There are research SOECs that have exceeded 99% efficiency, owing to the fact that the inefficiency at direct electrical conversion gets expended as heat which

There are research SOECs that have exceeded 99% efficiency, owing to the fact that the inefficiency at direct electrical conversion gets expended as heat which lowers the electrical energy levels required for water molecules to split. Basically start with an 80% efficient electrolyzed, but insulate the cell to capture all of the expended heat energy and use it to lower the need for electricity to split the cell. This is possible because of SOEC operating temperature ranges which wouldn't be possible with a PEM cell. I should also add that on the other end of the hydrogen energy cycle, production SOFCs are about 60% efficient at converting hydrogen to electricity, not 45%. And the temperatures of the waste heat are high enough to efficiently convert to electricity, bringing total electrical efficiency up to the 70-80% range. Oh, and they can use hydrocarbon fuels too.