That's only true for CO2.

Burning hydrogen does release other emissions. Especially NOx

>Burning H2 does not produce carbon dioxide (CO2) emissions. >That is good news for the climate.

>However, hydrogen combustion produces other air emissions. And that scientific fact is the untold story in this aggressive industry plan, one that could turn green H2 into ghastly H2.

>The bad news is that H2 combustion can produce dangerously high levels of nitrogen oxide (NOx). Two European studies have found that burning hydrogen-enriched natural gas in an industrial setting can lead to NOx emissions up to six times that of methane (the most common element in natural gas mixes).[17],[18] There are numerous other studies in the scientific literature about the difficulties of controlling NOx emissions from H2 combustion in various industrial applications.[19],[20]

>Even the Trump Administration’s Department of Energy “Hydrogen Program Plan” identifies H2 combustion as a significant problem. It states that additional research is needed on a host of emissions control issues around H2 combustion. The point DOE makes is that at very low levels of H2 blending, the NOx emissions levels might be controllable. But at higher levels, it is not only difficult to control NOx emissions, but the technologies that have been developed to attempt to control those higher NOx levels remain unproven.[21] That research is years off.

https://www.cleanegroup.org/hydrogen-hype-in-the-air/