Tailoring Heteroatoms in Conjugated Microporous Polymers for Boosting Oxygen Electrochemical Reduction to Hydrogen Peroxide

Heteroatom-doped metal-free carbon materials have been considered as efficient catalysts for electrochemical H2O2 production via the two-electron oxygen reduction reaction (2e--ORR). However, it is difficult to construct the precise heteroatom-doped carbon materials driving the 2e--ORR process through the conventional pyrolytic method. Reported here is a diatomic hetero-cyclization strategy to construct efficient 2e--ORR catalysts based on poly-benzimidazole, poly-benzoxazole, and poly-benzothiazole (PBXs, X = I, O, and T), which are composed of N-NH-, N-O-, or N-S-heterocycles, respectively. Poly-benzothiazole (PBT) with N, S-doped heterocyclic rings exhibit a higher H2O2 selectivity (95.6%) over corresponding undoped imine-based polymers (21.7%) and maintain remarkable electrochemical durability, which are among the highest values for PBXs as 2e--ORR catalysts. A maximum H2O2 production rate of 3.13 mol gcatalyst-1 h-1 is obtained at a fixed current density of 100 mA cm-2. Moreover, a remarkable Faradaic efficiency (F.E.) of 96% as well as good catalyst stability maintained over 50 h of testing over the PBT catalyst in the three-phase flow cell is achieved. Density functional theory (DFT) calculations reveal that the atomic spin density distribution of the corresponding carbon active sites in PBXs contributes to the high electrochemical performance in the 2e--ORR process. These results thus present that atomic-scale doping of sulfur atoms will strongly boost H2O2 production via affecting adjacent carbon atoms.