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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.

Optoelectronic properties of Au18(SR)14 are modulated by Ag doping, and its influence on photoelectrochemical performance is investigated. The best compromise for light conversion efficiency is made when a single Ag atom is incorporated.

Sensitive and selective detection of nitric oxide (NO) in the human body is crucial since it has the vital roles in the physiological and pathological processes. This study reports a new type of electrochemical NO biosensor based on zinc-dithiooxamide framework derived porous ZnO nanoparticles and polyterthiophene-rGO composite. By taking advantage of the synergetic effect between ZnO and poly(TTBA-rGO) (TTBA = 3'-(p-benzoic acid)-2,2':5',2″-terthiophene, rGO = reduced graphene oxide) nanocomposite layer, the poly(TTBA-rGO)/ZnO sensor probe displays excellent electrocatalytic activity and explores to detect NO released from normal and cancer cell lines. The ZnO is immobilized on a composite layer of poly(TTBA-rGO). The highly porous ZnO offers a high electrolyte accessible surface area and high ion-electron transport rates that efficiently catalyze the NO reduction reaction. Amperometry with the modified electrode displays highly sensitive response and wide dynamic range of 0.019-76 × 10 m with the detection limit of 7.7 ± 0.43 × 10 m. The sensor probe is demonstrated to detect NO released from living cells by drug stimulation. The proposed sensor provides a powerful platform for the low detection limit that is feasible for real-time analysis of NO in a biological system.

Ultrasmall gold nanoclusters (Au NCs) have recently gained enormous popularity as a newly emerging light harvester, but many fundamental aspects of their photoelectrochemical behavior are still largely unknown. Unlike traditional photoactive nanoparticles, the NC's core structure, rather than its size, is a key factor that dictates the physical properties of NCs because of a strong quantum confinement effect. Despite this importance, no effort has been made to elucidate the effect of the core structure on the photoelectrochemistry of Au NC-sensitized TiO 2 (Au NC−TiO 2 ). Using Au 25 NC as a model system, we delicately tailored the icosahedral Au 13 core of Au 25 NC into a cuboctahedral Au 15 core of Au 23 NC. This subtle core manipulation has a drastic impact on the entire interfacial behavior of Au NC−TiO 2 , which in turn significantly affects the photoelectrochemical performance. This new insight highlights the overlooked effect of the core structure on the photoelectrochemistry of Au NC−TiO 2 .