Selective H₂O₂ Electrosynthesis over Defective Carbon from Electrochemical Etching of Molybdenum Carbide

Abstract

The controllable synthesis of specific defective carbon catalysts is crucial for two-electron oxygen reduction reaction (2e − ORR) to generate H 2 O 2 due to the great potential applications. Herein, the defective carbon catalysts (Mo-CDC-ns) were prepared by an electrochemical activation (ECA) method with Mo 2 C/C as a parent. Electrochemical cyclic voltammetry curves, X-ray photoelectron spectroscopy, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and high-resolution transmission electron microscopy confirm the evolution process of a defective carbon structure from the Mo 2 C phase in which Mo species are first oxidized to Mo 6+ species and then the latter are dissolved into the solution and defective carbon is simultaneously formed. Raman and electron paramagnetic resonance spectra reveal that the defect types in Mo-CDC-ns are the edge defect and vacancy defect sites. Compared with the parent Mo 2 C/C, Mo-CDC-ns exhibit gradually increased kinetic current density and selectivity for H 2 O 2 generation with an extension of activation cycles from 10 (Mo-CDC-10) to 30 (Mo-CDC-30). Over Mo-CDC-30, a kinetic current density of 19.4 mA cm −2 and a selectivity close to 90% in 0.1 M KOH solution were achieved, as well as good stability for H 2 O 2 production in an extended test up to 12 h in an H-cell. Graphene planes and Stone Wales 5757-carbon were constructed as basic models for density functional theory calculations. It revealed that the obtained defective structure after the removal of Mo atoms contains the double vacancy at the edge of graphene (Edge-DVC) and the topological defect on the plane of 5757-carbon (5757C-D), which show more moderate reaction free energy for forming *OOH and smaller energy barrier of 2e − ORR.

Enhanced electrocatalytic performance for H2O2 generation by boron-doped porous carbon hollow spheres

“…Compared to the values of the onset potentials of the recently reported catalysts ( Figure 5 C), B-PCHS and PCHS in this study might be listed in the most active catalysts for 2e-ORR in alkali electrolytes. 9 , 13 , 17 , 24 , 33 , 32 , 34 , 35 , 36 , 37

Figure 5 The catalytic activity of the synthesized catalysts (A) The onset potential and half-wave potential of each catalyst. (B) The Tafel plots of different catalysts.

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Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

“…[441,442] In chemically etched Mo 2 C defects in constructed CAC materials, single-vacancy carbon (SVC), double-vacancy (DVC), and Stone Wales 5757 carbon (5757C) sites show lower 2e − ORR energy barriers and more moderate *OOH reaction-free energies than in pristine CAC materials, and single-vacancy carbon (Edge C-DVC) in edge positions and removal of the 5757C conformation The new topologically defective structure (5757C-D) with a moderate Bader charge (4.02-4.05) after the re-evolution of the Mo atoms located at the intersection of the pentagonal, hexagonal and heptagonal shapes has a moderate Bader charge (4.02-4.05), facilitating the adsorption and desorption of the intermediate *OOH and thus the generation of H 2 O 2 . [443]…”

Recent Advances and Future Perspectives of Transition Metal‐Supported Carbon with Different Dimensions for Highly Efficient Electrochemical Hydrogen Peroxide Preparation

“…used MoCl 3 as the metal source, and glucose as carbon source to prepare molybdenum carbide‐derived carbon catalysts (Mo‐CDC‐ns) through an electrochemical activation (ECA) method. [ 35 ] As illustrated in Figure 3 a, DFT calculations were used to simulate the adsorption models of *OOH on several defective carbons. Obviously, the topological defect on the plan of 5757‐carbon (5757C‐D) presented the minimum free energy ≈3.35 eV, which was close to the theoretical value ≈ 3.52 eV.…”

“…Reproduced with permission. [ 35 ] Copyright 2022, American Chemical Society. e) Relationships between H 2 O 2 , FE, Co dosage, and defects.…”