Morry, as I pointed out here, converting the heat accumulating due to global warming - principally in the ocean - to power and moving the balance to the deep may be the only way we can meet commitments to keeping to a less than a 2C temperature increase. To get this ocean generated energy to market however requires the conversion of electricity to an energy carrier. There are strong arguments that this carrier should be ammonia but like you I favor hydrogen because it is as much a water carrier as and energy carrier and there is a more concerted effort in the automobile industry for its use.
There is a real climate case to be made for hydrogen but as Bob points out that is undercut by steam reforming of methane. Electrolysis of sea water using OTEC power on the other hand may well be a do or die situation.
The most efficient way to produce compressed hydrogen is to perform electrolysis in deep water. When performed at a depth of 1000 meters, as would be the case in an OTEC situation, the gas arrives at the surface pressurized to 100 bar.
Full capacity OTEC -14 terawatts – using the “supergreen” electrolysis technique developed by a team from Lawrence Livermore Laboratories would also sequester about 79 billion metric tons of carbon dioxide each year.
That amount of power would produce 1.8 trillion kilograms of hydrogen through the electrolysis of 16 trillion kilograms of water and this hydrogen, when reconstituted on land through the production of energy in a fuel cell or by burning in a combustion engine, would provide every person living on the planet 600 gallons of water annually.
A widely-used model estimates the social cost of anthropogenic greenhouse gas emissions at $326 trillion by 2200.
One example of the driver for these these cost was Hurricane Patricia, the strongest Pacific Hurricane ever to reach land.
The heat that powered that and like storms when driven to a depth of 1000 meters would no longer be available to cause havoc and the coefficient of expansion of sea water at that depth is half that of the surface so sea level rise would also be reduced.
A new University of Cambridge study shows that melting permafrost will release sufficient carbon dioxide and methane to increase that cost by an additional $43 trillion.
Tropical heat moved to the deep also can no longer move to the poles to melt icecaps or permafrost.
Technology that slows or reverses global warming can not only prevent these losses it is the strongest incentive for the development of a hydrogen economy.