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Have we MET?

Before anything else, I would like to congratulate on their launch as a smart mobility hub, intent on bringing all relevant stakeholders together around this crucial topic.

I will start this series of columns off with a more overarching subject, the material-energy-transportation (MET) nexus. My main reason behind this is the overlooked significance of the materiality aspect of sustainability transition in energy and transportation sectors. Additionally, I would like this first column to lead readers towards asking questions about this aspect of smart mobility. In my later columns, I will dive deeper into more specific subjects, and the technologies within each component of this nexus as is relevant for smart mobility, in an attempt to detail the sustainability perspective. To provide a few examples of what will be coming up, I will write about the material footprint of electric vehicles, the sustainability of automated and electrified heavy-duty trucks, the potential environmental impacts of fuel cell electric buses, and battery technologies that will power all our vehicles in the (near) future.

Figure 1. Schematic figure showing selected material flows (Sankey diagram) and the associated physical trade network of aluminum by life-cycle stage (physical trade flows are colored by source country, arrows are proportional to flow size, and node size is based on the sum of imports and exports) (Source:

In 1713, Hans Carl von Carlowitz first coined the term Nachhaltigkeit, meaning ‘sustainability’ in German, when he realized that unsustainable mining practices would jeopardize the supply of wood. At the time, wood was an essential resource for many economic activities from construction to mining, and was also used as a source of fuel. Therefore, as a mine administer, von Carlowitz particularly warned about the unsustainable use of timber in building and carpentry practices across Germany and brought up, for the first time, the supply risk of timber and its implications for the German economy. Hence, it was a material critical to human development that led to the spark of sustainability in both production and consumption.

Fast forward to today, the potential consequences of climate crisis urge scientists and policymakers around the world to establish a carbon-neutral economy by 2050 by rapidly phasing out the use of fossil fuels in human socioeconomic activities. The carbon-neutrality goal requires, first and foremost, the transformation of our current energy system into one that is fueled entirely by renewable energy sources. To that end, efforts with respect to transitioning to renewable energy systems have appeared high on the global sustainable development agenda and are viewed as a vital strategy to address global energy and environmental challenges in all sectors, including transportation (1). Countries all around the world have started investing heavily in wind and solar energy to substantially transform their energy and transportation infrastructure.

However, achieving such a transition is a challenging task and requires a profound understanding of the costs and benefits of deploying various transportation and renewable energy technologies. This challenge is exacerbated by the fact that enabling such a transition is of a dynamic, complex, and interconnected nature. As an example, the potential future of the energy sector will have a direct impact on the sustainability profile of the transportation sector. Likewise, the potential future of the transportation sector will determine how much energy will be needed to fuel the transportation sector. Hence, transportation must be made an integral part of the planning for renewable and sustainable energy, and vice versa. Furthermore, the future of energy and transportation enabled by new technologies emerging in these sectors will exhibit different raw material profiles, a fact that is often overlooked in their sustainability assessments. The techno-economic availability of critical materials used in these technologies is an important factor, influencing their scaling-up and deployment. To that end, this interconnectedness between transportation, energy, and materials forming the MET Nexus must be taken into consideration in transforming the transportation and energy systems worldwide.

Technologies that enable smart mobility and sustainable and renewable energy necessitate the use of advanced products that rely on the stable supply of a number of critical and precious materials. For example, rare earth elements (REEs) are extensively used in electric motors deployed in wind turbines and electric vehicles (EVs). While platinum group metals (PGMs), lithium, and cobalt are some of the indispensable materials used in mobile and stationary energy storage systems. These materials, among others, have been recently listed by the European Commission due to several reasons (2), including, but not limited to, the geographical concentration of materials (e.g. about 90% of global PGM reserves being in South Africa) (3), host metal dependence (e.g. PGMs being dependent on copper-nickel mining) (4), a lack of compatible and reliable substitutes5, and the inefficient and insufficient recycling of those materials6.

These circumstances in turn raise serious concerns over potential resource constraints that may pose a bottleneck for the deployment of needed technologies; and ultimately, for the transition to renewable energy.

These important perspectives are still missing in the current discussion on transportation and energy planning and climate crisis mitigation strategies. Considering the lifetime of large investments in renewable energy and smart mobility infrastructures, understanding of the dynamic interactions between the energy sector, transportation sector, and the raw material supply under various climate crisis mitigation scenarios is urgently needed. It is hoped that scientists and engineers in all fields will keep these aspects in mind for their work.


(1) Mancini, L.; Nuss, P. Responsible Materials Management for a Resource-Efficient and Low-Carbon Society. Resources. MDPI AG June 1, 2020, p 68.

(2) European Commission Joint Research Center. Critical Raw Materials (accessed Mar 28, 2021).

(3) Rasmussen, K. D.; Wenzel, H.; Bangs, C.; Petavratzi, E.; Liu, G. Platinum Demand and Potential Bottlenecks in the Global Green Transition: A Dynamic Material Flow Analysis. Environ. Sci. Technol. 2019.

(4) Nassar, N. T.; Graedel, T. E.; Harper, E. M. By-Product Metals Are Technologically Essential but Have Problematic Supply. Sci. Adv. 2015, 1 (3).

(5) Graedel, T. E.; Harper, E. M.; Nassar, N. T.; Reck, B. K. On the Materials Basis of Modern Society. Proc Natl Acad Sci U S A 2015, 112 (20), 6295–6300.

(6) Ciacci, L.; Vassura, I.; Cao, Z.; Liu, G.; Passarini, F. Recovering the “New Twin”: Analysis of Secondary Neodymium Sources and Recycling Potentials in Europe. Resour. Conserv. Recycl. 2019, 142, 143–152.


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