OVERVIEW

The precious metals (Ru, Rh, Pd, Os, Ir, Pt) make highly effective catalysts in a wide range of chemical reactions, due to their readiness to change oxidation states and their reluctance to form recalcitrant oxides. Unfortunately, they are also some of the least abundant elements in the Earth’s crust. Over the course of the past century, many metals have been extracted from virgin ores at exponentially-increasing rates, to meet the infrastructure and industrial needs of rapidly industrializing societies in North America and Europe. Widespread implementation of new technologies, such as fuel cells, maybe strongly limited by the availability of these metals. For example, the in-use stock of platinum (Pt) needed for a fleet of 0.5 billion H2 fuel-cell cars (i.e., approx. half of the world’s current passenger vehicle fleet) would exhaust our remaining lithospheric stock of Pt in just 15 years, even if there were no competing uses for Pt.

 

Many other emerging technologies rely on uncommon elements. They may be relatively abundant but very highly distributed (e.g., the not-so-rare “rare earths” used in permanent magnets for electric vehicles and wind turbines). This results in high environmental costs for their extraction and purification. Alternately, their supply may be strongly limited by co-production, due to their occurrence as minor impurities in other metal-containing ores (e.g., In, Ga and Te used in photovoltaics and solid-state lighting). Rapid demand growth and geopolitical supply-security risks also pose impediments to large-scale deployment. Consequently, many are now widely considered to be critical elements, for which supply limitations and/or disruptions pose significant threats to our economic and/or social well-being. It is becoming urgent to minimize their use, replacing them wherever possible with Earth-abundant metals in large-scale applications. Sustainable design of processes and/or materials involving critical elements must take into account supply security, long-term availability and the environmental impact of production. How a material will be used, disposed, reused, or recycled is also key: the fate of a material through its use and end-of-life phases is largely determined during the design phase. Dissipative uses of critical elements can make material recovery prohibitively costly, and must be avoided.