In nature, photosynthetic organelles use sunlight to produce energy-rich compounds from water and atmospheric CO ₂ through exquisite supramolecular aggregates. Although artificial photocatalytic cycles have been shown to occur at higher intrinsic efficiencies, low selectivity and stability in water for the reduction of multielectron CO2 _prevents their practical applications. Creating water-compatible artificial photocatalytic systems mimicking the natural photosynthetic apparatus for selective and efficient solar fuel production is a major challenge. Here, we show a highly stable and efficient artificial spherical chromatophore nanomicelle system that self-assembles from Zn porphyrin amphiphiles with a Co catalyst in water for CO ₂– conversion to methane with turnover number >6600 and 89% selectivity for 30 days. The hierarchical self-assembly induced a spherical antenna effect, which could facilitate the photocatalytic process with an initial 15% solar energy-to-fuel efficiency. In addition, it has the ability to effectively reduce atmospheric CO2 _{on the} methane with high selectivity in water. (Junlai Yu)