Artificial photosynthesis. In the context of the Chameleon Suit study, artificial photosynthesis refers to a variety of technical possibilities leading to the recovery of a significant fraction of the EVA astronaut’s respiratory oxygen requirements from exhaled carbon dioxide and exhaled or evaporated water vapor. Like natural photosynthesis, oxygen recovery processes are expected to be powered by incident sunlight on the surface of the spacesuit system since this is the only power source that has been identified which is sufficiently energetic and compatible with the mass and volume requirements for EVA mobility. If successfully developed, they would enable significant reduction in the oxygen storage tanks in the EVA life support backpack, the sole remaining portion of the system untouched by other Chameleon Suit technologies. They will also reduce the need for mission expendables to support XXX. To realize this possibility, technology must be developed which can replicate the ability of natural photosynthesis to apply the energy in incident sunlight to the reduction of CO2 in the presence of water to form O2 and organic compounds. Desirable characteristics of natural photosynthesis, operation at normal ambient temperatures consistent with human comfort, operation with low partial pressure of carbon dioxide, and ability to release oxygen to a relatively high O2 partial pressure atmosphere must be preserved. At the same time, substantial gains in process intensity (i.e. the net amount of oxygen recovered per unit of area, system mass, and time) will be required to achieve practicality in a spacesuit system. In addition, adaptation is required to move the process from an operating environment in which sunlight, the carbon dioxide source, and atmospheric oxygen sink are all available at a single common surface (or surfaces intimately connected to one another as in a leaf), to one in which the sunlit surface may be exposed to a vacuum and must be thermally isolated from atmospheric carbon dioxide source and oxygen sink. The replication of photosynthetic processes in biomimetic engineered systems is believed to be a practical possibility in the near future based on the high level of active research in this area, and rapid progress in understanding the materials and mechanisms involved. The intense interest in photosynthesis and research activity aimed at understanding and mimicking it is illustrated by the publication of a summary article entitled “Photosynthesis and the Web” (Xxx, Xxxx...
Artificial photosynthesis. The aim of the artificial photosynthesis research is to obtain an “artificial leaf”, a device able to perform the same hydrolysis reaction as in the natural system in order to obtain hydrogen using water as the raw material. This device needs to have different modules to mimic and perform the various stages of the photochemistry as in the photosynthetic organisms. An antenna system is needed for efficient light harvesting. A charge separator complex is crucial to stabilize the radicals formed upon photoinduced electron transfer and to delay the charge recombination. A robust and efficient catalyst is also necessary to perform the water oxidation cycle. Moreover, the complete device, the artificial leaf, must be self-healing in order to reduce the possible light damage along the whole process [18]. During the last two decades, important scientific progress has been obtained in the field of light harvesting units and charge separation systems [19-21]. However, one of the bottlenecks in artificial photosynthetic research is the chemical design of a synthetic water splitting catalyst able to perform the multi electron oxidation reaction at high turnover number and frequency, with moderate overpotential and high current density.
