NOVELTY - The illumination-driven apparatus comprises a separator (708) having a first side and a second side that is opposite to the first side, an oxidation catalyst (704) present on the first side of the separator, a reduction catalyst (706) present on the second side of the separator, a source of water vapor permitted to contact the first side of the separator and the oxidation catalyst, a light absorber (702), first and second inlet ports, first and second outlet ports, and a chamber configured to contain a reagent. The separator is configured to be permeable to an ionic reaction moiety.    USE - The illumination-driven apparatus is useful for generating a chemical fuel and molecular oxygen from a reaction medium containing water vapor (claimed).    ADVANTAGE - The illumination-driven apparatus ensures efficient and continuous generation of the chemical fuel and molecular oxygen without resorting to electrical energy sources external to the electrolysis cell.    DETAILED DESCRIPTION - The illumination-driven apparatus comprises a separator (708) having a first side and a second side that is opposite to the first side, an oxidation catalyst (704) present on the first side of the separator, a reduction catalyst (706) present on the second side of the separator, a source of water vapor permitted to contact the first side of the separator and the oxidation catalyst, a light absorber (702), first and second inlet ports, first and second outlet ports, and a chamber configured to contain a reagent. The separator is configured to be permeable to an ionic reaction moiety and configured to be impermeable to molecular moieties so as to separate a first molecular moiety present on the first side from a second molecular moiety present on the second side. The oxidation catalyst is configured to oxidize water to produce molecular oxygen. The reduction catalyst is configured to reduce a substance to produce a chemical fuel. The light absorber is configured to: absorb terrestrial solar illumination having an intensity of less than or equal to 1 kW/m2; provide electrons at a voltage sufficient to drive a desired chemical half-reaction at the reduction catalyst; and accept electrons so as to drive another desired chemical half-reaction at the oxidation catalyst. The light absorber and the separator are present in mechanical contact so as to form a monolithic structure. The first inlet port is configured to permit the introduction of water vapor into the apparatus. The first outlet port is configured to allow molecular oxygen to exit the apparatus. The chemical fuel is hydrogen and a carbonaceous fuel, which is a compound represented as C(M)H(2N)O(2M+N-2P) in which M is an integer giving the number of moles of carbon dioxide consumed, N is an integer giving the number of moles of water consumed, and P is an integer giving the number of moles of oxygen produced in a chemical reaction that produces moles of C(M)H(2N)O(2M+N-2P). The ionic reaction moiety is hydrogen ion (H+) and hydroxyl ion (OH-). The chamber is configured to permit the reagent to contact the second side of the separator and the reduction catalyst. The second inlet port is configured to permit the introduction of the reagent into the chamber. The second outlet port is configured to permit the removal of the chemical fuel from the chamber. An INDEPENDENT CLAIM is included for a method of generating a chemical fuel and molecular oxygen from a reaction medium containing water vapor.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of an illumination-driven apparatus.    Light absorber (702)    Oxidation catalyst (704)    Reduction catalyst (706)    Separator (708)    Flux. (710)