Electrochemical oxygen reduction to hydrogen peroxide via a two‐electron transfer pathway on carbon‐based single‐atom catalysts

Electrochemical reduction of oxygen is considered as a new strategy to achieve decentralized preparation of hydrogen peroxide (H2O2) in a green manner. As a promising new type of catalytic material, carbon‐based single‐atom catalysts can achieve wide‐range adjustments of the electronic structure of the active metal centers while also maximize the utilization of metal atoms, toward electrochemical production of H2O2 from the selective two‐electron transfer oxygen reduction reaction (ORR). Herein, starting from the reviewing of characterizing methods and reaction mechanisms of ORR via two‐electron and four‐electron transfer pathways, the vital role of binding strength between OOH intermediate and active sites in determining the activity and selectivity towards H2O2 production is revealed and illustrated. Currently reported carbon‐based single‐atom catalysts for H2O2 production are systematically summarized and critically reviewed. Moreover, with the underpinning chemistry to improve the overall efficiency, three aspects concerning the central metal atoms, coordinated atoms, and environmental atoms are comprehensively analyzed. Based on the understanding of the most current progresses, some predictions for future H2O2 production via electrochemical routes are offered, which include catalyst designs at atomic levels, new synthesis strategies and characterization techniques, as well as interfacial superwetting interaction engineering at electrode and device levels

Strain Engineering to Enhance the Electrooxidation Performance of Atomic-Layer Pt on Intermetallic Pt₃Ga

Strain engineering has been a powerful strategy to finely tune the catalytic properties of materials. We report a tensile-strained two-to-three atomic-layer Pt on intermetallic Pt₃Ga (AL-Pt/Pt₃Ga) as an active electrocatalyst for the methanol oxidation reaction (MOR). Atomic-resolution high-angle annular dark-field scanning transmission electron microscopy characterization showed that the AL-Pt possessed a 3.2% tensile strain along the [001] direction while having a negligible strain along the [100]/[010] direction. For MOR, this tensile-strained AL-Pt electrocatalyst showed obviously higher specific activity (7.195 mA cm^–2) and mass activity (1.094 mA/μg_Pt) than those of its unstrained counterpart and commercial Pt/C catalysts. Density functional theory calculations demonstrated that the tensile-strained surface was more energetically favorable for MOR than the unstrained one, and the stronger binding of OH* on stretched AL-Pt enabled the easier removal of CO*

Metal (Hydr)oxides@Polymer Core–Shell Strategy to Metal Single-Atom Materials

Preparing metal single-atom materials is currently attracting tremendous attention and remains a significant challenge. Herein, we report a novel core–shell strategy to synthesize single-atom materials. In this strategy, metal hydroxides or oxides are coated with polymers, followed by high-temperature pyrolysis and acid leaching, metal single atoms are anchored on the inner wall of hollow nitrogen-doped carbon (CN) materials. By changing metal precursors or polymers, we demonstrate the successful synthesis of different metal single atoms dispersed on CN materials (SA-M/CN, M = Fe, Co, Ni, Mn, FeCo, FeNi, etc.). Interestingly, the obtained SA-Fe/CN exhibits much higher catalytic activity for hydroxylation of benzene to phenol than Fe nanoparticles/CN (45% vs 5% benzene conversion). First-principle calculations further reveal that the high reactivity originates from the easier formation of activated oxygen species at the single Fe site. Our methodology provides a convenient route to prepare a variety of metal single-atom materials representing a new class of catalysts