Easily synthesizable, robust and earth abundant energy conversion materials can have an important contribution for a sustainable energy infrastructure. A recently discovered two dimensional carbon nitride called poly(heptazine imide) or PHI not only allows for efficient photocatalytic hydrogen evolution, but also enables intrinsic solar energy storage within the photoabsorber material for later use.^1,2 Wet processing of the organic and yet insoluble material offers pathways to modify the material’s structure and morphology, affecting its optoelectronic as well as ionic properties. We provide a holistic picture on how such interwoven parameter modifications influence the photocatalytic hydrogen evolution efficiency and delineate guidelines for optimized structure-property-activity relationships.^3-5

Photocatalysis can besides be used to propel microrobots. We show how appropriate processing of the multifunctional PHI material enables versatile applications as light driven microswimmers, which can be photocharged, navigated in biological media and act as drug delivery shuttles.^6,7 Stable PHI nanoparticle suspensions can further be used to form tailored photoelectrodes. Making use of PHI’s intrinsic light energy storage ability, we describe how they can be used to realize solar batteries, and how PHI can act as conceptually novel photomemristive sensor platform.^2,8,9

¹ H. Schlomberg, J. Kröger, G. Savasci et al., Chem. Mater. 31, 18, 7478–7486 (2019).

² F. Podjaski, J. Kröger, B. V. Lotsch, Adv. Mater. 30, 1705477 (2018).

³ J. Kröger, A. Jiménez-Solano, G. Savasci et al., Adv. Funct. Mater. 31, 2102468 (2021).

⁴ T. Banerjee, F Podjaski, J. Kröger et al., Nat. Rev. Mater. 6, 168–190 (2021).

⁵ J. Kröger, F. Podjaski, G. Savasci et al., Adv. Mater. 34, 2107061 (2022).

⁶ V. Sridhar, F. Podjaski, J. Kröger et al., Proc. Natl. Acad. Sci. U.S.A. 117, 24748–24756 (2020).

⁷ V. Sridhar, F. Podjaski, Y. Alapan et al., Sci. Rob. 7, eabm1421 (2022).

⁸ F. Podjaski, B.V. Lotsch, Adv. Energy Mater. 11, 202003049 (2021).

⁹ A Gouder, A. Jimenez-Solano, N. M. Vargas-Barbosa et al., submitted. arXiv:2109.06964