Overall Solar-Driven Water Splitting with Organic Semiconductor Bulk Heterojunction Based Devices

Developing inexpensive, robust, and efficient light harvesting material systems is imperative to make direct solar-to-fuel energy conversion by photoelectrochemical (PEC) or heterogeneous photocatalytic (PC) approaches economically viable. In recent years, organic semiconductors have emerged as promising materials for application in this field due to their molecular tunability and scalable processability. The bulk heterojunction (BHJ) concept, which has proven successful in the field of organic photovoltaics, offers a promising route to inexpensive and high-performance production of solar hydrogen by the PEC or PC approach.<br/>In this presentation, the design and performance of organic semiconductor-based BHJ photoelectrodes for both solar-driven water reduction^[1] and oxidation^[2] will be discussed. The integration of a BHJ photoanode and photocathode into one bias-free tandem PEC device for overall water splitting (OWS)^[3] and the use of a BHJ deposited on a novel, transparent porous gas-diffusion electrode for H₂ production in the gas-phase^[4] are also presented. In addition, an approach utilizing BHJs in a PC sheet assembly for OWS is introduced. We demonstrate OWS at ca. 1% solar-to-H₂ efficiency, and discuss insights gained regarding the stability of BHJs for PEC or PC application. Finally, the challenges toward the further development of BHJ-based systems for industrially viable OWS are examined.<br/><br/><b>Significant recent publications:</b><br/>[1] L. Yao, N. Guijarro, F. Boudoire, Y. Liu, A. Rahmanudin, R. A. Wells, A. Sekar, H.-H. Cho, J.-H. Yum, F. Le Formal, K. Sivula, <i>J. Am. Chem. Soc</i>. <b>2020</b>, <i>142</i>, 7795.<br/>[2] H.-H. Cho, L. Yao, J.-H. Yum, Y. Liu, F. Boudoire, R. A. Wells, N. Guijarro, A. Sekar, K. Sivula, <i>Nat. </i><i>Catal.</i> <b>2021</b>, <i>4</i>, 431.<br/>[3] D. Zhang, H. Cho, J.-H. Yum, M. Mensi, K. Sivula, <i>Adv. </i><i>Energy Mater.</i> <b>2022</b>, 2202363.<br/>[4] M. Caretti, E. Mensi, R. Kessler, L. Lazouni, B. Goldman, L. Carbone, S. Nussbaum, R. A. Wells, H. Johnson, E. Rideau, J.-H. Yum, K. Sivula, <i>Adv. Mater.</i> <b>2023</b>, 2208740.