Hydrogen is the simplest and lightest of the elements. When combined with oxygen in a fuel cell, hydrogen produces heat and electricity with only water as a by-product. It's now used in fuel cell vehicles. In this episode, we'll look at other ways that hydrogen can help reduce the carbon dioxide emissions that drive climate change. It could replace conventional batteries for storage and retrieval of energy. And new ultra-cold magnetic compounds are being used to create magnetic refrigerators that can convert hydrogen from a gas to a liquid. We'll also see how a new home robot can help the elderly manage their medications.