The surface passivation of Ge(100) and Ge(111) anodes in Ge–air batteries with different doping types and concentrations

The surface passivation of Ge(100) and Ge(111) anodes in Ge-air batteries with different doping types and concentrations is analyzed by density function theory (DFT) calculations. Compared with Ge(111) anodes, the surface passivation is restrained on Ge(100) anodes as they have larger binding energies with GeO2 layers. Meanwhile, doping would hinder the formation of a GeO2 layer on Ge anodes, especially for p-type doping, like B. The dissimilarities of the electrostatic potential differences and projected local density of states between the p-type Ge(100)/GeO2 and Ge(111)/GeO2 also reveal the origins of their distinct performances in Ge-air batteries. Furthermore, the I-V curves show that the Ge(100)/GeO2/Ge(100) device has a higher current than the Ge(111)/GeO2/Ge(111) device. This work would help to fundamentally comprehend the different electrochemical properties of Ge-air batteries with different orientations and doping and provide guidelines for the design of Ge anodes in Ge-air batteries.