Contribution value of carbon edge structure during electrochemical synthesis of hydrogen peroxide

On April 28, 2022, Lin Yangming’s team at the Fujian Institute of Material Structure of the Chinese Academy of Sciences published a new study titled “Disclosing the natures of carbon edges with gradient nanocarbons for electrochemical hydrogen peroxide production” in the journal Matter.

By introducing gradient nanocarbon-based molecules, the research group revealed the true contribution value of the edge structure (no heteroatoms) of carbon materials in the electrochemical synthesis of H2O2, constructed a two-dimensional and accurate structure-activity relationship between the edge structure and the performance of electrosynthetic H2O2, and monitored and identified the key intermediate products and their time-resolved reaction kinetic behaviors. The only corresponding author of the paper is Lin Yangming.

Using the two-electron pathway to achieve electrocatalytic oxygen reduction reaction (ORR) is currently a new green method for synthesizing hydrogen peroxide (H2O2). After years of reporting, doped carbon materials have been confirmed to have good potential applications in H2O2 electrosynthesis, and various experimental characterizations and theoretical calculations have shown that heteroatoms at the edge of carbon materials (such as O atoms) are the main active sites. Considering the complexity of the surface of carbon materials, for example, the edges of carbon materials tend to adsorb different heteroatoms, so there has been a lack of experimental proof for the true contribution of individual carbon material edges (no heteroatoms) in the electrocatalytic synthesis of H2O2.

Recently, a team of researchers from Lin Yangming, Fujian Institute of Physical Structure, Chinese Academy of Sciences, used gradient carbon nanocarbons (PAHs) with clear topological edges and different sizes as model catalysts to try to study the specific functions of different edge structures at the molecular level. By using gradient PAHs model carbon nanocarbons to reveal the inherent properties of common handrails and zigzag edges, the experiment observed the dynamic behavior of key intermediates that occur at the edges of carbon during the electrochemical generation of H2O2, which brought new opportunities for the study of other electrocatalytic reactions.

Establishment of two-dimensional precision structure-activity relationship. Experimentally, it was proved that both handrail and zigzag edges have a positive effect on H2O2 synthesis, with selectivity of ~90%, and similar starting potentials, and by precisely controlling the latitude and longitudinal extension of PHAs, the structure-activity relationship between the size/quantity/area/area and activity of handrail or zigzag edges was established at the molecular level. At the same time, by efficiently dispersing the gradient model of nanocarbon molecules, their mass activity is close to 5500 A/g. By building a micro-flow cell, it was also found that carbon molecules have good practical value.

Figure 1: Structure-activity relationship and electrochemical properties of THE PAHs model catalyst.

Monitoring and reaction kinetics of active intermediate species. The dynamic evolution process and dynamic behavior of key intermediate products O2(ads) and superoxide anion O2-* were monitored by time-resolving infrared spectroscopy, isotope labeling and simulation calculations, and the peak position attribution of O2-* on handrail and zigzag carbon structures was discussed in detail, that is, 1163 cm-1 and 1206 cm-1 belonged to O2-* on handrail and zigzag carbon structures, respectively. Experimental angles show that O2(ads) forming O2-* (i.e., O2(ads)+e-→O2-*) is a possible rapid step. The time-resolved results showed that in different carbon edge structures, O2(ads) and O2-* showed a sharp increase trend at the initial 7.3 s to 10 s, respectively, and reached equilibrium at 10 s to 13.3 s. However, the time for O2 (ads) and O2-* species to reach dynamic equilibrium is shorter on the zigzag carbon structure.

Figure 2: In situ infrared spectra, isotope labeling, and simulation calculation studies of intermediate products on PHAs of different edge structures.

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Figure 3: Time-resolved in situ infrared spectra of O2(ADS) and superoxide anion O2-*.

In summary, the study describes an effective strategy for nanoscale PHAs as model carbon catalysts to study carbon-based electrocatalytic reaction mechanisms. This method provides an experimental basis for revealing the true contribution value of handrail and zigzag edges in H2O2 synthesis, and for the first time observes the real-time evolution and reaction dynamic behavior of key intermediates in the electrochemical formation of H2O2 at carbon edges, thus providing an effective reference for the study of other carbon-based electrocatalytic reactions. (Source: Science Network)

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