Self-Catalyzed Growth of Co-N-C Nanobrushes for Efficient Rechargeable Zn-Air Batteries.

Highly efficient and stable bifunctional electrocatalysts for oxygen reduction and evolution are essential for aqueous rechargeable Zn-air batteries, which require highly active sites as well as delicate structural design for increasing effective active sites and facilitating mass/electron transfer. Herein, a scalable and facile self-catalyzed growth strategy is developed to integrate highly active Co-N-C sites with 3D brush-like nanostructure, achieving Co-N-C nanobrushes with Co,N-codoped carbon nanotube branches grown on Co,N-codoped nanoparticle assembled nanowire backbones. Systematic investigations suggest that nanobrushes deliver significantly improved electrocatalytic activity compared with nanowire or nanotube counterparts and the longer nanotube branches give the better performance. Benefiting from the increase of accessible highly active sites and enhanced mass transfer and electron transportation, the present Co-N-C nanobrush exhibits superior electrocatalytic activity and durability when used as a bifunctional oxygen catalyst. It enables a rechargeable Zn-air battery with a high peak power density of 246 mW cm-2 and excellent cycling stability. These results suggest that the reported synthetic strategy may open up possibilities for exploring efficient electrocatalysts for diverse applications.

Molecular Evidence for Metallic Cobalt Boosting CO2 Electroreduction on Pyridinic Nitrogen.

Nitrogen-doped carbon materials (N-Cmat ) are emerging as low-cost metal-free electrocatalysts for the electrochemical CO2 reduction reaction (CO2 RR), although the activities are still unsatisfactory and the genuine active site is still under debate. We demonstrate that the CO2 RR to CO preferentially takes place on pyridinic N rather than pyrrolic N using phthalocyanine (Pc) and porphyrin with well-defined N-Cmat configurations as molecular model catalysts. Systematic experiments and theoretic calculations further reveal that the CO2 RR performance on pyridinic N can be significantly boosted by electronic modulation from in-situ-generated metallic Co nanoparticles. By introducing Co nanoparticles, Co@Pc/C can achieve a Faradaic efficiency of 84 % and CO current density of 28 mA cm-2 at -0.9 V, which are 18 and 47 times higher than Pc/C without Co, respectively. These findings provide new insights into the CO2 RR on N-Cmat , which may guide the exploration of cost-effective electrocatalysts for efficient CO2 reduction.