A Report by the APS Panel on Public Affairs and the Materials Research Society coined the term “energy-critical element” (ECE) to describe a class of chemical elements that currently appear critical to one or more new, energy related technologies.

“Energy-related systems are typically materials intensive. As new technologies are widely deployed, significant quantities of the elements required to manufacture them will be needed. However, many of these unfamiliar elements are not presently mined, refined, or traded in large quantities, and, as a result, their availability might be constrained by many complex factors. A shortage of these energy-critical elements (ECEs) could significantly inhibit the adoption of otherwise game-changing energy technologies. This, in turn, would limit the competitiveness of U.S. industries and the domestic scientific enterprise and, eventually, diminish the quality of life in the United States.”

According to the APS and MRS report several factors can contribute to limiting the domestic availability of an ECE:

• The element may not be abundant in the earth’s crust or might not be concentrated by geological processes
• An element might only occur in a few economic deposits worldwide, production might be dominated by and, therefore, subject to manipulation by one or more countries – the United States already relies on other countries for more than 90% of most of the ECEs identified in the report
• Many ECEs have, up to this point, been produced in relatively small quantities as by-products of primary metals mining and refining. Joint production complicates attempts to ramp up output by a large factor.
• Because they are relatively scarce, extraction of ECEs often involves processing large amounts of material, sometimes in ways that do unacceptable environmental damage
• The time required for production and utilization to adapt to fluctuations in price and availability of ECEs is long, making planning and investment difficult

This report was limited to elements that have the potential for major impact on energy systems and for which a significantly increased demand might strain supply, causing price increases or unavailability, thereby discouraging the use of some new technologies.

The focus of the report was on energy technologies with the potential for large-scale deployment so the elements they listed are energy critical:

• Gallium, germanium, indium, selenium, silver, and tellurium – employed in advanced photovoltaic solar cells, especially thin film photovoltaics.
• Dysprosium, neodymium, praseodymium, samarium and cobalt – used in high-strength permanent magnets for many energy related applications, such as wind turbines and hybrid automobiles.
• Gadolinium (most REEs made this list) for its unusual paramagnetic qualities and europium and terbium for their role in managing the color of fluorescent lighting. Yttrium, another REE, is an important ingredient in energy-efficient solid-state lighting.
• Lithium and lanthanum, used in high performance batteries.
• Helium, required in cryogenics, energy research, advanced nuclear reactor designs, and manufacturing in the energy sector.
• Platinum, palladium, and other PGEs, used as catalysts in fuel cells that may find wide applications in transportation. Cerium, a REE, is also used as an auto-emissions catalyst.