Similar Looks, Different Photoelectrochemical Behavior: Unique Aspects of Metal-Nanocluster-Sensitized Electrodes

Abstract

Metal nanoclusters (NCs) were initially used in light-harvesting applications as mere alternatives to traditional photosensitizers; therefore, NCs are often evaluated using a similar set of parameters as those developed for their traditional counterparts. Despite the resemblance in the design architectures and working principles of NC-based and traditional-sensitized photoelectrodes, recent studies have revealed that the photoelectrochemical (PEC) attributes of NC-sensitized photoelectrodes are distinctly different. Therefore, it is important to redefine the criteria used for assessing NCs in energy conversion devices. In this Focus Review, we present a comprehensive overview of some unique PEC behavior of NC-sensitized photoelectrodes. We also provide a mechanistic description of the photodegradation route and how it can be manipulated to compensate for photosensitization loss in NCs under practical operating conditions. Finally, we discuss future research directions to achieve a better understanding of the unique PEC behavior that will help to establish new design principles.

Understanding the Photoelectrochemical Behavior of Metal Nanoclusters: A Perspective

“…However, research has shown that NCs should not be treated merely as a separate class of sensitizers because they possess various attributes and mechanisms unseen in other sensi- tizers. 41 This misconception was also made with perovskite devices. Early research used perovskite merely as a sensitizer and even utilized liquid redox couples as electrolytes.…”

“…Hence, ligands also play a crucial role in successfully utilizing NCs in PEC applications. This is the reason why almost all publications on NC utilization in PEC applications make use of GSH-protected NCs. ,,,, This is mainly because of their exceptional photochemical stability and long excited-state lifetimes . While the GSH-protected Au NCs display good stability in corrosive I – /I 3 – redox environments, GSH-protected Ag NCs decompose readily, even in mild Co 2+ /Co 3+ redox environments (Figure C). ,, Iodide is very corrosive to gold.…”

Metal nanocluster‐based devices: Challenges and opportunities

“…[ 41 ] Possessing molecule‐like properties, metal NCs were found to be able to capture and converse incident photons to electricity. [ 102,107 ] Kamat group reported MCSCs using Au:SG NCs as sensitizers. [ 36 ] The as‐prepared NCs exhibited orange emission with a maximum at 600 nm, indicating excited‐state deactivation of these NCs through a radiative route.…”

Influence of the Electronic Properties of the Ligand on the Photoelectrochemical Behavior of Au25 Nanocluster-Sensitized TiO2 Photoanode

“…The excited state of a body-centered-cubic Au 38 cluster was reported to have a lifetime of ∼5 μs, which is comparable to that of bulk silicon . All of this endows metal NCs good photocatalytic activity and makes them promising material in light energy conversion. − For example, glutathione (GSH) protected Au x -SG NCs have been extensively used in photovoltaic and photoelectrochemical (PEC) systems. − Among Au 10 , Au 15 , Au 18 , and Au 25 , Au 18 was proposed as the best photosensitizer in metal-cluster-sensitized solar cells (MCSSCs). − By doping single Ag atom into Au 18 , a power conversion efficiency of 4.22% was achieved . The advantage of Au x -SG is the ease of synthesis .…”