Quantum capacitance engineering in boron and carbon modified monolayer phosphorene electrodes for supercapacitor application: A theoretical approach using ab-initio calculation

In this work, for the first time, the effects of Boron (B) and Carbon (C) substitutional doping/co-doping on the quantum capacitance of monolayer Phosphorene (Ph) have been extensively investigated for electrode design of electrical double-layer (EDL) supercapacitor. In this context, the effects of different doping concentrations on local charge distribution, energy band structure, and density of states have been systematically correlated with the quantum capacitance variation with local electrode potential. In pristine Ph, the presence of a large energy bandgap and the absence of states therein severely compromise the quantum capacitance at lower electrode potential compared to pristine Graphene (Gr). The B and C both act as acceptor-type impurities in Ph and tend to shift the Fermi level towards the valence band edge. Specifically, the introduction of B-doping induces localized defect states near the conduction band edges. This leads to a moderate improvement in quantum capacitance for a relatively larger electrode potential. In contrast, the C doping and B/C co-doping introduce de-localized defect states around the Fermi level near the valence band edges, which ensures a significantly larger quantum capacitance compared to pristine Gr and Ph over the range of −1.0 V to 1.0 V electrode potential.