Highly active and selective oxygen reduction to H2O2 on boron-doped carbon for high production rates

Oxygen reduction reaction towards hydrogen peroxide (H2O2) provides a green alternative route for H2O2 production, but it lacks efficient catalysts to achieve high selectivity and activity simultaneously under industrial-relevant production rates. Here we report a boron-doped carbon (B-C) catalyst which can overcome this activity-selectivity dilemma. Compared to the state-of-the-art oxidized carbon catalyst, B-C catalyst presents enhanced activity (saving more than 210 mV overpotential) under industrial-relevant currents (up to 300 mA cm−2) while maintaining high H2O2 selectivity (85–90%). Density-functional theory calculations reveal that the boron dopant site is responsible for high H2O2 activity and selectivity due to low thermodynamic and kinetic barriers. Employed in our porous solid electrolyte reactor, the B-C catalyst demonstrates a direct and continuous generation of pure H2O2 solutions with high selectivity (up to 95%) and high H2O2 partial currents (up to ~400 mA cm−2), illustrating the catalyst’s great potential for practical applications in the future.

The trace amount of oxygen species remained comes from the adsorption of water and air during XPS sample preparation and transportation (see more details in Supplementary Figure 15). Note that a.u. represents arbitrary units.

Faradaic efficiency (FE) in Rotating Ring-Disk Electrode (RRDE) measurement.
Note that the increase in FE does not obey the same linear relationship as that of molar selectivity. The peak located at ~533 eV for all the samples corresponds to π-bonded oxygen on carbon surface either from trace amount of oxygen dopant which is impossible to remove when annealing the samples at the high temperature (750 o C) or due to the oxidation during the sample exposure to air. The peaks around 535 eV and 540 eV are assigned to surface adsorbed/residual water species, which is consistent with our XPS results shown in Supplementary Figure 15. Note that a.u. represents arbitrary units. Figure 17. High resolution TEM image of CB. Note that the local structure in nano-meter scale is exactly graphene-like structure. Actually, the structure of carbon black is comparable to graphite: both are composed of graphene sheets, while graphite's layers are typically larger and more ordered than carbon black whose sheets form 3-dimensional structure. Based on this information, graphene structure is typically used to represent carbon black for modelling electrochemistry 2,3 . Considering the 3dimensional structure of carbon black would be too large for DFT modeling while chemical reaction typically takes place at ~1 nm scale, we believe using graphene as the carbon structure in our simulations is appropriate to our best computational resources. Figure 18. Illustration of six adsorption sites that considered in this work. The orange sphere represents the dopant atom while the grey spheres are the carbon atoms. 1,2,3,4,5,6 sites are named as "SV", "C-SV", "DV", "C-DV", "5577" and "C-5577" respectively.   If we are operating the solid-electrolyte cell under highest H2O2 production rate condition (see Figure 6c): 2.55 V (500 mA, ~0.84 wt.% H2O2), with a H2O2 production rate of 7.36 mmol cm -2 h -1 (1.00096 g h -1 ). The mass of H2O2 generated using 1 kWh of electricity will be: for O2 price; but in reality, the cost is even lower). Please note that the O2 cost can be further reduced by collecting and recycling O2 gas produced from OER on the anode side.

Supplementary
(b) Assuming the price of electricity is 3 cents/kWh 14 , we can roughly estimate a electricity for H2O2 production to be $0.038/kg-H2O2.
In summary, the total energy and feed stock cost is less than about $1.1/kg-H2O2.
Since the largest portion of the cost is from deionizing water, the cost can be further reduced in the future by replacing DI water feed stock with industrial water plus water filter. Furthermore, our on-site generation method does not need the cost for transportation and storage. In comparison, the traditional industrial anthraquinone process for H2O2 production has a rough cost of $1.5/kg-H2O2 without transportation