Ruthenium-based electrocatalysts for oxygen reduction reaction—a review

Innovative InAg-carbon nanocomposites: mesoporous design for OER enhancement

To produce clean and sustainable hydrogen energy through water electrolysis, the sluggish oxygen evolution reaction (OER) needs to be accelerated sustainably by using stable and highly effective electrocatalysts. Bimetallic nanocomposites have been recently recognized as an interesting class of electrocatalysts because of their synergistic behaviour, tunable morphology, and high catalytic efficiency. Herein, InC, AgC, and InAgC nanocomposites were synthesised via a hydrothermal method using a mesoporous carbon support derived from the carbonisation of giant cane. The structural characterisation revealed that the InC composite has tetragonal In with a minor presence of cubic In2O3, whereas AgC and InAgC are well aligned with cubic Ag and tetragonal In. Electron microscopy revealed that InC has a 3D plate-like structure, while InAgC exhibits a spherical shape and is uniformly dispersed across the carbon surface. InAgC showed excellent activity and durability for the OER, with a notably low overpotential of 480 mV at a current density of 100 mA cm-2, a Tafel slope of 97 mV dec-1, and an oxygen production turnover frequency of 10.19 s-1. The chronoamperometric (i-t) study of InAgC at 1.58 V vs. RHE for 20 h in 1 M KOH indicates that the catalyst is highly stable for the OER in alkaline electrolytes. The electrochemical double-layer capacitance (Cdl) value in the non-faradaic potential region of InAgC is greater (52.14 mF cm-2) than those of mesoporous carbon (16.54 mF cm-2), AgC (33.10 mF cm-2), and InC (48.77 mF cm-2), which is attributed to InAgC having more accessible active sites for the OER. This work presents numerous possibilities for developing effective nanocomposites using giant cane as a natural carbon source.

Dispersion and stability mechanism of Pt nanoparticles on transition-metal oxides

The heterogeneous catalysts of Pt/transition-metal oxides are typically synthesized through calcination at 500 °C, and Pt nanoparticles are uniformly and highly dispersed when hydrogen peroxide (H₂O₂) is applied before calcination. The influence of H₂O₂ on the dispersion and the stability of Pt nanoparticles on titania-incorporated fumed silica (Pt/Ti-FS) supports was examined using X-ray absorption fine structure (XAFS) measurements at the Pt L₃ and Ti K edges as well as density functional theory (DFT) calculations. The local structural and chemical properties around Pt and Ti atoms of Pt/Ti-FS with and without H₂O₂ treatment were monitored using in-situ XAFS during heating from room temperature to 500 °C. XAFS revealed that the Pt nanoparticles of H₂O₂-Pt/Ti-FS are highly stable and that the Ti atoms of H₂O₂-Pt/Ti-FS support form into a distorted-anatase TiO₂. DFT calculations showed that Pt atoms bond more stably to oxidized-TiO₂ surfaces than they do to bare- and reduced-TiO₂ surfaces. XAFS measurements and DFT calculations clarified that the presence of extra oxygen atoms due to the H₂O₂ treatment plays a critical role in the strong bonding of Pt atoms to TiO₂ surfaces.

A CoNi telluride heterostructure supported on Ni foam as an efficient electrocatalyst for the oxygen evolution reaction

The excellent oxygen evolution reaction performance of a CoNi telluride heterostructure (0.4CoNi LDH@Te-180C) can be attributed to the inherent layered structure, interconnected nanoarray structures and the synergistic effect of Co and Ni species.

Pt-Free Metal Nanocatalysts for the Oxygen Reduction Reaction Combining Experiment and Theory: An Overview

The design and manufacture of highly efficient nanocatalysts for the oxygen reduction reaction (ORR) is key to achieve the massive use of proton exchange membrane fuel cells. Up to date, Pt nanocatalysts are widely used for the ORR, but they have various disadvantages such as high cost, limited activity and partial stability. Therefore, different strategies have been implemented to eliminate or reduce the use of Pt in the nanocatalysts for the ORR. Among these, Pt-free metal nanocatalysts have received considerable relevance due to their good catalytic activity and slightly lower cost with respect to Pt. Consequently, nowadays, there are outstanding advances in the design of novel Pt-free metal nanocatalysts for the ORR. In this direction, combining experimental findings and theoretical insights is a low-cost methodology—in terms of both computational cost and laboratory resources—for the design of Pt-free metal nanocatalysts for the ORR in acid media. Therefore, coupled experimental and theoretical investigations are revised and discussed in detail in this review article.

Structural, electrochemical and photophysical behavior of Ru(ii) complexes with large bite angle sulfur-bridged terpyridyl ligands

Sulfur-bridged terpyridyl ligands expand the bite angles in Ru(ii) species leading to geometries very close to that of a “perfect” octahedron. Altering the donor strength of substituents results in systematic tuning of the redox properties.

Nitrogen-enriched carbon from melamine resins with superior oxygen reduction reaction activity

Catalytic carbon: Nitrogen-doped porous carbon (CN(x)) electrocatalysts are derived from inexpensive melamine formaldehyde resins. These potential PEMFC catalysts are synthesized by using a facile method, which yields materials that contain a meso- and macroporous structure. The carbon-based materials display attractive catalytic activity toward ORR and superior stability compared to a commercial Pt-based catalyst.

A nitrogen-doped polyaniline carbon with high electrocatalytic activity and stability for the oxygen reduction reaction in fuel cells

PANI-BASED CARBON CAT: A low-cost nitrogen-doped carbon nanomaterial from polyaniline as fuel cell cathode electrocatalyst is prepared by chemical polymerization of aniline monomers, followed by pyrolysis in the presence of ammonia. The catalyst demonstrates high activity, with an onset potential comparable to, and a reduction current higher than, a commercial platinum catalyst.

Electrodeposition of multilayered bimetallic nanoclusters of ruthenium and platinum via surface-limited redox-replacement reactions for electrocatalytic applications

An electrochemical synthesis of multilayered bimetallic Ru|Pt nanoclusters, supported on glassy carbon, is reported for the first time. The novel nanoclusters were synthesized via surface-limited redox-replacement reactions involving sacrificial Cu, deposited prior to the formation of each individual noble metal layer, in a sequential fashion. It has been shown that the Cu adlayers control the morphology and electrochemical properties of the resultant nanostructures. Sequentially deposited Ru|Pt nanoclusters exhibited superior electrocatalytic activity (when compared to equivalent monometallic Pt and an alloy-type codeposited Pt-Ru nanostructures) with respect to methanol electrooxidation in an acidic medium. Moreover, it has been established that the electrochemical process taking place at the Ru|Pt nanoclusters followed the bifunctional mechanism. Electrokinetic studies of the oxygen reduction reaction (ORR) were also performed. Analysis of hydrodynamic linear sweep voltammetric experiments, performed at various flow rates on oxygen-saturated acidic medium, revealed that the Pt and Ru|Pt nanoclusters exhibited direct four- and two-electron ORR pathways, respectively. A specially designed electrochemical flow-cell was used for automated sequential electrodeposition of the multilayered nanoclusters of predefined composition and electrochemical and electrocatalytic investigations.