A nanoflower-like polypyrrole-based cobalt-nickel sulfide hybrid heterostructures with electrons migration to boost overall water splitting

Nickel molybdate/cobalt iron carbonate hydroxide heterojunction with oxygen vacancy enables interfacial synergism to trigger oxygen evolution reaction

The development of electrocatalysts with excellent performance toward oxygen evolution reaction (OER) for the production of hydrogen is of great significance to alleviate energy crisis and environmental pollution. Herein, the heterostructure (NMO/FCHC-0.4) was fabricated by the coupling growth of NiMoO4 (NMO) and cobalt iron carbonate hydroxide (FCHC) on nickel foam as an electrocatalyst for OER. The interfacial synergy on NMO/FCHC-0.4 heterojunction can promote the interfacial electron redistribution, affect the center position of d band, optimize the adsorption of intermediate, and improve the conductivity. Beyond, oxygen defect sites are conducive to the adsorption of intermediates, and increase the number of active sites. Real-time OER kinetic simulation revealed that the interfacial synergism and molybdate could reduce the adsorption of hydroxide, promote the deprotonation step of M-OH, and facilitate the formation of M-OOH (M represents the metal active site). As a result, NMO/FCHC-0.4 displays excellent OER electrocatalytic performance with an overpotential of 250/280 mV at the current density 100/200 mA cm-2 and robust stability at 100 mA cm-2 for 100 h. This work provides deep insights into the roles of interfacial electronic modulation and oxygen vacancy to design high-efficiency electrocatalysts for OER.

Conducting and Magnetic Hybrid Polypyrrole/Nickel Composites and Their Application in Magnetorheology

Hybrid organic/inorganic conducting and magnetic composites of core-shell type have been prepared by in-situ coating of nickel microparticles with polypyrrole. Three series of syntheses have been made. In the first, pyrrole was oxidised with ammonium peroxydisulfate in water in the presence of various amounts of nickel and the composites contained up to 83 wt% of this metal. The second series used 0.1 M sulfuric acid as a reaction medium. Finally, the composites with polypyrrole nanotubes were prepared in water in the presence of structure-guiding methyl orange dye. The nanotubes have always been accompanied by the globular morphology. FTIR and Raman spectroscopies confirmed the formation of polypyrrole. The resistivity of composite powders of the order of tens to hundreds Ω cm was monitored as a function of pressure up to 10 MPa. The resistivity of composites slightly increased with increasing content of nickel. This apparent paradox is explained by the coating of nickel particles with polypyrrole, which prevents their contact and subsequent generation of metallic conducting pathways. Electrical properties were practically independent of the way of composite preparation or nickel content and were controlled by the polypyrrole phase. On the contrary, magnetic properties were determined exclusively by nickel content. The composites were used as a solid phase to prepare a magnetorheological fluid. The test showed better performance when compared with a different nickel system reported earlier.

Bulk CrCoNiFe alloy with high conductivity and density of grain boundaries for oxygen evolution reaction and urea oxidation reaction

Multiple-principal-element alloys (MPEAs) with maximized configurational entropy show high catalytic activities for oxygen evolution reaction (OER) and urea oxidation reaction (UOR). However, the accurate relationship between their complex components (i.e., elements, phase structure, grain boundary density) and intrinsic catalytic activity is still unclear. Herein, a series of bulk MPEAs with face-centered cubic (FCC) phase structures were fabricated by the arc-melting method under an argon atmosphere. Compared to the CrCoNi and CrCoNiFeMn, the CrCoNiFe affords a higher UOR performance with the lowest overpotential of 331 mV at 10 mA·cm^-2 in 1 M KOH with 0.33 M urea, due to excellent conductivity and high density of grain boundaries. The urea electrolyzer using CrCoNiFe as anode and Pt as cathode shows a low voltage of 1.622 V at 10 mA cm^-2 and long-term stability of 60 h at 20 mA cm^-2 (4.08% decrease). These findings offer a facile strategy for designing bulk MPEAs electrodes for energy conversion.

Mild construction of an Fe-B-O based flexible electrode toward highly efficient alkaline simulated seawater splitting

It is essential to construct self-supporting electrodes based on earth-abundant iron borides in a mild and economical manner for grid-scale hydrogen production. Herein, a series of highly efficient, flexible, robust, and scalable Fe-B-O@FeB_x modified on hydrophilic cloth (denoted as Fe-B-O@FeB_x/HC, 10 cm × 10 cm) are fabricated by mild electroless plating. The overpotentials and Tafel slope values for the hydrogen and oxygen evolution reactions are 59 mV and 57.62 mV dec^-1 and 181 mV and 65.44 mV dec^-1, respectively; only 1.462 V is required to achieve 10 mA cm^-2 during overall water splitting (OWS). Fe-B-O@FeB_x/HC maintains its high catalytic activity for more than 7 days at an industrial current density (400 mA cm^-2), owing to the loosened popcorn-like Fe-B-O@FeB_x that is firmly loaded on a 2D-layered and mechanically robust substrate along with its fast charge and mass transfer kinetics. The chimney effect of core-shell borides@(oxyhydro)oxides enhances the OWS performance and protects the inner metal borides from further corrosion. Moreover, the flexible Fe-B-O@FeB_x/HC electrode has a low cost for grid-scale hydrogen production ($2.97 kg^-1). The proposed strategy lays a solid foundation for universal preparation, large-scale hydrogen production and practical applications thereof.