Dual Role of Surface Hydroxyl Groups in the Photodynamics and Performance of NiO-Based Photocathodes

Abstract

Photoelectrochemical (PEC) cells containing photocathodes based on functionalized NiO show a promising solar-to-hydrogen conversion efficiency. Here, we present mechanistic understanding of the photoinduced charge transfer processes occurring at the photocathode/electrolyte interface. We demonstrate via advanced photophysical characterization that surface hydroxyl groups formed at the NiO/water interface not only promote photoinduced hole transfer from the dye into NiO, but also enhance the rate of charge recombination. Both processes are significantly slower when the photocathode is exposed to dry acetonitrile, while in air an intermediate behavior is observed. These data suggest that highly efficient devices can be developed by balancing the quantity of surface hydroxyl groups of NiO, and presumably of other p-type metal oxide semiconductors.

Interplay between Facets and Defects during the Dissociative and Molecular Adsorption of Water on Metal Oxide Surfaces

“…Hence, many chemical processesincluding adsorption, dissolution, and electron transferare determined by the atomic structure and interaction with water . Understanding the reactivity at this metal oxide–water interface begins with understanding how dry surfaces initially interact with water, typically resulting in the dissociation of some fraction of adsorbed water molecules to form a hydroxylated surface. − Because surface hydroxyl groups are known to act as anchor sites for solute binding, their arrangement and density influence a wide range of material properties, including foreign ion incorporation, toxic metal fate and transport, photodegradation of natural organic matter, and so forth. ,− Additionally, the type and distribution of surface hydroxyls strongly impacts the electronic structure of the material and hence plays a critical role in determining water oxidation performance in PEC devices. − …”

Photophysical Study on the Effect of the External Potential on NiO-Based Photocathodes

“…A likely reason for this contrast is a strong dependency of the NiO surface termination on the working environment. Considering the dual role of surface OHwe unraveled recently, accelerating both hole injection and charge recombination, 30 the dependency of the photodynamics on the external potential observed here is likely due to a change in ions (H + or OH -) in the IHP. The quantity of surface OHions is the highest at positive potential, resulting in both fast photoinduced hole injection and charge recombination.…”

Surface Modification of NiOx Layer with Versatile Coupling Agent Enables Enhanced Performance and Stability of Inverted Perovskite Solar Cells

“…[ 8 ] Furthermore, the device stability is adversely affected by high‐valence Ni ions and hydroxyl groups from the nanoparticles prepared by the sol–gel method. [ 9 ] In addition, the rough surface of NiO x layer also poses a serious challenge for the subsequent preparation of high‐quality perovskite layers. [ 10 ] To improve the performance of NiO x ‐based inverted PSCs, great efforts have been made on the preparation of NiO x layer and the optimization of perovskite/NiO x interface.…”