The Linde AG logo on a liquid hydrogen tanker truck taking a fuel delivery at the Linde hydrogen plant in Leuna, Germany, on Tuesday, July 14, 2020.Rolf Schulten | Bloomberg | Getty ImagesHydrogen is the simplest element, and the most abundant substance in the universe.When hydrogen burns, it generates energy in the form of heat, with water as a by-product. That means energy created from hydrogen generates no atmosphere-warming carbon dioxide, making it one of many potential energy sources that could help reduce carbon emissions and slow global warming.But creating hydrogen and transforming it into a useful format requires energy — and that energy is not necessarily renewable. That process is also inefficient and expensive compared with other forms of energy, renewable or not. Many critics say the hydrogen industry a way for oil and gas giants to stall the adoption of pure…