The invention provides for the integration of a CO-consuming process, such as a gas fermentation process, with a CO.sub.2 electrolysis process. The invention is capable of utilizing a CO.sub.2-comprising gaseous substrate generated by an industrial process and provides for one or more removal modules to remove at least one constituent from a CO.sub.2-comprising gaseous substrate prior to passage of the gaseous substrate to a CO.sub.2 electrolysis module. The invention may further comprise one or more pressure modules, one or more CO.sub.2 concentration modules, one or more O.sub.2 separation modules, and/or an H.sub.2 electrolysis module. Carbon conversion efficiency is increased by recycling CO.sub.2 produced by a CO-consuming process to the CO.sub.2 electrolysis process.

A method for photothermal synthesis gas production. The method comprises feeding methane and carbon dioxide into a photothermal reactor, the photothermal reactor comprising a catalyst. The catalyst comprises a metal organic framework (MOF) derived nanocomposite oxide catalyst, the MOF derived nanocomposite oxide catalyst being grown on titanium dioxide (TiO.sub.2) quantum dots.