Photoelectrochemistry for sustainable hydrogen generation and isotope separation Eniola Sokalu 1 , Ibuki Sato 2 , Hisayoshi Matsushima 2 , Katharina Brinkert 1 1 University of Warwick, UK, 2 Hokkaido University, Japan The energy- and cost-efficient separation of isotopic components from chemical mixtures into pure or purer forms is vital for a variety of applications in the areas of medicine, wastewater treatment and chemical research. The processes involved in isotope concentration and removal - such as distillation - account for 10–15% of the world's energy consumption and are extremely inefficient [1] : currently available separation technologies suffer from low separation efficiencies and the requirement of multiple separation steps, resulting in a high energy consumption and increased costs [2,3] . One example is the separation of hydrogen (H 2 ), deuterium ( 2 H 2 or D 2 ) and tritium ( 3 H 2 or T 2 ) which is an essential process for radioactive wastewater treatment; current separation technologies are too costly and discharging contaminated water into oceans is a cheaper alternative [2,3] . Electrolysis is one of the most effective processes for hydrogen isotope separation. Due to differences in the chemical properties of hydrogen isotopes arising from their differences in mass, the hydrogen evolution reaction (HER) kinetics at the electrode surface vary greatly [4,5] . Currently, efficient semiconductor-electrocatalyst systems are developed for the photoelectrochemical generation of ‘green hydrogen’ [6] . Here, we explore the solar- assisted electrochemical hydrogen production and hydrogen isotopic separation by tailoring electrode materials and applied potentials in order to advance the understanding of HER kinetics at the photoelectrode-electrolyte interface [6-8] . We furthermore show that our photoelectrodes comprising a p-InP photocathode with integrated electrocatalysts such as Rh, Ni and Pt show higher hydrogen isotope separation factors than traditional ‘dark’ electrocatalysis systems that could open a pathway to a more sustainable route of hydrogen isotope separation. References 1. Sholl, D.S. and R.P. Lively, Seven chemical separations to change the world. Nature, 2016. 532 (7600): p. 435-437. 2. Harada, K., et al., Effects of water transport on deuterium isotope separation during polymer electrolyte membrane water electrolysis. International Journal of Hydrogen Energy, 2020. 45 (56): p. 31389-31395. 3. Matsushima, H., et al., Communication—Deuterium Isotope Separation by Solid Polymer Electrolyte Water Electrolysis. Journal of The Electrochemical Society, 2019. 166 (10): p. F566. 4. Nørskov, J.K., et al., Trends in the exchange current for hydrogen evolution. Journal of The Electrochemical Society, 2005. 152 (3): p. J23. 5. Trasatti, S., Work function, electronegativity, and electrochemical behaviour of metals: III. Electrolytic hydrogen evolution in acid solutions. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1972. 39 (1): p. 163-184. 6. Brinkert, K., et al., Advancing semiconductor–electrocatalyst systems: application of surface transformation films and nanosphere lithography. Faraday Discussions, 2018. 208 : p. 523-535. 7. Akay, Ö., et al., Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment. Advanced Science, 2022. 9 (8): p. 2105380. 8. Brinkert, K., et al., Experimental Methods for Efficient Solar Hydrogen Production in Microgravity Environment. JoVE (Journal of Visualized Experiments), 2019(154): p. e59122.
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