50 Shades of Hydrogen: A Perspective on Definitions in Science and Public Communication

Discussions about the transition to hydrogen in various applications have become an important topic in recent years. A key factor for an effective transition is public acceptance of hydrogen technologies. However, the increase in acceptance depends, among other things, on individual knowledge about the hydrogen colors and the linked hydrogen production pathways currently under discussion. In communications, colors such as green, grey and blue are used to distinguish hydrogen sources. With new research, additional colors have become necessary. Unfortunately, there is no unified definition for the colors. The aim of this perspective is to identify the most frequent hydrogen colors used by scientists and the public, derive open definitions and propose a solution to a representation problem. The general use of hydrogen colors in communication and the implications on public acceptance are briefly outlined. We then identified definitions for colors associated with a specific pathway and discussed some discrepancies between science and media use. To make better use of the existing colors, more open definitions were formulated. We point out the representation problem with shades of a color and provide a connection between the assigned color and a view-independent RGB color code as proposal. The derived definitions can be used to unify communication in science and public media.