MOFs in photoelectrochemical water splitting: New horizons and challenges

Abstract

Growing energy consumption with the augmentation in universal population to more than nine billion by 2050 and exhausting fossil fuel reserves necessitates a harsh revolution from non-renewable energy reservoirs to renewable energy reservoirs with zero carbon emission. In the present scenario, solar energy prompted photoelectrochemical (PEC) water splitting or “Artificial Photosynthesis” via light gripping semiconductor material, originates out as the most promising methodology in accomplishing the global energy crisis. Recent studies have amply demonstrated the potential of metal-organic frameworks (MOF) towards PEC applications. They are porous crystalline coordination polymers assembled through an appropriate choice of metal ions and multidentate organic ligands. Owing to their structural regularity and synthetic tunability, MOFs integration with PEC is considered in terms of enhancing and broadening light absorption, providing active sites and directing charge transfer dynamics. Here, we have explored MOFs role in PEC and classified them into different categories such as photosensitizers, co-catalysts, counter electrode, template and also for imparting additional stability to the electrode system. MOFs mediated PEC water splitting is promising but is still rare and in its infancy. Therefore, it is pertinent and timely to take stock of the advancements made and develop insight on the use of MOFs, as an emerging solution for the problems encountered in PEC. This review covers the basics of MOF & mainly describes various case studies done during last 10 years and providing adequate impetus to researchers for critically assessing the recent advances and challenges that are faced by scientists and researchers at large.

Conclusion

In this review, we have attempted to summarize applications of MOFs with respect to PEC splitting of water for hydrogen generation. Despite having several other available options for PEC, MOFs offer the potential to overcome one of the biggest challenges i.e., electron-hole pair recombination. This has been achieved due to their high crystal quality, favorable for achieving high charge separation efficiency and reducing electron-hole pair recombination. MOFs here have been elaborately described in terms of structure, functions, synthesis methods and modifications. MOF's function in PEC acting as cocatalyst, photosensitizer, precursor or template, counter electrode has been described in detail by citing examples from case studies. Researchers have also reported that MOFs impart additional stability to the electrode system which makes it more suitable in PEC application.

All these cited case studies have suggested that making a hybrid system of MOF is apparently the solution towards developing more efficient electrode system. Nonetheless, further explorations are still required to develop better understanding on the role and significance of MOFs in achieving efficient solar-water splitting and hydrogen generation in PEC cell. Impending area of research is to harness all or most of the properties of MOFs such as template, photosensitization, co-catalytic nature etc. in one hybrid system which will definitely be helpful in taking full advantage of MOF system towards increasing the overall PEC efficiency.

To be cited as:

Runjhun Dutta , Rohit Shrivastav, Manju Srivastsava, Anuradha Verma, Sakshi Saxena, Neeraj Kumar Biswas, Vibha Rani Satsangi, Sahab Dass, MOFs in Photoelectrochemical Water Splitting: New Horizons and Challenges, International Journal of Hydrogen Energy, 2021, 47, 8, 5192-5210.