Pretty sure it usually produces chlorine gas and caustic soda, but I could be wrong.
But if they manage to get H2 from it then the sodium, oxygen, and chlorine have to bind into something else than usual I guess.
"Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change"
https://pubs.acs.org/doi/10.1021/es0701816
It was mind blowing for me at the time! Subsequent approaches to accelerated silicate weathering like Project Vesta dropped the chemical component and just used mechanical crushing of rocks to accelerate weathering. The all-mechanical approach is less complicated and energy intensive.
Biological processes are far more efficient at fixing carbon into biomass and using unlimited free solar energy. Bio CCS.
You'd need a hell of a lot of chlorine to compensate for current methane injection, though.
It's the same electrolysis process used today in swimming pools to generate chlorine. The hydrogen evaporates, the chlorine ends up in the water, and the chemical reaction ends up producing the same salt it started with. You don't have to add salt[0] and the chlorine pretty quickly evaporates and breaks down in sunlight if you don't put cyanuric acid in the water to bind it.
Mostly it could be ignored, though if the chlorine level got high enough it would kill the organic things.
[0] except for losses due to other reasons than chlorine generation