Rejected illustrations

Artefacts, artefacts, artefacts:

(1) Colour noise (probably from JPEG compression artefacts).

(2) Artefacts, either from bad rendering or from high JPEG compression (low-quality setting).

(3) Particles/leftovers or whatever.

If you had checked your assets before submission, you would have seen the issues easily. There is even no need, as I did, to go to 100%, the artefacts are highly visible even at lower sizes.

In addition, your assets are PNG files, but there is no transparency channel present. Files with no transparency need to be submitted as JPEG files (high-quality compression, and you won't see a difference between the original file and the compressed file!).

As for the theme, I don't see a relation to Hydrogen. As working in an industry on the verge of transition to using green hydrogen in their technology, I can confirm to you that I would not have considered your assets. It simply does not represent whatever I understand as hydrogen (except for being blue… and every one knows that hydrogen is blue 🙄 ).