Carbon edges with gradient nanocarbons explored for electrochemical hydrogen peroxide production

(Nanowerk News) Doped carbon materials have shown great potential application toward H2O2 electrosynthesis from reduction of O2, and various heteroatoms species attached to carbon edges are suggested to be active evidenced by impressively experimental characterizations and theoretical calculations.
However, real contributions of intrinsic carbon edges (heteroatoms-free, unless otherwise specified, carbon edges referred to below are all heteroatoms-free) to H2O2 electrocatalytic production have lacked experimental insights as it is hard to study them in isolation from the coexistence of heteroatoms species. Moreover, identifying the specific structures and the roles of different carbon edges (e.g. zigzag and armchair configurations) experimentally remains a challenge.
In a study published in Matter ("Disclosing the natures of carbon edges with gradient nanocarbons for electrochemical hydrogen peroxide production"), the research group led by Prof. LIN Yangming from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a model method, in which different gradient nanocarbons with well-defined edge configurations and sizes are used as models to investigate the explicit function of each common edge at a molecular level.
The researchers found that both armchair and zigzag configurations are advantageous to H2O2 formation demonstrated by high selectivity of ~90%. The theoretically mass activities (up to 5451 A gnanocarbon-1) of dispersed nanocarbons on reasonable carbon support at 0.60 V versus reversible hydrogen electrode (VRHE) far exceed reported state-of-the-art catalysts.
Specifically, they established relatively precise structure (2D)-function relationships for electrochemical H2O2 production. Dynamic evolution of key intermediate products including O2 (ads) and superoxide anion O2-* at different carbon edges were identified and monitored experimentally with simulation calculation and in situ time-resolved ATR-IR spectra, respectively.
Besides, the researchers studied the kinetic behavior of intermediates. The results showed that O2 (ads) and O2-* species show a steep growth trend in the first 7.3 s~10 s and reach equilibrium until 10 s~13.3 s, respectively. The formation of O2-* from O2 (ads) coupled with the first electron transfer (that is, O2 (ads)+e-→O2-*) was suggested to be an unexpectedly possible rate-determining step.
This study provides a new understanding for carbon edges in metal-free carbon-based catalysis.
Source: Chinese Academy of Sciences
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