Two-dimensional g-CNs/GeC heterojunctions: desirable visible-light photocatalysts and optoelectronic devices

Designing efficient and feasible semiconductor visible-light photocatalysts holds great promise for photocatalytic hydrogen production. Herein, three heterojunctions, namely, C2N/GeC, C3N/GeC and g-C3N4/GeC, were designed and systematically explored using first-principles calculations. Through systematic research on electronic properties, it has been found that C2N/GeC and g-C3N4/GeC heterojunctions possess exceptional carrier mobility and display superior reaction mechanisms as Z-scheme heterojunctions, with an unique charge transfer pathway further boosting the separation of electron-hole pairs and suppressing carrier recombination. Additionally, suitable band edge potentials enable them to perfectly cross redox potentials for water splitting in the pH range 0-7. Gibbs free energy measurements confirm that the highly active HERs of the two Z-scheme heterojunctions are prone to conduction at the C sites of GeC layers, with Delta G values of -0.253 eV and -0.335 eV. Meanwhile, the two Z-scheme heterojunctions exhibit excellent OER performance with low overpotentials of 1.44 eV and 1.49 eV. Furthermore, the optical absorption abilities of C2N/GeC and g-C3N4/GeC heterojunctions are significantly improved within the visible and ultraviolet range, thus enhancing solar utilization efficiency. Consequently, C2N/GeC and g-C3N4/GeC heterojunctions feature remarkable photocatalytic abilities, which endow them the potential for use as Z-scheme visible-light photocatalysts for overall water splitting. Besides, though the C3N/GeC heterojunction belongs to type-I heterojunction, its outstanding carrier mobility and optical performance make it promising for optoelectronic devices. Briefly, this work delves into the photocatalytic reaction mechanism, providing theoretical reference for future research on highly productive photocatalysts. 2D g-CNs/GeC Z-scheme heterojunctions show excellent HER and OER performance.