​​As the equation above shows, MB, which, in its oxidized form, is blue, becomes leucomethylene blue (LMB), and turns clear when reduced during the reaction with H2. The diagrams below show how the reaction between H2 and MB changes the structure of the MB molecule:

A note about using only methylene blue as an indicator for dissolved H2 gas:

H2Blue contains a common dye, methylene blue, a compound used in biological applications. But, a solution containing only methylene blue is not an effective dissolved H2 indicator. For methylene blue to function as an indicator for H2, other compounds, including a catalyst, must be added. The catalyst is, by weight, the most expensive raw material in H2Blue.  

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​​​​​​How does H2Blue detect dissolved hydrogen gas?

H2Blue detects dissolved H2 using methylene blue (MB), a compound commonly used in chemistry as an indicator and in medicine as a biological tissue dye. As an oxidizing agent, MB is known to react with dissolved molecular hydrogen (in the presence of a Platinum catalyst) to produce the clear (reduced) form of MB, leucomethylene blue (leucoMB), as follows: