For ORR reaction, CB has a higher initial potential than Gr, indicating that CB has better catalytic activity than Gr. After the addition of PTFE, the initial potential of oxygen reduction increases and moves towards the direction of thermodynamic equilibrium potential, indicating that the catalytic activity of PTFE is improved. In Fig.S2e, the open circuit potential of Gr under the condition of saturated dissolved oxygen is 0.147v, which is far less than that of CB (0.825v), indicating that the surface of Gr has less oxygen adsorption and basically no oxygen reduction catalytic activity, which is consistent with the previously characterized small specific surface area of Gr and fewer defects. For CB, due to the large specific surface area and more defects, the oxygen adsorbed on the surface of CB has a greater tendency to undergo reduction reaction, and 0.825v is higher than the standard potential of 0.69v of 2e-reduction mechanism of oxygen, indicating the existence of 4e-reduction mechanism for CB.
After adding PTFE, the open circuit potential of Gr becomes 0.328v, but it is still far away from the standard potential of 0.7v, with poor activity. CB is compounded with Gr and added with PTFE (Gr0.5CB0.5/PTFE0.5), with an open-circuit potential of 0.786V, which is close to the oxygen 2e-reduction potential. Peer’s study[73] has also shown that the addition of PTFE can change the surface polarity of the material and increase the affinity adsorption capacity of oxygen. Whether the open circuit potential is closer to the standard potential and the selectivity of hydrogen peroxide generation is better still needs further experimental study.
In addition to increasing the activity of active sites, there are strategies to increase the number of active sites that affect the rate of hydrogen peroxide formation. By observing the variation trend of the capacitance reflecting the surface roughness of the electrode in Fig.S2d and the electrochemical active surface area in Table.1, we are surprised to find that the electrochemical active surface area with PTFE significantly increases, even though the electrochemical active surface area of PTFE with Gr is higher than that of the original CB material, indicating that the addition of PTFE significantly increases the number of active sites. This shows the important role of adding PTFE in promoting the formation of hydrogen peroxide. It can also be considered that the addition of PTFE resulted in the formation of hierarchical pore structure, and the presence of polymer phase also improved the affinity of catalyst surface to gas. More three-phase interfaces are constructed by the two kinds of interaction. This structure is conducive to oxygen transfer, oxygen adsorption and 2e-activation, thus improving the hydrogen peroxide generation rate and Faraday efficiency.

3.3 The performance of synthesis H2O2 in a H-type cell