NOVELTY - A solar fuels generator comprises: ionically conductive separator (10) between first phase (20) and second phase (22); photoanode (12) that uses greater than or equal to 1 component of first phase to generate cations during operation of solar fuels generator; and cation conduit (28) positioned so as to provide pathway along which cations travel from photoanode to separator.    USE - As solar fuels generator; and for generating solar fuels (all claimed).    ADVANTAGE - The solar fuels generator provides practical solar fuels generator. Prior solar fuels generators use liquid water as feedstock. One of difficulties associated with these systems is generation of gas bubbles such as hydrogen bubbles and oxygen bubbles. The bubbles reduce contact area between water and catalysts used by these systems. Further, bubbles can refract and/or scatter incoming illumination away from photoelectrodes used in systems. As a result, bubbles can reduce efficiency of solar fuels generator. This issue can be resolved by switching from liquid feedstock to gaseous feedstock, where feedstock is carrier gas that includes water vapor. The water vapor can serve as reactant in generation of solar fuel. The use of water vapor as reactant in solar fuels generator is challenging because of mass transport issues such as whether enough water can be transported to electrodes in order to effectively produce solar fuel. But it is found that with humidified Ar(g) at 20 degrees C as feedstock to electrolyzer, electrolysis current density of 10 mA cm-2 is sustained at applied voltage of 1.6 V and current density of 20 mA cm-2 is observed at applied voltage of 1.7 V. Additionally, it is found that lower voltages are required to support particular level of current density when using water vapor in feedstock than required when liquid water was used as feedstock. Since voltage that can be achieved by solar fuels generator that uses light absorption as voltage source is around 1.5-2 V, solar fuels generator can convert water vapor to solar fuel using terrestrial solar illumination as energy source. More particularly, solar fuels generator can convert water vapor to hydrogen gas fuel without using external power source other than unconcentrated light from sun. As protons generated do not readily travel through gaseous feedstock, solar fuels generator employs cation conduits that conduct cations from photoanodes to separator. As a result, cation conduits increase efficiency of solar fuels generator using carrier gas that includes water vapor as feedstock.    DETAILED DESCRIPTION - A solar fuels generator comprises: ionically conductive separator (10) between first phase (20) and second phase (22); photoanode (12) that uses greater than or equal to 1 component of first phase to generate cations during operation of solar fuels generator; and cation conduit (28) positioned so as to provide pathway along which cations travel from photoanode to separator. The photoanode includes oxidation catalyst (24). The pathway extends from oxidation catalyst to separator, such as from separator to portion of photoanode that is distant from separator. The photoanode extends outward from first side of separator; and outward from second side of separator, where second side is opposite from first side. The cation conduit is in direct physical contact with separator, is continuous with separator, extends outward from separator along side of photoanode, includes copolymer of optionally substituted alkylene and acid (preferably sulfonic acid), and oxidation catalyst is between cation conduit and side of photoanode. The separator conducts cations. The photoanode is one of several photoanodes that each uses greater than or equal to 1 component of first phase to generate cations during operation of solar fuels generator. The cation conduit is same material as separator. The first phase is gas that includes water vapor, second phase is gas, and photoanode is configured to use water vapor to generate cations. In solar fuels generator photocathode (14) further generates solar fuel in second phase, and comprises second cation conduit positioned so as to conduct cations conducted through separator from separator to portion of photocathode that is spaced apart from separator; where photocathode includes reduction catalyst (26) between second cation conduit and side of photocathode; and second cation conduit is in direct physical contact with separator and extends outward from separator along lateral side of photocathode. An INDEPENDENT CLAIM is included for method for generating solar fuels, involving: generating cation at photoanode in gaseous first phase; and conducting generated cation through cation conduit to ionically conducting separator located between first phase and second phase.    DESCRIPTION OF DRAWING(S) - The figure shows cross section of the solar fuels generator.    Separator (10)    Photoanodes (12)    Photocathodes (14)    Photoanode light absorber (16)    First phase (20)    Second phase (22)    Photoanode catalysts (24)    Photocathode catalyst (26)    Cation conduits (28)