Uncovering two-dimensional semiconducting honeycomb-kagome germanene for superior water splitting performance

Abstract Designing semiconducting two-dimensional materials with promising applications in optoelectronic and energy-related fields is challenging. Herein, we theoretically realize a semiconducting 2D-germanium (hhk-germanene) by introducing kagome topology into a honeycomb spatial configuration. The hhk-germanene breaks this mirror symmetry along the out-of-plane direction by having intrinsic dipole moments. Its bandgap falls between the Dirac-cone and flat-band dispersions due to the hybridization of Dirac electrons and the antiferromagnetic spin frustration, demonstrating high electron mobility and visible solid absorption. Strain tunable electrostatic potential difference can meet the thermodynamic requirements in photocatalytic water-splitting. Single TM atoms anchored hhk-germanene (TM@Ge) were considered in water-splitting, indicating Zr@Ge (0.086 V) and Rh@Ge (0.084 V) as efficient HER catalysts and Ni@Ge (0.40 V) and Ir@Ge (0.44 V) as superior OER catalysts due to their low overpotentials. Finally, multiple-level descriptors ( $$\Delta G_{OH*}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mmultiscripts> <mml:mi>G</mml:mi> <mml:mrow> <mml:mi>O</mml:mi> <mml:mi>H</mml:mi> <mml:mrow/> <mml:mo>∗</mml:mo> </mml:mrow> <mml:mrow/> </mml:mmultiscripts> </mml:mrow> </mml:math> , ε d , ICOHP, p - d hybridization) are established to clarify the activity origin of water splitting.