The Hydrogen Color Wheel: A Primer

The international dialogue about climate change and the "net zero" world now includes a focus on hydrogen as an abundant source of energy useful in myriad ways (refining, fertilizer production, motive power, etc.) with potentially zero climate-harmful emissions. For those of us who took Chemistry 101 in high school, we know that hydrogen is by far the most abundant element in the Universe, representing an estimated 70 to 75 percent of all known matter. While that is an awesome number (giving rise to the common student question "How do we know that?"), the fact is that, here on Earth, hydrogen does not exist as a "free" gas—it is present here only in combination with other elements, notably oxygen, carbon, and nitrogen. Thus, to capture hydrogen for use in multiple applications, it must be separated from the paired substances (most commonly water (H2O) and natural gas (CH4)).