With first-principles density functional theory calculations, we demonstrate that quantum capacitance of graphene-based electrodes can be improved by the N-doping, vacancy defects, and adsorbed transition-metal atoms. The enhancement of the quantum capacitance can be contributed to the formation of localized states near Dirac point and/or shift of Fermi level induced by the defects and doping. In addition, the quantum capacitance is found to increase monotonically following the increase of defect concentrations. It is also found that the localized states near Fermi level results in the spin-polarization effect.

An amorphous metal-free N-doped carbon film prepared by sputtering and annealing exhibits comparable electrocatalytic activity and superior stability and methanol tolerance to the commercial Pt/C catalyst via a four-electron pathway for oxygen reduction reaction (ORR). Pyridinic nitrogen in films plays a key role in electrocatalytic activity for ORR.

Two sets of thermal stable nanocomposites were fabricated by using engineering plastics poly(ether sulfone) (PES) as a matrix and phthalocyanine molecules (CuPc) or hyperbranched phthalocyanine (HCuPc)-coated barium titanate (BT) nanoparticles as fillers for high electric field and high-temperature dielectric applications. By side-by-side comparison, the hyperbranched coating is finely addressed for enhancing the dielectric response and breakdown strength of the composites. Specifically, BT-HCuPc/PES exhibits 40% lower dielectric loss and about 110% larger breakdown strength than BT-CuPc/PES. The addition of hyperbranched phthalocyanine may enhance the compatibility and dispersion of the ceramic fillers in the polymer matrix and reduces the charge carrier between the filler and matrix. Meanwhile, high dielectric constant, high breakdown, and low dielectric loss are well-maintained in the composites filled with hyperbranched phthalocyanine-modified BT from room temperature to 150 °C. The discharged energy density of the composites (20 vol % BT-HCuPc/PES) can reach 2.0 J/cm at 300 MV/m, about 166% of that of the polymer matrix (1.2 J/cm). Our findings on hyperbranched coating structure could be applicable to other ceramic-polymer composites to enhance their dielectric response.

We explore the stability, electronic properties, and quantum capacitance of doped/co-doped graphene with B, N, P, and S atoms based on first-principles methods. B, N, P, and S atoms are strongly bonded with graphene, and all of the relaxed systems exhibit metallic behavior. While graphene with high surface area can enhance the double-layer capacitance, its low quantum capacitance limits its application in supercapacitors. This is a direct result of the limited density of states near the Dirac point in pristine graphene. We find that the triple N and S doping with single vacancy exhibits a relatively stable structure and high quantum capacitance. It is proposed that they could be used as ideal electrode materials for symmetry supercapacitors. The advantages of some co-doped graphene systems have been demonstrated by calculating quantum capacitance. We find that the N/S and N/P co-doped graphene with single vacancy is suitable for asymmetric supercapacitors. The enhanced quantum capacitance contributes to the formation of localized states near the Dirac point and/or Fermi-level shifts by introducing the dopant and vacancy complex.