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Cobalt–iron sulfides supported on N-doped carbon were synthesized as energy storage material using ball milling followed by carbonization. As-synthesized materials were structurally analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Furthermore, cobalt–iron sulfides supported on N-doped carbon were coated on Ni foam, and their electrochemical performance was tested in a 3-M KOH electrolyte. The as-fabricated Co–Fe–S-2 electrode registered a specific capacitance of 1252 F g−1 at 1 A g−1 and also showed capacitance retention of 66.4% at 20 A g−1. In addition, asymmetric supercapacitors (ASC) were fabricated using the as-synthesized electrode materials and it had a voltage window of 0–1.6 V. Among them, the activated carbon (AC)//Co–Fe–S-2 ASC device showed maximum specific capacitance of 169.3 F g−1 at 1 A g−1, and it registered maximum energy density of 59.6 Wh kg−1 at power density of 0.796 kW kg−1. The AC//Co–Fe–S-2 device delivered a rate capability of 55.6% at 30 A g−1, and it reveals a capacitance retention of 76.3% over 5000 cycles. Herein we also found that ball-milling-assisted synthesis of Co–Fe–S-2 electrode material is a promising candidate for high-performance ASCs.

The key to popularizing proton exchange fuel cells is developing highly active, stable, and cost-effective catalysts for oxygen reduction reaction. Pd is considered as an alternative to Pt due to its high tolerance to poisoning and electronic similarity with Pt, which is a robust but expensive catalyst. However, its vulnerability to dissolving in acidic media prevents the use of Pd as an oxygen reduction reaction catalyst. In this study, a facile synthesis method was developed to prepare a carbon-encapsulated Pd catalyst using aniline. The oxidative polymerization of aniline with a Pd precursor formed Pd nanoparticles embedded in a rod-shaped polyaniline matrix. The polyaniline matrix was carbonized using heat treatment, which then acted as a source of N-containing carbon layer that protects Pd nanoparticles from dissolution and improves oxygen reduction reaction activity. The stability and oxygen reduction reaction activity of the synthesized Pd catalyst were strongly dependent on the heat treatment temperature. The Pd catalysts heat-treated at 300 °C and 500 °C exhibited improved activity and stability as compared to commercial Pd/C. We envision that this method is suitable for mass production of active and stable oxygen reduction reaction catalysts in proton exchange fuel cells.

An efficient synthesis of nitrogen and sulfur co-doped graphene-like carbon sheets from coir pith bio-waste through the mechanical activation method is reported in this study. The structural characterization reveals the presence of a graphene-like carbon sheet, which is uniformly doped with nitrogen and sulfur atoms in a carbon network. The nitrogen and sulfur co-doped graphene-like carbon sheets (NSG) has amorphous nature with a defective porous carbon structure and it depicts the maximum specific capacitance of 247.1 F g−1 at 0.2 A g−1 and a capacitance retention of 75.2% at 10 A g−1. The synthesized NSG-10 registered a maximum energy density of 33.6 Wh kg−1 at 0.2 A g−1 and shows the maximum power density of 4220.0 W kg−1 at 10.0 A g−1. Furthermore, a symmetric supercapacitor (SSC) device shows the device capacitance of 33.7 F g−1 at 0.2 A g−1 when operated at 1.0 V. The SSC device gives a capacitance retention of 82.0% at 10 A g−1 and reveals an excellent stability with no losses in capacitance with 100% columbic efficiency over 10,000 cycles. The results suggest that the proposed methodology is a simple and unique way to synthesize heteroatoms-doped graphene-like carbon sheets from biomass materials for a supercapacitor.

Performance of a polymer electrolyte membrane fuel cell with a Pd cathode catalyst was systemically investigated in this study. The Pd catalyst was directly formed on a gas diffusion layer by using electrodeposition (Pd/GDL). The electrodeposition formed aggregates of Pd nanoparticles on a gas diffusion layer with the preferred orientation of Pd(111) and Pd(200). In addition, the Pd aggregates mainly formed on the top surface of the gas diffusion layer. The membrane electrode assembly was fabricated with Pd/GDL as the cathode. The performance of the membrane electrode assembly was investigated by varying hot pressing parameters and back pressures, and the operating condition for the polymer electrolyte membrane fuel cell was optimized. Notably, introducing back pressure increased operating current density at 0.6 V by up to 45%. Durability of the membrane electrode assembly was also examined. Negligible deterioration of surface morphology of the Pd catalyst was observed even after accelerated stress testing, except for a slight increase in particle size. The results indicate that deterioration of the Pd cathode catalyst was not a major factor affecting overall single-cell performance degradation.