The Promise of Solid Lubricants for a Sustainable Future.

There's no question that lubricants will become more crucial in a world where technology plays an ever-more-important role. Lubricants save vast amounts of energy and material resources by reducing friction and increasing the lifetime of devices. It is no surprise that the lubrication industry is one of the largest in the world. The climate crisis demands solutions independent of non-renewable fossil energy, from which most of the liquid lubricants are extracted. Solid lubricants are the focus of the research community because they provide extremely low friction with a potentially much lower environmental impact. They are used when the operating conditions of machines do not allow the use of liquids, such as in a high temperature or vacuum environment, or when contamination mitigation is critical. The future of solid lubricants is bright. Can they truly be a direct substitute for liquid lubricants in certain applications, as many researchers claim, or will they be used only for applications where operating conditions are too harsh? In this perspective, the status and prospects of several classes of solid lubricants for greener and more effective lubrication are critically reviewed, with the hope that they can help us achieve the sustainability goals for the planet.