Introduction to the metal-free photo/electrocatalysts for sustainable energy solutions themed collection

Reiner Sebastian Sprick

Seb obtained his PhD from the University of Manchester. Following this he first worked at the University of Liverpool as a research associate, then as a research coordinator. In 2020, he moved to the University of Strathclyde where he is currently employed as a senior lecturer. His research focuses on the use of conjugated polymers for applications in sustainability, in particular the use of these materials as photocatalysts for water splitting and carbon dioxide reduction.

Menny Shalom

Menny received his PhD in chemistry in 2013 from Bar-Ilan University. Then, he joined the Max Planck Institute of Colloids and Interfaces, Germany, as a postdoc. From 2014 to 2016, he was appointed as a group leader at MPI, and since the end of 2016, he has been a professor at the Ben-Gurion University of the Negev, Israel. His group focuses on synthesizing new materials for energy conversion applications, mainly photo-electrochemical cells and electrocatalysts.

Xinchen Wang

Xinchen is Vice President of Fuzhou University, China, and Director of the State Key Laboratory of Photocatalysis on Energy and Environment. He earned his PhD from the Chinese University of Hong Kong in 2005. He was a JSPS postdoctoral fellow at the University of Tokyo (2006) and an Alexander von Humboldt fellow at the Max Planck Institute (2007–2012). A fellow of the Royal Society of Chemistry (2015), Changjiang Scholar (2016), and member of Academia Europaea (2024), he is a pioneer in carbon nitride photocatalysis, advancing applications in overall water splitting, CO2 reduction, organosynthesis and more.

Photo(electro)catalysis is a promising research area for sustainable energy production and chemical production in the context of sustainability and climate action in particular. The use of light-driven photocatalysis also has huge potential to help with environmental remediation, making it potentially more effective and cheaper at scale.¹

There is an urgent need for renewable and storable energy, which will be essential to overcome the intermittency of renewable energy.² For this, hydrogen has been identified as the ideal candidate, in particular if produced directly from sunlight which can potentially minimise losses compared to photovoltaic-systems coupled to electrolysers. Other energy carriers, such as hydrogen peroxide are also very interesting in this context. It is also clear that we will continue to rely on carbon-based fuels, for example in aviation given the large energy and volume densities required, which will be challenging to achieve using batteries or hydrogen. Enabling circularity of carbon dioxide is therefore an important goal of researchers. Perhaps equally important will be the transition to the sustainable production of carbon-based chemical feedstocks. The transition away from internal combustion engines will also reduce demand for carbon-based fuels (i.e., petrol).² As a consequence of this, refineries might become unprofitable, which in turn will also reduce the availability of a large number of other chemicals that are being produced from refineries, such as ethylene, propylene, butadiene, benzene, toluene, xylene. The sustainable production of carbon-based feedstocks is therefore essential to provide us with the resources to maintain our quality of life. Finally, the production of fertiliser using the Haber–Bosch process has been an absolute cornerstone for humankind’s existence – without it the world's population would not be sustained. Given that approximately 2% of all energy worldwide annually is consumed in this process it is also essential to find alternative methods that use less energy and do not emit greenhouse gases.

Many of these challenges have been explored using light-driven processes enabled by photocatalysts. Typically, these photocatalysts are inorganic³ but in recent years more and more research has been published using organic semiconductors.^4,5 These metal-free photo(electro)catalysts offer potentially low-cost and efficient solutions. The properties of these materials can be tuned by changing the building-blocks utilised in their synthesis, which enable the use of a very large experimental space. As these are carbon-based materials, they are potentially also more sustainable and the processability of some of these material classes might enable facile scale up in the future. Example material classes include carbon nitrides,⁶ boron carbon nitrides,⁷ triazine-based frameworks,⁸ covalent organic frameworks,⁹ conjugated microporous polymers and unbranched conjugated polymers as well as composites of organic materials,^4,5 and biohybrid systems.¹⁰

This themed collection in Sustainable Energy & Fuels aims to highlight the unique properties of metal-free photo- and electrocatalysts, and their application in energy carrier production, such as photocatalytic water splitting (https://doi.org/10.1039/D4SE01777C), carbon dioxide reduction (https://doi.org/10.1039/D5SE00142K), organic transformation reactions (https://doi.org/10.1039/D5SE00146C) as well as environmental remediation (https://doi.org/10.1039/D4SE01751J).

Acknowledgements

R. S. S. thanks the University of Strathclyde for financial support through The Strathclyde Chancellor's Fellowship Scheme and a Research Collaborations grant from the International Science Partnerships Fund (ID 1203758747). The grant is funded by the UK Department for Science Innovation and Technology in partnership with the British Council. X. W. is thankful for financial support from the National Natural Science Foundation of China (U24A20567 and 21961142019). MS thanks the Israel Council for Higher Education (VATAT) project, “Next-Gen Tandem Solar Systems: A Collaborative Center for Advanced Solar Energy Research in Israel” for financial support.

References

1. UV-visible Photocatalysis for Clean Energy Production and Pollution Remediation: Materials, Reaction Mechanisms, and Applications, ed. X. Wang, M. Anpo and X. Fu, Wiley-VCH GmbH, Weinheim, 2023.
2. E. T. C. Vogt and B. M. Weckhuysen, Nature, 2024, 629, 295–306.
3. A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38, 253–278.
4. Y. Wang, A. Vogel, M. Sachs, R. S. Sprick, L. Wilbraham, S. J. A. Moniz, R. Godin, M. A. Zwijnenburg, J. R. Durrant, A. I. Cooper and J. Tang, Nat. Energy, 2019, 4, 746–760.
5. M. Z. Rahman, M. G. Kibria and C. B. Mullins, Chem. Soc. Rev., 2020, 49, 1887–1931.
6. D. Bhanderi, P. Lakhani and C. K. Modi, RSC Sustainability, 2024, 2, 265–287.
7. E. J. Sohn, B.-M. Jun, S.-N. Nam, C. M. Park, M. Jang, A. Son and Y. Yoon, Chemosphere, 2024, 349, 140800.
8. S. Li, Y. Mao, J. Yang, Y. Li, J. Dong, Z. Wang, L. Jiang and S. He, Heliyon, 2024, 10, e32202.
9. X. Li, Q. Dong, Q. Tian, A. Sial, H. Wang, H. Wen, B. Pan, K. Zhang, J. Qin and C. Wang, Mater. Today Chem., 2022, 26, 101037.
10. Y. Yang, L.-N. Liu, H. Tian, A. I. Cooper and R. S. Sprick, Energy Environ. Sci., 2023, 16, 4305–4319.

---