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The electrocatalytic production of hydrogen peroxide (H 2 O 2 ) through the two-electron oxygen reduction reaction (ORR) requires costeffective catalysts with high selectivity, activity, and stability. Herein we report the synthesis and electrocatalytic assessment of nickel−nitrogen−carbon (Ni−N−C) electrocatalysts to gain insight into ORR activity and selectivity toward the production of H 2 O 2 . The activity and selectivity of the catalysts depended on the amount of nickel added during synthesis as well as the pH of the electrolyte. The materials were found to be heterogeneous in nature, consisting of nitrogen-doped carbon structures containing Ni species, including Ni 3 S 2 and covered metallic Ni particles. The presence of Ni during synthesis was imperative for the ORR performance in acidic electrolytes but had minimal impact on the performance in alkaline electrolytes. By experimentally demonstrating that Ni 3 S 2 , metallic Ni, and N-doped carbon species were not the source of activity, we postulate that atomically dispersed Ni−N x /C sites are responsible for the ORR performance in acidic electrolytes, with an activity of −0.3 mA cm −2 and a H 2 O 2 selectivity of 43% measured for the best Ni−N−C catalyst at 0.5 V vs RHE. This work highlights the potential and generates scientific insight into Ni− N−C catalysts to guide the design of improved performance metal−nitrogen−carbon catalysts based on inexpensive precursors and simplistic syntheses.

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The electrochemical supercapacitor performance of MnO2 is significantly influenced by the phase structure due to the various structural features of the different MnO2 polymorphs that include tunnels or layered structures that can facilitate ion transport and intercalation. However, the effect of the crystal structure of MnO2 within MnO2/carbon composites has not been fully explored or understood. Herein, we have synthesized different crystal structures of MnO2 (α- and β-MnO2) within MnO2/reduced graphene oxide (rGO) composites by a hydrothermal process using various amounts of (NH4)2SO4, followed by systematic structural characterization and electrochemical capacitance measurements. An excellent capacitance performance of 403 F g–1 was observed in α-MnO2/sulfur and nitrogen codoped reduced graphene oxide (S,N-rGO) composites because of the interconnection between the conductive porous 3D architectures of S,N-rGO and the α-MnO2 nanorods. This work highlights how the morphology, phase structure, and mass loading of MnO2 within MnO2/rGO composites directly influence the capacitance performance and rate capabilities, which provides insight into the design of MnO2-based composite materials for supercapacitor applications.

Bimetallic iron−copper nanoparticles (Fe/Cu-NPs) were synthesized by a single-pot surfactant-free method in aqueous solution [via the reduction of ferrous ion to zerovalent iron nanoparticles (Fe-NPs) and the subsequent copper-coating by metal ion exchange]. The produced Fe/Cu-NPs formed aggregates of spherical nanoparticles (approximately 30−70 nm) of Fe−Cu core−shell structures with 11 wt % copper content. The microbicidal effects of Fe/Cu-NPs were explored on Escherichia coli and MS2 coliphage, surrogates for bacterial and viral pathogens, respectively. Fe/Cu-NPs exhibited synergistically enhanced activity for the inactivation of E. coli and MS2, compared to single-metal nanoparticles (i.e., Fe-NPs and Cu-NPs). Various experiments (microbial inactivation tests under different conditions, fluorescence staining assays, experiments using ELISA and qRT-PCR, etc.) suggested that Fe/Cu-NPs inactivate E. coli and MS2 via dual microbicidal mechanisms. Two biocidal copper species [Cu(I) and Cu(III)] can be generated by different redox reactions of Fe/Cu-NPs. It is suggested that E. coli is strongly influenced by the cytotoxicity of Cu(I), while MS2 is inactivated mainly due to the oxidative damages of protein capsid and RNA by Cu(III).