Digital-Twin Approach for Characterizing and Modeling Photocatalyst/Liquid Interfaces

Particulate photocatalysts, usually in a powder suspension or immobilized on a panel, host multiple concurring redox processes such as coevolving H₂ and O₂. The challenges of materials and interface characterizations lies in nanoscale proximity of reductive and oxidative sites, supported on photocatalyst surfaces. While co-evolving H₂ and O₂ is unsafe, instead, one can develop schemes of redox-mediated water splitting: H₂-evolving photocatalysts will produce hydrogen while selectively oxidizing, e.g., I^- to IO₃^- in solutions; a dichroic mirror splits the solar spectrum to allow O₂-evolving photocatalysts to absorb the solar light unused by the H₂-evolving photocatalysts; and the O₂-evolving catalysts produce oxygen while selectively reducing, e.g., IO₃^- back to I^- in a second solution.
In all cases, the conversion efficiency remain low. Instead of trial-and-error, we develop tools to probe the photocatalyst/liquid interfaces. In particular, we synthesized thin-film model photocatalysts by topographical transformation of nanoparticulate semiconductors into planar thin films, and we probe the front and back potentials of thin-film model photocatalysts using nanoscale scanning electrochemical potentiometry. Especially the challenge is to probe the deep hole charge potentials of O₂-evolvign photocatalysts having O 2p or N 2p levels at the valence band maximum. Using a novel hole-selective contact and open-circuit potential (OCP) measurements in O₂/redox mixtures as a characterization framework, we show that nanoscale photocatalyst-cocatalyst interfaces are critical if not more than the catalytic performance of . We employ x-ray photoemission spectroscopy for liquid interfaces to probe the local energetics. Thse kinetics and energetics characterizations establish a new digital/physical-twin approach to quantify and visualize the spatially distributed parameters that vary for 1 eV potential energy across nanoscale during photocatalyst operation. A systematic validation approach for the digital model will be discussed and analyzed.