As substitutions for transition metal oxides (MOs), transition metal carbonates (MCO3) have been attracting more and more attention because of their lithium storage ability in recent years. Is MCO3 better than MOs for lithium storage? To answer this question, monodisperse CoCO3 and CoO microspindles with comparable structures were synthesized and investigated as a case study. Excluding its structural effect, we found CoCO3 still exhibited reversible capacities and rate capabilities much higher than those of CoO. The reversible capacity of CoCO3 after 10 cycles was 1065 mAh g(-1), 48.2% higher than that (∼720 mAh g(-1)) of CoO. Furthermore, the greatly different electrochemical behaviors were investigated by analyzing the discharge-charge profiles, cyclic voltammetry curves, and Nyquist plots in depth. This work can improve our understanding of the lithium storage advantages of MCO3 against MOs and enlighten us in terms of developing high-performance MCO3 with favorable structures.

A high-performance Ni 1Àx Fe x on polyethyleneimine (PEI)-functionalized molybdenum disulfide (MoS 2 ) electrocatalyst has been synthesized by an electroplating in situ growth approach. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the successful functionalization of MoS 2 with PEI. The empty orbitals of Ni 2+ and Fe 2+ (Ni and Fe precursors) coordinated with the donated lone pairs of nitrogen atoms in PEI-mediated MoS 2 and then the Ni 2+ and Fe 2+ were in situ reduced at a negative potential. Transmission electron microscope images and X-ray diffraction reveal that Ni 85 Fe 15 nanoparticles with an average size of 2.25 nm are uniformly dispersed on the PEI-MoS 2 sheets. The Ni 1Àx Fe x /PEI-MoS 2 catalyst exhibits unexpectedly high activity towards the hydrazine oxidation reaction, which can be attributed to highly homogeneous dispersed Ni 1Àx Fe x alloy. It also shows enhanced electrochemical stability due to the structural integrity of PEI-MoS 2 . Finally, the Ni 85 Fe 15 /PEI-MoS 2 catalyst is proved to be very valuable for applications in hydrazine fuel cells, as compared with Ni 90 Fe 10 / PANi-MoS 2 and Ni 85 Fe 15 /MoS 2 catalysts.

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A very efficient, in situ growth approach has been developed to fabricate a graphene oxide (GO)-supported, highperformance Ni 1−x Fe x loading electrocatalyst. Transition metal nanoparticles (NPs) such as Ni are quite attractive due to their advantages in cost, and excellent electrocatalytic activity for hydrazine electrooxidation. However, their strong aggregation propensity makes it difficult to develop them into highly efficient electrocatalysts.Polyethyleneimine (PEI), a branched polyelectrolyte, is devised to resolve this problem, and is utilized to uniformly anchor Ni-Fe NPs on GO. Meanwhile, partial GO can be reduced to reduced graphene oxide (rGO) in the presence of amine-containing molecules, which is favourable to enhance the electrical conductivity of supporting materials.Ni 1−x Fe x NPs (50% loading) are prepared by a co-reduction method of metal precursors with hydrazine hydrate under 100 °C for 3 h. The content of PEI attached on GO significantly affects the dispersion and size of the resulting Ni 1−x Fe x NPs. Transmission electron microscope (TEM) images reveal that the Ni 1−x Fe x NPs with an average size of 8 nm are homogeneously dispersed on PEI-rGO 10 : 1 sheet. The electrochemical measurements indicate that the Ni 1−x Fe x /PEI-rGO 10 : 1 hybrid with a Ni : Fe mass ratio of 80 : 20 exhibits the highest electrocatalytic activity toward hydrazine oxidation, while the PEI-rGO 10 : 1 supporting material plays an excellent role in the synergistic catalytic effect. Under the same conditions, the electrocatalytic activity of Ni 80 Fe 20 NPs on PEI-rGO 10 : 1 for hydrazine is 2 times higher than that of the Ni 80 Fe 20 NPs directly deposited on GO.

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