The two-step cycle for solar-thermochemical fuels production and thermochemical energy storage benefits from low oxygen partial pressure in the high-temperature thermal reduction step. To be practical, low oxygen partial pressures must be reached by energetically efficient and economically affordable methods-a challenge currently not met by either mechanical vacuum pumping or by inert gas sweeping. To address this challenge, we have examined a promising, thermally-driven surface adsorption/desorption approach. Providing that appropriately designed materials can be identified as expected, this approach would substantially advance solar-thermochemical fuel production (water and carbon dioxide splitting), thermochemical energy storage, and related technologies.