Overall Water Splitting of the Direct Z-Scheme vdW Heterojunction GeC/ZrS₂

Direct Z-scheme heterojunctions can realize the effective space separation of electrons and holes under light radiation. Therefore, it has an obvious advantage for water splitting. In this work, we have designed and studied a new heterojunction, GeC/ZrS2, with a direct Z-scheme band arrangement. Both monolayer GeC and monolayer ZrS2 in the present GeC/ZrS2 heterojunction are easily prepared. We also systematically investigated the electronic and optical properties of the GeC/ZrS2 heterojunction. The calculated binding energy and phonon spectra show that the GeC/ZrS2 heterojunction has good stability. The electronic structure and band arrangement show that GeC/ZrS2 is a direct Z-scheme energy band arrangement with a suitable band gap (1.19 eV) for photocatalytic water decomposition. The GeC/ZrS2 heterojunction shows good absorption coefficients (reaching 105 cm–1) in the visible and ultraviolet ranges. The GeC/ZrS2 heterojunction has excellent carrier mobilities in both the armchair and zigzag directions, and the electron mobility can reach 1502.78 cm2 V–1 s–1 in the zigzag direction, which is good for the space separation of electrons and holes under light radiation. The Gibbs free energy shows that the GeC/ZrS2 heterojunction can achieve overall water splitting at pH = 14 and an external voltage of 3.3 eV. The solar to hydrogen (STH) production efficiency is 28.7%. Moreover, the GeC/ZrS2 heterojunction can achieve a direct Z-scheme band arrangement, and the biaxial strain can further increase the band gap and improve the photocatalytic performance. Our results show that the heterojunction GeC/ZrS2 has excellent potential for overall photocatalytic water splitting.