CC BY 4.0Mütter, FelixFelixMütterBoškoski, PavlePavleBoškoskiMegel, StefanStefanMegelHochenauer, ChristophChristophHochenauerSubotić, VanjaVanjaSubotić2026-01-122026-01-122026https://publica.fraunhofer.de/handle/publica/502753https://doi.org/10.24406/publica-699810.1016/j.fuel.2025.13799210.24406/publica-69982-s2.0-105024982412Same-hardware, stack-scale evidence for PtX syngas routes is scarce. We quantify, on identical solid-oxide hardware, how operating conditions affect stack voltage and specific electricity demand to guide selection between steam electrolysis, paired downstream with RWGS, and direct co-electrolysis. We report new stack-level steam-electrolysis data and benchmark them against our previously published co-electrolysis dataset on the same five-cell electrolyte-supported stack and test rig. Measurements are non-overlapping with aligned operating windows and a single analysis pipeline. A structured design-of-experiments with regression yields sensitivities to current density, fuel-side composition/flow, and temperature. Electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), and in-plane temperature mapping provide mechanistic context for ohmic, charge-transfer, and transport contributions. Within the tested window, co-electrolysis shows stronger voltage sensitivity to current density and the air-outlet setpoint. Differences in specific electricity demand are modest per stack yet material at plant scale. Holding hardware and analysis constant, we deliver a reproducible benchmark that supports route selection and informs thermal and current-density control in commercial PtX plants.entrueCo-electrolysisDesign of Experiments (DoE)Hydrogen ProductionPower-to-X (PtX)Solid Oxide Electrolysis (SOE)Steam Electrolysis600 Technik, Medizin, angewandte Wissenschaften::620 Ingenieurwissenschaftenjournal article