Electrosynthesis of H2O2 Promoted by π-π Interaction on a Metal-Free Carbon Catalyst.

The synthesis of hydrogen peroxide (H2O2) through electrocatalytic oxygen reduction reaction is an ideal alternative to the current energy-intensive anthraquinone process, but developing cost-effective and high-efficiency electrocatalysts is still challenging. Herein, a metal-free graphitic carbon nitride/carbon nanotube (g-C3N4/CNT) hybrid catalyst can enhance H2O2 production via π-π interaction is reported, achieving almost unity (97%) H2O2 production at 0.57 V with high selectivity of over 92% across the wide potential range from 0.6 to 0 V. Other carbon materials with weak interaction with g-C3N4, such as acetylene black and super P, show markedly weakened H2O2 production, indicating the importance of π-π interaction. Electron transfer kinetic analysis combined with density functional theory calculations indicates that the synergistic effect between g-C3N4 and CNT enhances electron transfer and O2 activation between g-C3N4 and CNT, leading to enhanced H2O2 production performance. This work provides a complementary approach for H2O2 production from oxygen reduction besides introducing oxygenated groups or heteroatom doping into carbon materials.

Rational design of heterogenized molecular phthalocyanine hybrid single-atom electrocatalyst towards two-electron oxygen reduction.

Single-atom catalysts supported on solid substrates have inspired extensive interest, but the rational design of high-efficiency single-atom catalysts is still plagued by ambiguous structure determination of active sites and its local support effect. Here, we report hybrid single-atom catalysts by an axial coordination linkage of molecular cobalt phthalocyanine with carbon nanotubes for selective oxygen reduction reaction by screening from a series of metal phthalocyanines via preferential density-functional theory calculations. Different from conventional heterogeneous single-atom catalysts, the hybrid single-atom catalysts are proven to facilitate rational screening of target catalysts as well as understanding of its underlying oxygen reduction reaction mechanism due to its well-defined active site structure and clear coordination linkage in the hybrid single-atom catalysts. Consequently, the optimized Co hybrid single-atom catalysts exhibit improved 2e- oxygen reduction reaction performance compared to the corresponding homogeneous molecular catalyst in terms of activity and selectivity. When prepared as an air cathode in an air-breathing flow cell device, the optimized hybrid catalysts enable the oxygen reduction reaction at 300 mA cm-2 exhibiting a stable Faradaic efficiency exceeding 90% for 25 h.