Recent developments in the design of photoreactors for solar energy conversion from water splitting and CO2 reduction

In recent decades, increasing interest has been devoted to improving the methods for solar energy conversion using water splitting and CO2 reduction for solar fuel development. Herein, we discuss the historical background, present the current status, and expose development prospects to summarize and highlight the design of photoreactors. First, we discuss how converting CO2 greenhouse gas to renewable fuels by using sustainable sunlight energy can simultaneously solve the problems of global warming and sustainable energy shortage. Several types of photoreactors for photocatalytic CO2 reduction and CO2 hydrogenation for realizing solar fuels have been developed extensively. Among them, an optical-fiber photoreactor, a monolith photoreactor, and an internally illuminated monolith photoreactor have received considerable attention recently. Second, we show how the design of novel twin photoreactor systems has great potential for solar energy conversion from water splitting. Combining water splitting and CO2 hydrogenation to mimic photosynthesis is expected to play an important role in the future. Third, we demonstrate how a twin photoreactor also offers a new approach to producing solar fuels and simultaneously degrading organic wastewater. We believe that effectively combining H-2 production to hydrogenate CO2 and organic wastewater treatment is a promising green technology. Finally, we propose critical challenges and prospects for the design of photoreactors. This review highlights the need to give more attention to the design of photoreactors for solar energy conversion from water splitting and CO2 reduction.