(Invited) The Tortuous History of Photoelectrochemistry and Photocatalysis after the Fujishima Discoveries

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In this talk, I will attempt to chart the numerous twists and turns the twin fields of photoelectrochemistry and photocatalysis have undergone since the momentous discovery by Fujishima and Honda that anodic films of titania could split water into hydrogen and oxygen under sunlight. Interestingly, these authors did not discover this phenomenon, nor did they pioneer the fact that irradiated titania (or other oxide semiconductor) films could promote the photocatalytic degradation of environmental pollutants to mineralized products. There are also question marks on whether in the original Nature paper, these authors (and their junior collaborators) truly demonstrated that water was being split into hydrogen and oxygen. Instead, claims have been made that what they reported was a regenerative cell involving the generation and subsequent reduction of dioxygen instead of the photoinduced reduction of protons into hydrogen. (However, these authors did demonstrate, in a subsequent paper in the J. Electrochem. Soc., that hydrogen gas indeed was evolved in the correct stochiometric ratio with oxygen.) Nonetheless, it must be said that the Fujishima-Honda reports truly sparked intense interest in this solar conversion strategy and spawned a veritable, bonanza for the field, and indeed for the parent disciplines of photochemistry and electrochemistry. Other twists and turns that affected the evolution and growth of these twin fields including the discovery that most narrow bandgap semiconductors were photoelectrochemically unstable, and subsequent attempts to tackle this issue, will be discussed. Finally, the field of solar water splitting is truly at a pivotal point right now and its very future is murky. Avenues that may instead prove to be more profitable will be identified. Acknowledgements . The author thanks his numerous collaborators over the years. This work was primarily supported by the National Science Foundation UTA/NU Partnership for Research and Education in Materials (NSF DMR-2122128).