Hydrogel is used as a structural template and precursor to prepare carbon aerogel doped with Fe–Co bimetal sites as bifunctional catalysts for ORR and OER, which exhibits enhanced activity and stability, as compared to the monometal counterparts.

Design and engineering of bifunctional catalysts are critical in the development of electrochemical full water splitting. In this study, 4-ethylphenylacetylene-functionalized iridium (Ir− C, 1.7 ± 0.3 nm in diameter) nanoparticles are found to exhibit markedly enhanced electrocatalytic activity toward both hydrogen and oxygen evolution reactions (HER and OER) in acidic and alkaline media, in comparison to the nanoparticles capped with mercapto and nitrene derivatives. Remarkably, the HER and OER performances in alkaline media are even better than those of commercial Ir/C and Pt/C benchmarks. This is accounted for by the formation of Ir−CC− conjugated interfacial linkage that leads to significant intraparticle charge delocalization and hence manipulation of the electron density of the Ir nanoparticles and interactions with key reaction intermediates. This is indeed confirmed by results from both spectroscopic measurements and density functional theory calculations. With Ir−C nanoparticles as both the cathode and anode catalysts for electrochemical water splitting, a low cell voltage of 1.495 and 1.473 V is needed to reach the current density of 10 mA cm −2 in alkaline and acidic media, respectively. Such a performance is markedly better than that of commercial Ir/C (1.548 and 1.561 V) and relevant catalysts reported in recent literature, highlighting the significance of interfacial engineering in the development of high-performance bifunctional electrocatalysts.

Metal–nitrogen–carbon (MNC) nanocomposites have been hailed as promising and efficient electrocatalysts toward oxygen reduction reaction (ORR), due to the formation of MN x coordination moieties. However, MNC hybrids are mostly prepared by pyrolysis of organic precursors along with select metal salts, where part of the MN x sites are inevitably buried in the carbon matrix. This limited accessibility compromises the electrocatalytic performance. Herein, we describe a wet-impregnation procedure by facile thermal refluxing, whereby palladium is atomically dispersed and enriched onto the surface of hollow, nitrogen-doped carbon cages (HNC) forming Pd–N coordination bonds. The obtained Pd-HNC nanocomposites exhibit an ORR activity in alkaline media markedly higher than that of metallic Pd nanoparticles, and the best sample even outperforms commercial Pt/C and relevant Pd-based catalysts reported in the literature. The results suggest that atomic dispersion and surface enrichment of palladium in a carbon matrix may serve as an effective strategy in the fabrication of high-performance ORR electrocatalysts.

This study reports the preparation, characterization, and electrocatalytic properties of palladium-based catalysts containing ceria (CeO 2 ) on carbon black (CB) and onion-like carbon (OLC) supports. The electrocatalysts (Pd− CeO 2 /CB and Pd−CeO 2 /OLC) exhibit a large specific surface area, pore volume, and small particle size, as well as enhanced interfacial interaction and synergy among Pd, CeO 2 , and OLC in Pd−CeO 2 /OLC that are valuable for improved electrocatalysis. The presence of CeO 2 in Pd−CeO 2 /OLC induces ca. 7% defects and modifies the electronic structure of the Pd/OLC interface, significantly improving the electrical conductivity due to enhanced charge redistribution, corroborated by density functional theory (DFT) calculations. Pd−CeO 2 /OLC displays the lowest adsorption energies (H*, OH*, and OOH*) among the series. For the hydrogen oxidation reaction (HOR), Pd−CeO 2 /OLC delivers significantly enhanced HOR (mass-specific) activities of 4.2 (8.1), 13.2 (29.6), and 15 (78.5) times more than Pd−CeO 2 /CB, Pd/OLC, and Pd/CB, respectively, with the best diffusion coefficient (D) and heterogeneous rate constant (k). Pd−CeO 2 /OLC also displays less degradation during accelerated durability testing. In an anion-exchange-membrane fuel cell (AEMFC) with H 2 fuel, Pd−CeO 2 /OLC achieved the highest peak power density of 1.0 W cm −2 at 3.0 A cm −2 as compared to Pd−CeO 2 /CB (0.9 W cm −2 at 2.2 A cm −2 ), Pd/OLC (0.6 W cm −2 at 1.7 A cm −2 ), and Pd/CB (0.05 W cm −2 at 0.1 A cm −2 ). These results indicate that Pd−CeO 2 /OLC promises to serve as a high-performing and durable anode material for AEMFCs.

The design and engineering of graphene-based nanomaterials for antimicrobial applications is attracting extensive interest. Here, we highlight the differential toxicity and phototoxicity of graphene oxide quantum dots after NaBH4 reduction.

Oxygen reduction reaction (ORR) plays an important role in dictating the performance of various electrochemical energy technologies. As platinum nanoparticles have served as the catalysts of choice towards ORR, minimizing the cost of the catalysts by diminishing the platinum nanoparticle size has become a critical route to advancing the technological development. Herein, first-principle calculations show that carbon-supported Pt9 clusters represent the threshold domain size, and the ORR activity can be significantly improved by doping of adjacent cobalt atoms. This is confirmed experimentally, where platinum and cobalt are dispersed in nitrogen-doped carbon nanowires in varied forms, single atoms, few-atom clusters, and nanoparticles, depending on the initial feeds. The sample consisting primarily of Pt2~7 clusters doped with atomic Co species exhibits the best mass activity among the series, with a current density of 4.16 A mgPt−1 at +0.85 V vs. RHE that is almost 50 times higher than that of commercial Pt/C.

Antibiotic resistance is an imminent threat to human health, requiring the development of effective alternate antibacterial agents. One such alternative includes nanoparticle (photo)­catalysts that are good at producing reactive oxygen species (ROS). Herein, we report the design and preparation of nitrogen-doped carbon dots functionalized with atomically dispersed copper centers by Cu–N coordination (Cu/NCD) that exhibit apparent antibacterial activity toward Gram-negative Escherichia coli (E. coli) under photoirradiation. The growth of E. coli cells is found to be markedly inhibited by Cu/NCD under 365 nm photoirradiation, whereas no apparent inhibition is observed in the dark or with the copper-free carbon dots alone. This is ascribed to the prolonged photoluminescence lifetime of Cu/NCD that facilitates the separation of photogenerated electron–hole pairs and ROS formation. The addition of tert-butyl alcohol is found to completely diminish the antimicrobial activity, suggesting that hydroxyl radicals are responsible for microbial death. Consistent results are obtained from fluorescence microscopic studies using CellROX green as the probe. Similar bactericidal behaviors are observed with Gram-positive Staphylococcus epidermidis (S. epidermidis). The copper content within the carbon material is optimized at a low loading of 1.09 wt %, reducing the possibility of toxic copper-ion leaching. Results from this study highlight the significance of carbon-based nanocomposites with isolated metal species as potent antimicrobial reagents.

The design and engineering of high-performance antimicrobial agents is critical for combating antibiotic resistance. In the present study, a rapid and broad-spectrum bactericidal agent is developed based on nanocomposites consisting of cobalt-doped zinc oxide (CoZnO) nanoparticles and MoS 2 nanosheets. The CoZnO/MoS 2 nanocomposites are prepared by a facile chemical precipitation method at controlled CoZnO and MoS 2 feeds. Scanning and transmission electron microscopic measurements show that CoZnO nanoparticles (ca. 10 nm in diameter) are clustered on the MoS 2 nanosheet surface, which facilitates the charge separation of the photo-generated electron−hole pairs, leading to enhanced photodynamic antimicrobial activity. Antibacterial assays in the dark show that the CoZnO/MoS 2 nanocomposite prepared at 30 μg of MoS 2 feed (CoZnO/MoS 2 -30) exhibits the best performance among a series of samples, with minimum inhibitory concentrations of 0.25, 0.8, and 1.8 mg mL −1 toward the Gram-negative bacterium Escherichia coli, Grampositive bacterium Staphylococcus aureus and fungus Aspergillus flavus, respectively. The antibacterial performance is markedly enhanced under photoirradiation, where 94.0% inactivation of E. coli is achieved with 20 μg mL −1 CoZnO/MoS 2 -30 nanocomposite under photoirradiation (15 W, 360 nm) for 5 min. The high antibacterial activity can be ascribed to peroxidase-like photocatalytic activity that is conducive to the generation of reactive oxygen species, as evidenced in transmission electron microscopy, electron spin resonance, and intracellular glutathione oxidation measurements. The results of the present study highlight the significance of CoZnO/MoS 2 nanocomposites as potent photodynamic antibacterial agents.