This old article explains the basics

The harmful gas, the byproduct of decay, has been accumulated for centuries. Can we work to remove the hydrogen sulfide content of the Black Sea or at least reduce its concentrations? Scientists have been for quite some time mulling this question on the look out for solutions. All the more so that the otherwise harmful gas is rich in hydrogen that has been increasingly considered as an alternative fuel option with a future.

“I had the idea of using hydrogen sulfide not for the direct extraction of hydrogen through electrolysis as anybody would expect, but rather the direct use of hydrogen sulfide for energy. At the next stage this energy could be used to carry out electrolysis from seawater for obtaining hydrogen.”

And here’s a review of most recent research: https://www.sciencedirect.com/science/article/pii/S036031992305886X