Computational Simulations on the Oxygen Reduction Reaction in Electrochemical Systems

Mechanism for the Direct Synthesis of H2O2 on Pd Clusters: Heterolytic Reaction Pathways at the Liquid–Solid Interface

“…In contrast to the previously proposed Langmuir–Hinshelwood mechanisms, ,, the findings of this work implicate a proton–electron transfer mechanism (Scheme , steps 4 and 5) as the primary pathway for H 2 O 2 formation. Notably, this mechanism resembles proposals for the two-electron ORR to H 2 O 2 , , however, without an applied electrical potential. Instead, the catalytic direct synthesis of H 2 O 2 on silica-supported Pd clusters is driven by the chemical potential of the supplied H 2 (g).…”

“…The proposed mechanism for H 2 O 2 formation (Schemes and ) contains steps identical to charge-transfer processes for the ORR. , These steps are well-accepted when an electrical potential is applied between two metal electrodes separated by an electrolyte; however, they are not commonly invoked to describe reactions at the surface of nanoclusters supported on insulators (e.g., Pd–SiO 2 ). Figure shows that increases in the H 2 O 2 concentration over time within a semibatch reactor are much greater in protic solvents (e.g., methanol and water) than in aprotic solvents (e.g., acetonitrile, dimethyl sulfoxide, and propylene carbonate) (4.2 kPa H 2 , 4.2 kPa O 2 , 295 K, 3.8 wt % Pd–SiO 2 ).…”

Direct Synthesis of H2O2 from H2 and O2 on Pd Catalysts: Current Understanding, Outstanding Questions, and Research Needs

“…Therefore, we must carefully consider the meaning of predictions derived from models that do not contain these species. These aspects are regularly treated in quantum chemical studies of the electrocatalytic oxygen reduction reaction (ORR) by two electron (2e – ) and four electron (4e – ) pathways, − ,, which may have more similarities to direct synthesis of H 2 O 2 than initially expected. ,, The computational expense to implement models that include all the species crucial for H 2 O 2 formation will be greater, but the understanding gained from these studies would be valuable. Such work will need to be performed in close cooperation with experiments that provide kinetic parameters (e.g., activation enthalpies) and measure physical attributes of the catalyst surface (e.g., adsorbate coverages, oxidation states) that can be used to develop and validate these models.…”

Oxygen reduction reaction features in neutral media on glassy carbon electrode functionalized by chemically prepared gold nanoparticles

“…Oxygen reduction reaction (ORR) has gained a standing interest in the last 20 years as a result of the wide range of applications that it is involved in, such as chemical and biochemical analysis, pharmaceutics, corrosion, energy conversion, and fuel cells [1]. It has been, for a long time, one of the most studied redox processes, both from mechanistic [2,3] and kinetic [4][5][6] aspects. Indeed, several different mechanisms may be invoked to account for O 2 reduction, the most commonly reported being either a four-electron Bdirect^pathway (Reaction 1) [7] The main parameters that impact on mechanistic pathway are the operating media and electrode materials [8], and some authors have reported more complex reduction paths on alloys and noble metals [11].…”