Hydrogen from water

More than two hundred years ago, English chemist William Nicholson stuck two wires in a bucket of water and turned on the juice. Bubbles began breaking the surface above each lead—oxygen at the positive, hydrogen at the negative. He didn’t yet have the words anode and cathode to describe them, that came later from Michael Faraday who also gave us electrolysis to describe the reaction. From the Greek èlektron, “amber” (the fossilized tree resin known for electrostatic properties) and lysis, “to loosen or set free”—the application of electric current breaks the bond that holds H2 to O.

Through the first half of the 20th century, electrolysis was the sole means of isolating hydrogen from the compound molecules where nature holds it. Water electrolysis was supplanted later in the century by coal gasification and natural gas reforming that now account for 95% of world hydrogen supply. But every kilogram of hydrogen pulled from fossil sources puts 10 to 25 kilograms of carbon in the sky. Only recently has the advent of low-carbon energy and fuel markets caused electrolysis to be optimized above megawatt capacity and costs reduced to enable industrial-scale production.