High-performance nitrogen and germanium codoped carbon nanotubes (N-Ge-CNTs) were synthesized as oxygen reduction reaction (ORR) catalysts by one-step sintering of carboxyethyl germanium sesquioxide and multiwalled CNTs in NH3 atmosphere. The ORR electrocatalytic activity evaluation was performed by using limited current density, selective reaction pathway, onset potential, H2O2 yields, and kinetic current density. In comparison with Ge or N solely doped CNTs, the codoped samples display more excellent ORR catalytic performance. It was observed that the codoped GeN3C, GeN4, and GeN4 + NC3 microstructures in N-Ge-CNTs are crucial to improving ORR catalytic performance, such as ideal 4 electron pathway (3.95) and positive onset potential (-0.08 V). The high ORR performance is attributed to the synergistic effect of N and Ge doping, which is capable of activating the π electrons of sp(2) hybridized orbital around carbon nantotubes. The ORR catalytic synergistic effect has also been verified by calculating the work function on the basis of density functional theory (DFT).
Keywords: Ge/N codoping; carbon nanotubes; oxygen reduction reaction; synergistic effect.