Creation of Ge-N_x-C_y Configures in Carbon Nanotubes: Origin of Enhanced Electrocatalytic Performance for Oxygen Reduction Reaction

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 (a0.08 V). The high ORR performance is attributed to the synergistic effect of N and Ge doping, which is capable of activating the electrons of sp² 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).