“…Comparison between various methods of synthesis of FA/FS. Mostly based on precious metals[21][22][23][24][45][46][47][48][49]57,58] • Poor solubility of catalysts in aqueous systems • Requires presence of base, which leads to FS and not FA • Very often, use of expensive bases • Very few water-based systems exist Heterogeneous• Low selectivity toward desired product[45,51,53,54,55,57] • Catalyst may be poisoned by one of the products (CO) Electroreduction• High energy consumption due to the slow kinetics[41,46,59] • Needs high over-potential • Low product selectivity (in water, reduction of CO 2 competes with the H 2 evolution reaction) Photoreduction• Dependent on the presence of photosensitizer[43,46,57] • Often use the ultraviolet light Hydrogen capacities of selected FS at their solubility limits at 20 °C.…”