The economics of direct vs two-step water splitting
S. Himmelstein | June 21, 2021
Two ways to make hydrogen from seawater and green electricity. The pathway on the left shows direct seawater splitting where only one device is required. In the pathway on the right, the seawater is first desalinated by reverse osmosis and then the water splitting is performed. Source: Matthias Driess et al.
How comparable are the economics of direct seawater splitting versus a two-step process for hydrogen production? Researchers in Germany examined the thermodynamic requirements, process energy consumption, capital costs, and the price of freshwater produced by each hydrogen production route to determine which is more cost-effective.
The two-step scenario in which purification by reverse osmosis is followed by splitting in a conventional water electrolyzer is the more economically attractive option. Direct seawater splitting is disadvantaged by relatively short electrolyzer service life, the impacts of seawater composition changes, and problems posed by biofouling, solids precipitation, corrosive oxidation species and membrane malfunctions.
Direct seawater electrolyzers must be operated at a high flow velocity and require a higher level of maintenance relative to two-step systems, factors that lead to increased capital and operating costs.
The research conducted by scientists from Technische Universität Berlin and Fritz-Haber-Institut der Max-Planck-Gesellschaft is published in Energy & Environmental Science.
You could then take the hydrogen produced and combine it with carbon dioxide and produce methane and water via Sabatier process, thereby mitigating CO2 and producing fuel and clean water and oxygen....