Water splitting is one of the ideal technologies to meet the ever increasing demands of energy. Many materials have aroused great attention in this field. The family of nickel-based sulfides is one of the examples that possesses interesting properties in water-splitting fields. In this paper, a controllable and simple strategy to synthesize nickel sulfides was proposed. First, we fabricated NiS hollow microspheres via a hydrothermal process. After a precise heat control in a specific atmosphere, NiS porous hollow microspheres were prepared. NiS was applied in hydrogen evolution reaction (HER) and shows a marvelous performance both in acid medium (an overpotential of 174 mV to achieve a current density of 10 mA/cm and the Tafel slope is only 63 mV/dec) and in alkaline medium (an overpotential of 148 mV to afford a current density of 10 mA/cm and the Tafel slope is 79 mV/dec). NiS was used in oxygen evolution reaction (OER) showing a low overpotential of 320 mV to deliver a current density of 10 mA/cm, which is meritorious. These results enlighten us to make an efficient water-splitting system, including NiS as HER catalyst in a cathode and NiS as OER catalyst in an anode. The system shows high activity and good stabilization. Specifically, it displays a stable current density of 10 mA/cm with the applying voltage of 1.58 V, which is a considerable electrolyzer for water splitting.

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In the past decade, fossil fuel resources have been exploited and utilized extensively, which could lead to increasing environmental crises, like greenhouse effect, water pollution, etc. Accordingly, many coping strategies have been put forward, such as water electrolysis, metalair batteries, fuel cell, etc. Among the strategies mentioned above, water electrolysis is one of the most promising. Water splitting, which can achieve sustainable hydrogen production, is a favorable strategy due to the abundance of water resources. Splitting of water includes two half reactions integral to its operation: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, its practical application is mainly impeded by the sluggish anode reaction. Simultaneously, noble metal oxides (IrO2 and RuO2) and Pt-based catalysts have been recognized as typical OER catalysts; however, the scarcity of noble metals greatly limits their development. Hence, designing an alternative electrocatalyst plays a vital role in the development of OER. However, exploring a highly active electrocatalyst for OER is still difficult. Herein, a miraculous construction of a tree-like array of NiS/Ni3S2 heterostructure, which is directly grown on Ni foam substrate, is synthesized via one-step hydrothermal process. Since NiS and Ni3S2 have shown great OER performance in previous investigations, this novel NiS-Ni3S2/Nikel foam (NF) heterostructure array has tremendous potential as a practical OER catalyst. Upon application in OER, the NiS-Ni3S2/NF heterostructure array catalyst exhibits excellent activity and stability. More specifically, this novel tree-like NiS-Ni3S2 heterostructure array shows extremely low overpotential (269 mV to achieve a current density of 10 mA•cm −2 ) and small Tafel slope for OER. It also shows extraordinary stability in alkaline electrolytes. Compared with the Ni3S2 nanorods array, the NiS-Ni3S2 heterostructure array has a synergistic effect that can improve the OER performance. Due to the secondary structure (Ni3S2 nanosheets), the tree-like NiS-Ni3S2 array provides more active sites could have higher specific surface area. The greater activity of the NiS/Ni3S2 heterostructure may also stem from the tight conjunction between tree-like NiS/Ni3S2 and the Ni foam substrate, which is beneficial for electronic transmission. Hydroxy groups can accumulate in large amounts on the surface of the tree-like array, and it also generates some Ni-based oxides that are favorable to OER. Moreover, the synergistic effect of such heterostructure can intrinsically improve the OER activity. The unique tree-like NiS-Ni3S2 heterostructure array has great potential as an alternative OER electrocatalyst.

Nanomaterials based on metals and their alloys have been paid increasing attention due to their adjustable morphology, high stability and excellent catalytic activity. In this work, Fritillaria cirrhosa-like Cu−Pd alloy nanoparticles were grown on carbon paper (Cu−Pd/CP) by one-step electrodeposition, serving as a self-supporting electrode to catalyze glucose oxidation. The morphological and structural characterizations of the Cu−Pd alloy were performed using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that Fritillaria cirrhosa-like Cu−Pd alloy nanoparticles with a size of about 600 nm were synthesized and uniformly distributed on CP. The 3D network structure composed of CP with good conductivity and Cu−Pd alloy nanoparticles with unique morphology greatly increased the specific surface area and conductivity of the material, which is beneficial to the electrocatalytic oxidation of glucose. As a self-supporting electrode, the prepared Cu−Pd/CP presented excellent electrocatalytic activity toward glucose oxidation with a wide linear range (0.003−10 mM), high sensitivity (2589 μA mM −1 cm −2 ), and low detection limit (1.3 μM). The proposed sensor has been successfully applied to the determination of glucose in real human serum samples, indicating that Cu−Pd/CP is a promising candidate for nonenzymatic glucose sensing.