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C O L O U R K E 'Y

The following type of technology, in theory, goes back nearly 50 years. It is now making steady, but slow, progress over the past few years. As usual, these advances tend to be over-hyped; this is not the first such material arrangement of this type under investigation.

From Synthesis and Spectral Properties of Nanocrystalline V-Substituted In₂S₃ [indium sulphide],
a Novel Material for More Efficient Use of Solar Radiation. Image: acs.org

“Current photovoltaic (PV) devices and photocatalysts can use solar light through a process in which the absorption of one photon by a semiconductor leads in the latter to the promotion of an electron from the valence band (VB) to the conduction band (CB) with the subsequent production of electric current or chemical reactions. Within this mechanism, photons with energy lower than the forbidden band gap width E_g cannot be used. In recent years it has been proposed that the insertion of an additional level (the intermediate band, IB) in the forbidden gap could provide an additional path for attaining the same final excitation result through the absorption of two photons with energy lower than E_g, similarly to what happens in natural photosynthesis [...]” [Quoted from acs.org]

“Today's solar cells absorb only visible light, wasting the infrared that makes up half of the Sun's output that reaches Earth. But a new material developed in Spain can absorb infrared too, and should make it possible to hike the power solar cells can produce, say researchers.

“Conventional solar cells are based on a semiconductor such as silicon. But their inability to soak up infrared gives them a theoretical absorption limit of just over 40% of solar energy. In practice, they only absorb about 30%..”
—
“Their idea was to create a kind of energy "stepping stone". Instead of having to jump to the higher energy level in one go, electrons can absorb a low-energy photon and then wait at an intermediate energy level until another arrives to let it complete the trip.”

Semiconductor elements in the Periodic Table. Image: jxcrystals.com

“The new material, though, can harness both visible and infrared photons, so it has a theoretical maximum efficiency of 63%, its creators say, and should give significantly better real-world performance [than silicon].” [Quoted from newscientist.com]

Original article available here for $25!
Long abstract available here.

background briefings
photovoltaics (solar cells)

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claim of producing hydrogen locally at normal temperatures - also, algae to petrol/gasoline

It’s getting ever more difficult to keep up with the progress in material sciences, and with checking the veracity of the deluge of claims. Here are two from this week.

“Currently available electrolyzers, which split water with electricity and are often used industrially, are not suited for artificial photosynthesis because they are very expensive and require a highly basic (non-benign) environment that has little to do with the conditions under which photosynthesis operates.” [Quoted from web.mit.edu]

I’m not sure how he intends to store the hydrogen in any useful quantity.

“Sapphire Energy announced today they have produced renewable 91 octane gasoline that conforms to ASTM certification, made from a breakthrough process that produces crude oil directly from sunlight, CO2 and photosynthetic microorganisms, beginning with algae.”
“Sapphire’s scalable production facilities can grow easily and economically because production is modular, transportable, and fueled by sunlight - not constrained by land, crops, or other natural resources.”
—
“Products and processes in this category differ significantly from other forms of biofuel because they are made solely from photosynthetic microorganisms, sunlight and CO2; do not result in biodiesel or ethanol; enhance and replace petroleum-based products; are carbon neutral and renewable; and don’t require any food crop or agricultural land.” [Quoted from sapphireenergy.com]

speculative: claimed new fuel-cell battery combination - which i don’t fully get!
[Original article in the Royal Society of Chemistry Journal.]

Claims to be taken with caution.

This item is being reported in various places with a degree of confusion. The technology is alleged to produce a useful energy at a density higher than petrol (gas) or diesel, and at an order of magnitude (ten times) higher than lithium battery technology.

The claim seems to be that this fuel-cell battery combination can be charged like an ‘ordinary’ battery and, when the charge is run down, the combination becomes a fuel cell. The fuel cell/battery cannibalises energy in some manner from its vanadium-boride anode, as it then acts as a fuel-cell. The anode can then be replaced., for instance at a garage in the manner of a petrol fill-up, and the anode can then be returned to functionality.

There are also suggestions that other combinations, including lithium and aluminium-[aluminum]-based systems, can be developed in this direction.

I get the impression that the reports I have seen so far are written by authors who do not fully understand the claims, and I certainly do not have a good outline grasp of the system!

So, I am linking this report for others to look at, without much confidence that I understand it!

“Energy capacity comparison of gasoline (petrol), hydrogen and electrochemical energy sources. The intrinsic energy of gasoline yields a maximum practical efficiency of 30% due to Carnot and friction losses. Air fuel cells do not have this Carnot inefficiency, and have practical capacities instead constrained by overpotential losses, and the requisite volume of the air anode and all other cell components. Volumetric capacity of liquid H2 is constrained by its density of 0.0708 kg L-1. Shaded superimposed on solid, colors, compare intrinsic and practical capacities.”

related material
Fuel cells and battery-powered vehicles

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