Electrolysis can actually be done at above 70% efficiency. 80% efficiency methods are available. You unfortunately lose some additional energy when compressing the Hydrogen for storage, or when you turn it into Methane for storage.
Carbon capture is also possible at low energy cost, from seawater, as described in a set of research articles published by the USNRL through the 2010s. The Google X Project "Foghorn" failed to develop this in an economically feasible manner, but my view is that that's more a measure of the mis-pricing of fossil fuels than of the method itself.
The resulting liquid hydrocabons are largely perfect analogues of petrol, kerosene (jet fuel) or deisel, and require no compression or refrigeration.
Carbon capture is also possible at low energy cost, from seawater, as described in a set of research articles published by the USNRL through the 2010s. The Google X Project "Foghorn" failed to develop this in an economically feasible manner, but my view is that that's more a measure of the mis-pricing of fossil fuels than of the method itself.
The resulting liquid hydrocabons are largely perfect analogues of petrol, kerosene (jet fuel) or deisel, and require no compression or refrigeration.