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Investigating photoelectrode interfaces is challenging due to complex charge carrier pathways, and photodegradation aggravates this difficulty because interfacial properties are significantly altered by degradation. Unlike dyes and semiconductors that degrade into photoinactive materials, the photodegradation of Au nanoclusters (NCs) yields Au nanoparticles (NPs) that are photoactive. Besides, these NPs can form Schottky barriers with TiO2, which can affect interfacial band structures. Hence, the copresence of this photoactive nanoduo gives rise to unprecedented complexity in understanding the photoelectrochemical behavior of NC-sensitized photoelectrodes. In this work, we unveil that electron injection into TiO2 and subsequent electron trapping at deep surface trap states in TiO2, which are created by sensitization, play a vital role in the photodegradation. We also demonstrate that photocurrent can be enhanced through judicious control over photodegradation that would otherwise be deleterious. This photocurrent enhancement is attributed to multiple overlooked effects of Au NPs (plasmonic field enhancement and interfacial band bending).

Recently, gold nanoclusters (Au NCs) have become more popular as their structure–property relationships start to rival those of conventional Au NPs. The molecular-type energy transition and quantum confinement effects of Au NCs are fundamentally different from those of Au NPs. Because of these intriguing features, Au NCs are gaining special attention in catalysis research and are being used as model catalysts to understand catalytic properties and structures at the atomic level. Although catalysis research is a longstanding discipline, the fundamental insights into structure–property relationships at the atomic level, such as reaction mechanism/activation at the catalyst surface and identification of actives sites, remain largely unexplored. Atomically precise Au NCs can provide access to such information because of their exact molecular information, monodisperse nature, molecule-like properties, and well-resolved atomic structure from X-ray crystallography, akin to protein structures in enzyme-based catalysis. This accurate data also provides essential information for computational investigations. In this Perspective, we summarize the recent progress made using Au NCs as electrocatalytic materials for oxygen reduction, water electrocatalysis, and electrochemical reduction of carbon dioxide, and we discuss challenges to overcome existing limitations. We hope that our Perspective motivates more researchers to investigate different aspects of Au NCs toward a better understanding of the structure–performance correlations in catalysis.

Dealloyed‐AuNi dendrite anchored on carboxylic acid groups of a conducting polymer is prepared and demonstrated for the catalysis of the oxygen reduction reaction (ORR) and detection of hydrogen peroxide (H2O2) released from living cells. The dendrite formation is initiated on a poly(benzoic acid‐2,2′:5′,2′′‐terthiophene) (pTBA) layer, where the polymer layer acts as a stable substrate to improve the long‐term stability and catalytic activity of the alloy electrode. A co‐deposition of Au and Ni is performed to produce a Ni‐rich Au surface at first; subsequent removal of the surface Ni atoms through electrochemical dealloying enhances the performance of the catalyst because of an increase in the electrochemically active area by 12 times. The hydrodynamic voltammetry of dealloyed‐AuNi@pTBA shows a half‐wave potential at –0.08 V, which is a large shift towards more positive potential when compared to those on AuNi@pTBA (−0.14 V) and commercial Pt/C (–0.12 V) electrodes. The proposed catalytic electrode achieved a superior analytical performance for the detection of trace H2O2 (at –0.15 V) released from cancer and normal cells with a very low detection limit (ca. 5 nM). In addition, the in vitro studies suggest no significant cytotoxicity effect for the dealloyed sample and the viability of the cells are more than 85% even after 48 h of incubation.