In this article, we report a detailed study on co-production of H-2 and syngas on La0.9Ca0.1FeO3- (LCF-91) membranes via water splitting and partial oxidation of methane, respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm-thick dense membrane at 990 degrees C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 mol/cm(2)center dot s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H-2/CO=2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO2, depending on the oxygen permeation flux. (c) 2016 American Institute of Chemical Engineers AIChE J, 62: 4427-4435, 2016