Simultaneously Achieving High Activity and Selectivity toward Two-Electron O₂ Electroreduction: The Power of Single-Atom Catalysts

Abstract

On-site production of hydrogen peroxide (H2O2) using electrochemical methods could be more efficient than the current industrial process. However, due to the existence of scaling relations for the adsorption of reaction intermediates, there is a long established trade-off between the activity and selectivity of the catalysts, as the enhancement of catalytic activity is typically accompanied by a four-electron O2 reduction reaction (ORR), leading to the reduced selectivity for the H2O2 production. Herein, by means of density functional theory (DFT) computations, we reported the feasibility of several classes of important and representative experimentally achievable single-atom catalysts (SACs) toward two-electron ORR, paying attention to their stability, selectivity, and activity at the acidic medium. Starting from 210 two-dimensional (2D) SACs, we demonstrated that 31 SACs have the potential to break the metal-based scaling relations and simultaneously achieve high activity and selectivity toward H2O2 production and screened out 7 SACs with higher activity than the PtHg4 in acidic media. Especially, a noble metal-free SAC, namely, a single Zn atom centered phthalocyanine (Zn@Pc-N4), has a remarkable activity improvement with a small overpotential of 0.15 V. Moreover, using multivariable analysis and machine-learning techniques, we provided a comprehensive understanding of the underlying origin of the selectivity and activity of SACs and unveiled the intrinsic correlations between structure and catalytic performance. This work may pave a way to the design and discovery of more promising materials for H2O2 production.

Atomically dispersed Lewis acid sites boost 2-electron oxygen reduction activity of carbon-based catalysts

“…Besides, we explored the selectivity of the 2-electron process over the 4-electron process. As suggested by Guo et al 39 , for the electrocatalysts favoring the generation of H 2 O 2 rather than H 2 O, the potential barrier for H 2 O 2 desorption should be lower than that for the hydrogenation of OOH* to O*. The barriers are listed in Supplementary Table 3 , where one can see that the 2-electron process is thermodynamically favorable or comparable to the 4-electron process.…”

“…The total energy ( E ) and corresponding thermodynamic quantities, in eV, for free H 2 , H 2 O, H 2 O 2 species, were listed in Supplementary Table 8 39 . Since O 2 molecule is poorly described by standard DFT calculations, all the free energies were calculated by using the free energies of H 2 O (l) and H 2 (g) as ref.…”

Recent Progress on Carbonaceous Material Engineering for Electrochemical Hydrogen Peroxide Generation

“…However, the structure-activity relationship (especially the performance of single functional groups) remains unclear and needs to be further investigated by controllable experiments and precise DFT calculations. Other suitable catalysts can be found through DFT computations [53]. In addition, further attention should be given to topological structure design for active catalysts (actual determination of selectivity should be noted [54]) with high-current density, long-term run, and depressing the decomposition of H 2 O 2 at high overpotentials.…”

Catalyst Design for Electrochemical Oxygen Reduction toward Hydrogen Peroxide

“…and ligand effects hold the potential to break scaling relations for the adsorption of reaction intermediates, i.e., *O, *OOH and *OH, making room for ΔG HOO* and ΔG O* tuning toward a balanced improvement on H 2 O 2 production activity and selectivity. [95] Shown in Figure 5a,b are representatives of Co-N-C sites anchored on carbon substrates. Zhang et al synthesized a Co-N x -C site and oxygen functional group comodified carbon catalyst, exhibiting a H 2 O 2 selectivity over 80% in 0.1 m KOH and an early onset potential at 0.79 V versus RHE.…”