Recent challenges and scope in tandem cells for unassisted overall water splitting

Hydrogen is an efficient and cleaner source of energy and has potential to meet future energy demands. Hydrogen production by solar-driven unassisted water splitting methodology is a mandatory step to achieve this goal. Several strategic approaches are reported to improve efficiency by modifying the surface layers of the electrodes to enhance surface kinetics while some focused on improving stability of photo-electrodes in highly saline water medium and many have worked upon improving the catalyst reaction in the process of recombination of holes and electrons. Still challenges such as poor efficiency, low stability, small solar to hydrogen ratio, over-potential, rate of evolution and high cost are limiting the construction of PEC water splitting system. Herein, we briefly summarize the recent developments in solar to hydrogen conversion technology utilizing different mechanisms over the period including metal oxide, nitrides, monolithic configuration, photo-catalysts, electro-catalysts, surface modulation layers and low quantum yield.