Sustainability and Techno-Economic Analysis of a Power-to-Hydrogen Process Employing Low and High-Temperature Water Electrolysis

An integrated power-to-low-carbon hydrogen process is proposed in which a natural gas–fired Allam–Fetvedt (AF) supercritical carbon dioxide (CO2) cycle supplies electricity and process water to low- and high-temperature electrolyzers based on proton exchange membrane (PEM), anion exchange membrane (AEM), and solid oxide electrolyzer (SOE) technologies. The novelty of this study is the development of a unified process-level framework that combines Aspen HYSYS simulation, techno-economic analysis, and multidimensional sustainability assessment to compare AF-integrated PEM, AEM, and SOE hydrogen production pathways under the same 437 MW-net power basis. Detailed steady-state simulations were carried out in Aspen HYSYS for an AF cycle producing approximately 795 MW of gross electrical power and 437 MW of net electrical power after internal and auxiliary power consumption. The resulting 437 MW net output was used as the fixed electrical input for the PEM, AEM, and SOE configurations to ensure a consistent comparison among the three electrolysis pathways. The resulting mass and energy balances were coupled with a methodological sustainability assessment framework that aggregates 44 indicators grouped into four dimensions: material, energy, environmental, and economic performance. Techno-economic analysis included capital expenditure (CAPEX), operating expenditure (OPEX), levelized cost of hydrogen (LCOH), and 25-year cash-flow metrics at a 10% discount rate with oxygen (O2) by-product credit. All integrated schemes achieved high material and environmental efficiencies, with normalized scores exceeding 95% and approximately 97%, respectively. The AF–electrolyzer system was internally water self-sufficient, while the O2 by-product supplied approximately 25–30% of the AF cycle oxygen demand. Energy efficiency was moderate but technology-dependent, with AF+SOE outperforming AF+PEM and AF+AEM due to higher electrolysis efficiency and stronger heat-integration potential. The main limitation was economic, as LCOH varied between approximately 4.3 and 7.3 $ kg−1 hydrogen (H2) across optimistic and pessimistic CAPEX/OPEX scenarios. Overall sustainability scores of 81.4%, 80.3%, and 83.0% for AF+PEM, AF+AEM, and AF+SOE, respectively, show that all three pathways are viable low-carbon hydrogen options, while AF+SOE provides the strongest combined energy, environmental, and techno-economic performance.