Size and Electronic Modulation of Iridium Nanoparticles on Nitrogen-Functionalized Carbon toward Advanced Electrocatalysts for Alkaline Water Splitting

Electron flux at the Schottky junction of Bi NPs and WO3-supported g-C3N4: an efficient ternary S-scheme catalyst for removal of fluoroquinolone-type antibiotics from water

Recently, global-scale attempts have been conducted to develop clean technologies and affordable materials to remediate pharmaceutical contaminants of water resources that are resistant to the biodegradation. In line with global efforts, this study reports a facile method to fabricate Bi nanocrystals in situ decorated on WO₃ nanoplates and its composite with graphitic carbon nitride (WO₃/Bi/g-C₃N₄) for photocatalytic degradation of fluoroquinolone-type antibiotics (ciprofloxacin and ofloxacin). The designed ternary S-scheme WO₃/Bi/g-C₃N₄ composite material was fully characterized by physicochemical and electrochemical analysis. Depositing the cost-effective and earth-abundant Bi nanocrystals onto WO₃ via a facile reduction route has been shown to increase the boosting of electron flux at their interface (Schottky junction). The S-scheme separation is confirmed by the calculation of band positions and the analysis of photogenerated hydroxyl radicals and holes. The complete removal of contaminants was obtained over the WO₃/Bi/g-C₃N₄ photocatalyst after 90 min under visible light irradiation. The present work would provide a rational route for developing Bi NP-based photocatalysis to replace metallic Au, Pt, and Ag NPs.

Enhanced stability of sub-nanometric iridium decorated graphitic carbon nitride for H2 production upon hydrous hydrazine decomposition

Stabilizing metal nanoparticles is vital for large scale implementations of supported metal catalysts, particularly for a sustainable transition to clean energy, e.g., H₂ production. In this work, iridium sub-nanometric particles were deposited on commercial graphite and on graphitic carbon nitride by a wet impregnation method to investigate the metal-support interaction during the hydrous hydrazine decomposition reaction. To establish a structure-activity relationship, samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic performance of the synthesized materials was evaluated under mild reaction conditions, i.e. 323 K and ambient pressure. The results showed that graphitic carbon nitride (GCN) enhances the stability of Ir nanoparticles compared to graphite, while maintaining remarkable activity and selectivity. Simulation techniques including Genetic Algorithm geometry screening and electronic structure analyses were employed to provide a valuable atomic level understanding of the metal-support interactions. N anchoring sites of GCN were found to minimise the thermodynamic driving force of coalescence, thus improving the catalyst stability, as well as to lead charge redistributions in the cluster improving the resistance to poisoning by decomposition intermediates.

Dependence of Precursor Graphite Flake Size on Nitrogen Doping in Graphene Oxide and Its Effect on OER Catalytic Activity

We report the synthesis of nitrogen-doped graphene oxide, with 5.7-7.0 wt % nitrogen doping, from different sizes of precursor graphite and study its effect on the oxygen evolution reaction (OER) activity of IrO₂ in an acidic medium. The nitrogen-doped supports are expected to have pyridinic, pyrrolic, and graphitic functionalities at different ratios responsible for their improved performance. The N-doped supports and catalysts are synthesized via pyrolysis and the hydrothermal method using natural and synthetic graphite of three different flake sizes and evaluated for their structural and electrochemical characteristics. The average size of IrO₂ nanoparticles deposited on the N-doped supports is independent of the flake size and doping amount of nitrogen. The catalysts show optimum current densities but improved stability with increasing flake sizes of 7, 20, and 125 μm. Our results demonstrate that the selection of the flake size of the doped support is necessary to achieve durable catalysts for the OER in an acidic medium.

Ir nanoclusters/porous N-doped carbon as a bifunctional electrocatalyst for hydrogen evolution and hydrazine oxidation reactions

One common iridium(III) complex was employed to facilely prepare ultrafine Ir nanoclusters embedded in porous N-doped carbon, which displayed significant bifunctional activity for both hydrogen evolution and hydrazine oxidation under alkaline conditions, enabling energy-efficient hydrogen production.

Formation and selected catalytic properties of ruthenium, rhodium, osmium and iridium nanoparticles

The synthesis and applications in catalysis of nanoparticles formed from ruthenium, rhodium, osmium and iridium have been reviewed.

Ir-based bifunctional electrocatalysts for overall water splitting

The recent progress on Ir-based bifunctional electrocatalysts in enhancing the overall water splitting performance is reviewed mainly from the aspects of optimizing the composition and morphology.

Surface Engineering on Nickel-Ruthenium Nanoalloys Attached Defective Carbon Sites as Superior Bifunctional Electrocatalysts for Overall Water Splitting

Herein, we report a novel catalyst of nickel-ruthenium alloy nanoparticles (NPs) homogeneously enriched in the wall of multiwalled carbon nanotubes (denoted as NiRu@MWCNTs) via a facile plasma reduction method. The NiRu@MWCNTs exhibits remarkable electrocatalytic activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The required overpotentials to drive a current density of 10 mA cm^-2 (η₁₀) over NiRu@MWCNTs are only 14 and 240 mV, corresponding to Tafel slopes of 32 and 55 mV dec^-1 for the HER and OER in alkaline medium, respectively. Furthermore, the NiRu@MWCNTs electrolyzer shows low η₁₀ of 330, 380, and 280 mV in acidic, neutral, and alkaline media, respectively. Density functional theory (DFT) calculations and experimental results reveal that the NiRu alloy NPs attached to the defective and nondefective carbon are the key active sites for the HER and OER, respectively, thus resulting in superior isolated synergistic bifunctional active sites for overall water splitting. Our work provides a promising strategy for efficient synthesis of robust catalysts with specific bifunctional active sites for overall water splitting in a wide pH range, along with deep insight into the catalytic mechanism.

Spontaneous deposition of Ir nanoparticles on 2D siloxene as a high-performance HER electrocatalyst with ultra-low Ir loading

Based on the reducibility of siloxene, Ir nanoparticles were spontaneously deposited on siloxene and showed excellent performance for the HER.

Electrochemical performance of ruthenium nanoparticles decorated on nitride carbon for non-enzymatic detection of hydrogen peroxide

Development of high-performance Pt-free non-enzymatic hydrogen peroxide (H2O2) sensors on the basis of supported metal nanoparticles (NPs) is important for industrial and biological applications. Here, we report the preparation of ultrafine, surface-clean, and well-distributed Ru NPs and concomitant formation of nitride carbon (Ru/NC) by pyrolyzing tris(2,2'-bipyridyl)ruthenium(ii) chloride (TBRC) with carbon. The use of the nitrogen (N)-containing Ru complex of TBRC as the metal precursor is essential for the preparation of ultrafine and highly dispersed Ru NPs (1.20 nm in diameter) on a NC support. The as-synthesized Ru/NC-800 displays superior analytical performance for non-enzymatic detection of H2O2 with a low detection limit of 0.468 μM, high sensitivity of 698 μA mM-1 cm-2, excellent linear detection ranging from 0.001 to 10.000 mM, good stability, and high selectivity. The control experiment results indicate that the high-performance of Ru/NC-800 must be ascribed to the ultrasmall and highly dispersed Ru NPs and N-doping, which can supply a higher density of active sites available for H2O2 detection. This study provides a facile strategy to synthesize ultrafine metal NPs and for concomitant production of NC for electrocatalytic non-enzymatic sensing.

Ultrafine and monodispersed iridium nanoparticles supported on nitrogen-functionalized carbon: an efficient oxidase mimic for glutathione colorimetric detection

Ultrafine and monodispersed Ir NPs supported on nitrogen-functionalized carbon served as an efficient oxidase mimic for glutathione colorimetric detection.

Towards High-Efficiency Hydrogen Production through in situ Formation of Well-Dispersed Rhodium Nanoclusters

Rh-based materials have emerged as potential candidates for hydrogen revolution from electrolyzing water or ammonia borane (AB) hydrolysis. Nevertheless, most of the catalysts still suffer from the complex synthetic procedures combined with limited catalytic activity. Additionally, the facile syntheses of Rh catalysts with high efficiencies for both electrochemical water splitting and AB hydrolysis are still challenging. Herein, we develop a simple, green, and mass-producible ion-adsorption strategy to produce a Rh/C pre-catalyst (pre-Rh/C). The ultrafine and clean Rh nanoclusters immobilized on carbon are achieved via the in situ reduction of the pre-Rh/C during the hydrogen-evolution process. The resulting in situ Rh/C catalyst presents an outstanding electrocatalytic performance with low overpotentials of 8 and 30 mV at 10 mA cm^-2 in 1.0 m KOH and 0.5 m H₂ SO₄ , respectively, outperforming the state-of-the-art Pt catalysts. Furthermore, the in situ Rh/C is also highly active for AB hydrolysis to produce hydrogen with a high turnover frequency of 1246 mol H2  mol_Rh^-1  min^-1 at 25 °C. The in situ-formed ultrafine Rh nanoclusters are responsible for the observed superior catalytic performance. This facile in situ strategy to realize a highly active catalyst shows promise for practical applications.