New strategies to improve two-electron oxygen reduction reaction selectivity of polypyrrole-based catalysts

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 11; no. 5; pp. 2168 - 2177
• Main Authors: Wang, Miaohui, Wang, Jianhua, Huang, Peipei, Lin, Haiping, Li, Qing
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 31.01.2023
• Subjects: Carbon; Catalysts; Chemical bonds; Chemical reduction; Chemical synthesis; Density functional theory; Electrochemistry; Hydrogen bonding; Hydrogen peroxide; Nitrogen; Oxygen; Oxygen reduction reactions; Polypyrroles; Selectivity
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta07936d

Direct electrochemical synthesis via the two-electron oxygen reduction reaction (ORR) is considered an environmentally friendly means to produce hydrogen peroxide (H 2 O 2 ). Metal-free N-doped carbon materials are reported to display good electrocatalytic performance for H 2 O 2 generation. Herein, we found that selectivity toward H 2 O 2 production in the ORR can be further enhanced once the N atoms are saturated bonds in polypyrrole. Saturation can either be achieved by stabilizing the N-H bonds via hydrogen-bonding interactions during preparation or transforming the deprotonated nitrogen species into C-N bonds by calcining polypyrrole at appropriate temperatures. Eventually, our synthesized catalyst NPC-400 exhibits a 94% H 2 O 2 selectivity and impressive stability. The mechanisms are elucidated by using control experiments and density-functional theory calculations. The α carbon atoms of pyrrolic-N are the active sites for selective H 2 O 2 production. However, once the N atoms are not saturated, the OOH* intermediate species tend to bond with the N atoms, leading to relatively poor reaction selectivities. Our work provides new insight for designing high selectivity catalysts for H 2 O 2 generation in the oxygen reduction reaction. Stabilizing N-H bonds by the hydrogen-bonding interaction in polymerization or transforming the deprotonated -N + - species into C-N bonds by calcining polypyrrole-based catalysts can improve the electrochemical two-electron oxygen reduction reaction.