Co–doped nitrogenated carbon nanotubes encapsulating CoNi alloys as bifunctional catalysts for urea-assisted rechargeable Zn-air battery

As a desirable alternative for oxygen evolution reaction (OER), urea oxidation reaction (UOR) with the effectively reduced overpotential has attracted considerable attention in pollutant degradation and rechargeable Zn-air battery (ZAB). Herein, a bifunctional electrocatalyst with CoNi alloy and CoN dual active sites encapsulated by nitrogen-doped carbon nanotubes have been rationally designed and successfully prepared. The as-obtained catalyst CoNi/Co–NCNT displays excellent catalytic activity for oxygen reduction (ORR) and UOR with a narrow potential difference of 0.56 V. The urea-assisted rechargeable ZABs based on CoNi/Co–NCNT provide higher energy conversion efficiency (61%), 15% higher than that of conventional ZABs. In addition to verify the UOR pathway on the CoNi/Co–NCNT, DFT calculations reveal that CoNi alloy and CoN in CoNi/Co–NCNT synergistically function as the main active sites for ORR and UOR. The excellent ORR catalytic performance and the superior energy conversion efficiency of CoNi/Co–NCNT based urea-assisted rechargeable ZAB is expected to accelerate the practical application of ZAB technology. This work paved a new way for the development of bifunctional catalysts for higher efficiency ZABs, and also provides a potential scheme for disposing urea rich wastewater.