This phenomenon occurs with this material because electrons move through it “in unison with each other, much like a fluid, instead of as individual particles like in normal metal.” Since there is no randomness in the motion, the heat transfer is decreased in vanadium dioxide. This property could allow the use of this material in thermoelectric systems that convert heat released from engines into electricity.

Some advancements on carbon-free energy were also made this week. Scientists at the Lawrence Livermore National Laboratory have conducted a thorough review of open challenges for building efficient photoelectrochemical cells (PECs). These cells are responsible for absorbing sunlight and driving water-splitting reactions, from which hydrogen is generated and can be used as fuel.

A schematic illustration of a photoelectrochemical cell for water splitting. Credit: Peter Allen and The Institute for Molecular Engineering, University of Chicago.

This research was published in the January 9 edition of the journal Nature Materials and, according to scientist Anh Pham:

“Despite steady efforts and some breakthroughs, no single material has yet been found that simultaneously satisfies the efficiency and stability required for the commercialization of PEC hydrogen production technology.”

It happens that another study from a team of scientists from Pacific Northwest National Laboratory may have found such a material. The team has modified the composition of magnetite, the mineral used in compass needles, to capture visible sunlight and convert this light energy into electrical current.

Structural diagram of the modified magnetite. Credit: Pacific Northwest National Laboratory.

It was necessary to modify a sample of magnetite (Fe₃O₄) so exactly one third or the iron (Fe) in it is replaced with chromium (Cr). This would result in an unusual semiconducting phase capable of absorbing light in the visible portion of the solar electromagnetic spectrum.

Finally, Spanish scientists have created new hardware capable of 3D printing functional human skin. According to them, it creates each of the layers of the skin one above the other, by depositing plasma with skin cells in a precise geometry. Such configuration allows the cells to proliferate and create the skin. The lab-grown skin could then be used in transplants and laboratory tests of products.

Unfortunately, it’s not yet possible to use 3D printing to create other organs that aren’t flat as skin for use in humans.

The development of the technology necessary to 3D print other organs would be very welcome for those who reject other techniques being developed for creating organs. For example, scientists from Salk Institute in La Jolla, California, are among other work groups trying to inject human stem cells into pig embryos to create “chimeras” whose tissue would be partly human.

The first attempt by this group was reported in the journal Cell and turned out to not be successful since few human cells survived in the animals. It is important to clarify that none of the animals were allowed by the scientists to develop for more than a few weeks and that none of them have been born.