First-principles calculation of monolayer PdSe₂ doped with Zn via single atom substitution and its effect on quantum capacitance

Abstract The discovery of two-dimensional materials, such as graphene, has sparked significant interest within the scientific community due to their unique properties. These materials offer a high surface area to mass ratio, making them ideal candidates for supercapacitor electrodes. Another promising material gaining attention is the monolayer palladium diselenide or PdSe 2 , a semiconductor known for its adjustable band gap within the transition metal dichalcogenides group. With fewer available states near the Fermi level in PdSe 2 , quantum effects become more pronounced, suggesting that its capacitance is strongly influenced by its electronic structure. This research aims to improve on the quantum capacitance of monolayer PdSe 2 using single atom substitution using Zn. Three systems of 2x2 unit cell sizes were constructed, namely pristine monolayer PdSe 2 , and Pd and Se substituted PdSe 2 with Zn. The formation energies of the three systems were probed to gauge their stability, the pristine system has a formation energy of −0.265 eV, while the Pd and Se substituted systems were observed to have 0.0238 eV and 0.0520 eV respectively. The calculated Bader charge interactions indicated that the Zn atom of the Se substituted system acts as an electron donor, while the Zn acts as electron acceptor for the Pd substituted system. Once doped with Zn, the bandgap energy closed from 1.10 eV to 0.50 eV for the Pd substituted system, and to 0.80 eV for the Se substituted system. An increase in quantum capacitance and surface charge were observed for both systems, most notably the Se substituted system which was observed to have a peak quantum capacitance of 200 μF/cm 2 at −0.2 V. The results show that doping with Zn via substitution decreased the occupiable states near the fermi level, thus increasing the quantum capacitance, making it a relatively better material for supercapacitor electrodes.