Controlling Photoinduced H2 Release from Freestanding Borophane Sheets Under UV Irradiation by Tuning B–H Bonds

Abstract Hydrogen boride (HB), a freestanding 2D hydrogenated‐borophene (borophane) polymorph, is synthesized via ion exchange. HB sheets with a B/H atomic ratio of 1.0 are confirmed to contain three‐center–two‐electron B–H–B bonds and two‐center–two‐electron terminal B–H bonds. The optical properties of HB sheets are expected to be tunable by changing the BHB/BH bond ratio, which alters the electronic structure of HB sheets; however, this is not yet achieved. This study demonstrates that controlling the BHB/BH bond ratio in the HB sheets is possible without altering the hydrogen content by adjusting the volume of ion‐exchange resin during synthesis, thus enabling the tuning of the photoinduced H2 release under UV irradiation. Furthermore, the fluorescence intensity correlates with the absorbance ratio of the BHB and BH vibrational modes. Increasing the BHB/BH bond ratio enhances the luminescence intensity, whereas reducing it enhances the photoinduced H2 release rate under UV irradiation. The ability to control the BHB/BH bond ratio of HB sheets provides new avenues for optimizing their properties for various applications, including hydrogen storage and photocatalysis.