Scientists at the Weizmann Institute of Science in Rehovot, Israel, have devised a scheme that gets round the problem of dangerous and expensive hydrogen infrastructure, and makes possible 100% green cars that emit only water from their tailpipe. By reacting water with the element boron, their system produces hydrogen that can be burnt in an internal combustion engine or fed to a fuel cell to generate electricity. The only by-product is boron oxide, which can be removed from the car, turned back into boron, and used again. What's more, they plan to do this in a solar-powered plant that is completely emission-free.