Accelerating global energy consumption makes the development of clean and renewable alternative energy sources indispensable. Nanotechnology opens up new frontiers in materials science and engineering to meet this energy challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Since the Nobel Prize winning research on graphene by Geim and Novoselov, considerable efforts have been made to exploit graphene as an energy material, and tremendous progress has been achieved in developing high-performance devices for energy conversion and energy storage. This article reviews recent progress in the research and development of graphene materials for advanced energy-conversion devices, including solar cells and fuel cells, and energy-storage devices, including supercapacitors and lithium-ion batteries, and discusses some challenges in this exciting field.

Rapid changes in energy availability lead to the question of whether the sustainable availability of energy implies the sustainable availability of materials and vice versa. In particular, many researchers assume that materials can be produced from any resource type, irrespective of scarcity, by providing enough energy. We revisit this issue here for two reasons: (1) To avoid significant disruptions in daily life, no more than a few percent of total energy production and materials usage can be diverted to support a transition to new energy sources. (2) Such a transition could also be problematic if it requires large quantities of materials that are byproducts of other large-scale production cycles, as any increase in the production of a byproduct typically requires an almost proportional increase in the production of the primary product. In turn, increased production of the primary product could require materials and energy expenditures that are too large to be practical. Both limitations have to be taken into account in future energy planning.

During this century, humankind must deal with increasing demand for energy and the growing impact of burning fossil fuels. Nuclear power, which presently produces 14% of global electricity, is a low-carbon-emissions alternative. However, the sustainability of nuclear power depends on the amounts of uranium and thorium available, the economics of their recovery from ore deposits, and the safety and security of nuclear materials. Unlike combustion of hydrocarbons, which determines the amount of fuel needed for a given amount of energy, nuclear reactions can create additional fissile isotopes. Hence, the choice of nuclear fuel cycle profoundly affects the size of the nuclear resource, as well as nuclear waste management and the risk of proliferation of nuclear weapons. We argue that uranium resources, identified and yet to be discovered, could sustain increases in nuclear power generation by a factor of two or three through the end of this century, even without advanced closed-fuel-cycle technologies.