Nitrogen-deficient g-C3N4 compounded with NiCo2S4 (NiCo2S4@ND-CN) as a bifunctional electrocatalyst for boosting the activity of Li-O2 batteries

The bifunctional electrocatalytic material that has a catalytic effect on oxygen reduction (ORR) and oxygen evolution reactions (OER) is effective to reduce the development bottleneck of Li-O 2 batteries. Herein, g-C 3 N 4 was denitrogenated to obtain the nitrogen-deficient graphitic carbon nitride (noted as ND-CN) to improve its intrinsic conductivity while retaining part of the nitrogen active sites, and a transition metal composite electrocatalyst NiCo 2 S 4 @ND-CN (noted as NCS@ND-CN) was synthesized using a facile hydrothermal method. The porous structure of ND-CN provides a large specific surface area, which is conducive to exposing more active sites. In addition, the synergistic effect between the double transition metal and ND-CN improves the electrocatalytic activity of the catalyst. As expected, NCS@ND-CN shows excellent OER (low overpotential of 294 mV at 10 mA cm −2 in 1.0 M KOH solution) and ORR (half-wave potential of 0.84 V) activities. Remarkably, the Li-O 2 battery assembled with NCS@ND-CN exhibits an improved overpotential of 1.01 V, a high discharge capacity of 9660 mAh g −1 at 100 mA g −1 and a long-term cycle stability under a restricted capacity of 1000 mAh g −1 at 100 mA g −1 . • Composite of nitrogen-deficient g-C 3 N 4 and NiCo 2 S 4 (NiCo 2 S 4 @ND-CN) was synthesized. • ND-CN exhibiting high conductivity and high content of pyridine-N boosts activity. • NiCo 2 S 4 @ND-CN with large surface area is beneficial to uniform deposition of Li 2 O 2 . • Coupling of NiCo 2 S 4 and ND-CN boosts the bifunctional electrocatalytic activity.