In situ growing N and O co-doped helical carbon nanotubes encapsulated with CoFe alloy as tri-functional electrocatalyst applied in Zn–Air Batteries driving Water Splitting

Currently, it is still a big challenge to develop highly active and robust trifunctional non-noble electrocatalysts to meet the practical application of renewable energy storage and conversion devices including metal-air batteries and water electrolyzers. N and O co-doped helical carbon nanotubes encapsulated with CoFe alloy (CoFe@NO-CNT) were prepared in situ on carbon paper using ZIF67 as precursor through ion exchange and chemical vapor deposition (CVD) pyrolysis methods. Comparative studies found that the heterogeneous catalysis of CoFe alloy produced spiral carbon nanotubes, which had a much higher N and O doping content than conventional carbon nanotubes containing monometallic cobalt particles. On the basis of the advantages of in situ growth and 3D open structure of catalytic electrode, the helical carbon nanotubes with abundant N catalytic species, C = O functional groups and core-shell structure exhibit superior electrocatalytic activity for ORR/OER/HER. The zinc-air battery (ZAB) and water electrolysis device based on CoFe@NO-CNT electrodes showed peak power density (142 mW/cm²), specific capacity (819 mAh/g_Zn), low overall water splitting voltage (1.57 v @ 10 mA/cm²) and good stability. Two CoFe@NO-CNT based ZABs in serial connection can efficiently drive the electrolyzer with two same CoFe@NO-CNT/CFP electrodes to split water and two quasi-solid state ZABs in series provide a peak power of 212 mW to light a red light-emitting diode (LED) indicator.