Understanding the Effect of Germanium as an Efficient Auxiliary Pre‐Dopant in Carbon Nanotubes on Enhancing Oxygen Reduction Reaction

Abstract

In this study, sulfur‐doped carbon nanotubes with germanium as a pre‐dopant (SGe‐CNTs) are successfully prepared by sequential doping of germanium and sulfur, and their activity oxygen reduction reaction (ORR) activity is evaluated. As comparison, Ge‐doped CNTs and S‐doped CNTs are synthesized. The electrochemical results reveal that both Ge‐doping and S‐doping could improve the ORR activity of CNTs. In the synthesis process of SGe‐CNTs, germanium is deemed to be an efficient auxiliary pre‐dopant, since germanium modifies the microstructure of CNTs, and germanium content on the surface of Ge‐CNTs decreases dramatically after sulfur doping. Meanwhile, sulfur content on the surface of SGe‐CNTs is much higher than that of S‐CNTs with equivalent sulfur‐comprising dopants. Due to the Ge pre‐doping effect and synergistic effect of S/Ge doping, SGe‐CNTs with appropriate ratio of Ge and S atoms exhibit prominently enhanced ORR performance compared with those of single Ge‐ or S‐doped CNTs. By virtue of the outstanding ORR performance, SGe‐CNTs materials are expected to be highly active and cost‐effective ORR electrocatalysts in metal‐air batteries and alkaline fuel cells. The excellent ORR catalytic performance of SGe‐CNTs could be ascribed to the auxiliary Ge pre‐doping effect.

In Situ Mechanistic Insights for the Oxygen Reduction Reaction in Chemically Modulated Ordered Intermetallic Catalyst Promoting Complete Electron Transfer

“…Figure j–l shows the fitted XPS plots for Pd 3d, Ge 3d, and Pt 4f edges, respectively, of Pt 0.2 Pd 1.8 Ge. It validates the presence of Pd, Ge, and Pt in metallic states at binding energies of 335.46, 28.92, and 71.49 eV with a slight presence of PdO, GeO and GeO 2 , and Pt oxides, respectively, on the surface due to surface oxidation . It can be concluded that after substitution, Pt stays in a slightly higher oxidation state with a decrease in the Pd oxidation state.…”

“…It validates the presence of Pd, Ge, and Pt in metallic states at binding energies of 335.46, 28.92, and 71.49 eV with a slight presence of PdO, GeO and GeO 2 , and Pt oxides, respectively, on the surface due to surface oxidation. 29 It can be concluded that after substitution, Pt stays in a slightly higher oxidation state with a decrease in the Pd oxidation state. This signifies that charge transfer from Pt to Pd takes place, which backs up the observation obtained from XANES analysis.…”

“…26,27 It is reported that Ge is stable in alkaline conditions and under reduction potentials of the ORR as well. 28,29 Considering the stability provided by Ge, we were curious to check the activity of Pd 2 Ge in the alkali-mediated ORR. Although the current density of Pd 2 Ge in the ORR was close to that of the state-ofthe-art Pt/C catalyst, we desired for enhancing the onset potential close to the theoretical value and improving the selectivity of 4e − transfer forming H 2 O.…”

Fabricating N, S Co‐Doped Hierarchical Macro‐Meso‐Micro Carbon Materials as pH‐Universal ORR Electrocatalysts**

“…At present, there are many non‐Pt‐based catalysts [8–12] that have been studied, such as transition metal‐based catalysts [13–17] and heteroatom‐doped carbon‐based catalysts [18–22] . Among them, heteroatom‐doped carbon‐based materials with obvious advantages of high conductivity, good durability and excellent activity have attracted considerable attention in recent years [23] . The synergistic construction of heteroatom co‐doping and generating hierarchical architecture is regarded as one of the most promising methods for achieving outstanding ORR carbon materials [24–26] .…”

The study of oxygen reduction reaction on Ge‐doped MoS 2 monolayer based on first principle

“…45,46 Germanium (Ge), as one kind of semiconductor materials, has been proved to be an effective heteroatom to enhance the catalytic activity of carbon nanotube (CNT) toward ORR. 47,48 The co-doping of Ge and nitrogen, sulfur, or phosphorus into CNT exhibits outstanding activity for ORR compared with solely heteroatom-doped CNT. The improved performance is due to the fact that the doping of Ge could change the electronic and physical properties of carbon materials, resulting in the improvement in ORR performance.…”