Efficient H2O2 Synthesis Through a Two-Electron Oxygen Reduction Reaction by Electrocatalysts

The two-electron oxygen reduction reaction (2e-ORR) for the sustainable synthesis of hydrogen peroxide (H2O2) has demonstrated considerable potential for local production of this environmentally friendly chemical oxidant on small, medium, and large scales. This method offers a promising alternative to the energy-intensive anthraquinone approach, placing a primary emphasis on the development of efficient electrocatalysts. Improving the efficiency of electrocatalysts and uncovering their catalytic mechanisms are essential steps in achieving high 2e-ORR activity, selectivity, and stability. This comprehensive review summarizes recent advancements in electrocatalysts for in-situ H2O2 production, providing a detailed overview of the field. In particular, the review delves into the design, fabrication, and investigation of catalytic active sites contributing to H2O2 selectivity. Additionally, it highlights a range of electrocatalysts including pure metals and alloys, transition metal compounds, single-atom catalysts, and carbon-based catalysts for the 2e-ORR pathway. Finally, the review addresses significant challenges and opportunities for efficient H2O2 electrosynthesis, as well as potential future research directions.

Origin of the superior oxygen reduction activity of zirconium nitride in alkaline media

The anion exchange membrane fuel cell (AEMFC), which can operate in alkaline media, paves a promising avenue for the broad application of earth-abundant element based catalysts. Recent pioneering studies found that zirconium nitride (ZrN) with low upfront capital cost can exhibit high activity, even surpassing that of Pt in alkaline oxygen reduction reaction (ORR). However, the origin of its superior ORR activity was not well understood. Herein, we propose a new theoretical framework to uncover the ORR mechanism of ZrN by integrating surface state analysis, electric field effect simulations, and pH-dependent microkinetic modelling. The ZrN surface was found to be covered by ∼1 monolayer (ML) HO* under ORR operating conditions, which can accommodate the adsorbates in a bridge-site configuration for the ORR. Electric field effect simulations demonstrate that O* adsorption on a 1 ML HO* covered surface only induces a consistently small dipole moment change, resulting in a moderate bonding strength that can account for the superior activity. Based on the identified surface state of ZrN and electric field simulations, pH-dependent microkinetic modelling found that ZrN reaches the Sabatier optimum of the kinetic ORR volcano model in alkaline media, with the simulated polarization curves being in excellent agreement with the experimental data of ZrN and Pt/C. Finally, we show that this theoretical framework can lead to a good explanation for the alkaline oxygen electrocatalysis of other transition metal nitrites such as Fe3N, TiN, and HfN. In summary, this study proposes a new framework to rationalize and design transition metal nitrides for alkaline ORR.

Spherical Silica Modified with Magnesium and Ruthenium-Synthesis, Characterization and Catalytic Properties

The design of different bimetallic catalysts is an important area of catalytic research in the context of their possible applications in the cascade processes, meeting the requirements of the so-called green chemistry. In this study, such catalysts were obtained by the incorporation of magnesium species into spherical silica, which was in the next step covered with porous silica and modified with ruthenium species. The structure and chemical composition of the materials obtained were determined by XRD measurements, low temperature N₂ adsorption/desorption, SEM, ICP-OES and XPS methods. The catalytic activities of materials obtained were tested in 2-propanol decomposition and hydrogenation of levulinic acid. The results obtained confirmed the successful coverage of nanospheres with porous silica. A much higher concentration of ruthenium species was found on the surface of the catalysts than in their bulk. The opposite relationship was observed for magnesium species. The modification of nanospheres with silica had a positive effect on the catalytic activity of the materials obtained. For the most active sample, i.e., Ru/NS/3Mg/NS, 49% of levulinic acid conversion in its hydrogenation process was reported with γ-valerolactone as the only product.

Regulating the Coordination of Co sites in Co3 O4 /MnO2 Compounding for Facilitated Oxygen Reduction Reaction

Binary transition metal oxides as a promising oxygen reduction reaction (ORR) catalyst have received significant attention. However, their exact reaction mechanisms are often too complex to be discussed. Herein, novel Co-Mn composites with a well-defined nanostructure were developed for understanding the role of each component. The growth pattern of cobalt oxide and the effects of the coordination environment of Co sites during growth on the overall activity were investigated. Based on experimental and density functional theory studies, it was found that the decaying coordination number directly affected the expression of crystal planes of cobalt oxide, which further had a great influence upon limiting current density of Co-Mn catalysts. The cuboid-Co/Mn catalyst exhibited outstanding limiting current density and showed good stability, related to more highly active (110) planes exposed in Co₃ O₄ . These provided many references for the preparation of related nonprecious catalysts in various domains.