In this study, a general and effective phosphorization strategy is successfully demonstrated to enhance supercapacitor performance of various transition metals oxide or hydroxide, such as Ni(OH) 2 , Co(OH) 2 , MnO 2 , and Fe 2 O 3 . For example, a 3D networked Ni 2 P nanosheets array via a facile phosphorization reaction of Ni(OH) 2 nanosheets is grown on the surface of a Ni foam. The Ni foam-supported Ni 2 P nanosheet (Ni 2 P NS/NF) electrode shows a remarkable specifi c capacitance of 2141 F g −1 at a scan rate of 50 mV s −1 and remains as high as 1109 F g −1 even at the current density of 83.3 A g −1 . The specifi c capacitance is much larger than those of Ni(OH) 2 NS/NF (747 F g −1 at 50 mV s −1 ). Furthermore, the electrode retains a high specifi c capacitance of 1437 F g −1 even after 5000 cycles at a current density of 10 A g −1 , in sharp contrast with only 403 F g −1 of Ni(OH) 2 NS/NF at the same current density. The similar enhanced performance is observed for Ni 2 P powder, which eliminates the infl uence of nickel foam. The enhanced supercapacitor performances are attributed to the 3D porous nanosheets network, enhanced conductivity, and two active components of Ni 2+ and P δ − with rich valences of Ni 2 P.

Probing competent electrocatalysts for hydrogen evolution reaction (HER) of water splitting is one of the most hopeful approaches to confront the energy and environmental crisis. Herein, we highlight ultrathin N-doped MoC nanosheets (N-MoC NSs) in the role of greatly efficient platinum-free-based electrocatalysts for the HER. The transformation of crystal phase and structure between MoO nanosheets with a thickness of ∼1.1 nm and N-MoC NSs with a thickness of ∼1.0 nm is studied in detail. Structural analyses make clear that the surfaces of the N-MoC NSs are absolutely encompassed by apical Mo atoms, hence affording an ideal catalyst prototype to expose the role of Mo atoms for the duration of HER catalysis. Theoretical calculations demonstrate that the nanosheet structure, N doping, and particular crystalline phase of MoC produce more exposed Mo active sites, including Mo atoms on the C plane and doped N atoms. Through detailed electrochemical investigations, N-MoC NSs possess HER activity with an onset potential of -48.3 mV vs RHE, Tafel slope of 44.5 mV dec, and overpotential of 99 mV vs RHE at the cathodic current density of 10 mA cm with excellent long-term stability. Lastly, the calcination temperature and dicyandiamide amount can obviously affect the phase transformation and surface structure of molybdenum carbide, resulting in an adjustable HER activity. This synthesis mechanism will facilitate the understanding and optimization of Mo-based electrocatalysts in the energy conversion field.

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Biomass-derived nitrogen self-doped porous carbon was synthesized by a facile procedure based on simple pyrolysis of water hyacinth (eichhornia crassipes) at controlled temperatures (600-800 °C) with ZnCl2 as an activation reagent. The obtained porous carbon exhibited a BET surface area up to 950.6 m(2) g(-1), and various forms of nitrogen (pyridinic, pyrrolic and graphitic) were found to be incorporated into the carbon molecular skeleton. Electrochemical measurements showed that the nitrogen self-doped carbons possessed a high electrocatalytic activity for ORR in alkaline media that was highly comparable to that of commercial 20% Pt/C catalysts. Experimentally, the best performance was identified with the sample prepared at 700 °C, with the onset potential at ca. +0.98 V vs. RHE, that possessed the highest concentrations of pyridinic and graphitic nitrogens among the series. Moreover, the porous carbon catalysts showed excellent long-term stability and much enhanced methanol tolerance, as compared to commercial Pt/C. The performance was also markedly better than or at least comparable to the leading results in the literature based on biomass-derived carbon catalysts for ORR. The results suggested a promising route based on economical and sustainable biomass towards the development and engineering of value-added carbon materials as effective metal-free cathode catalysts for alkaline fuel cells.

Development of non-noble-metal catalysts for hydrogen evolution reaction (HER) with both excellent activity and robust stability has remained a key challenge in the past decades. Herein, for the first time, N-doped carbon-wrapped cobalt nanoparticles supported on N-doped graphene nanosheets were prepared by a facile solvothermal procedure and subsequent calcination at controlled temperatures. The electrocatalytic activity for HER was examined in 0.5 M H2SO4. Electrochemical measurements showed a small overpotential of only −49 mV with a Tafel slope of 79.3 mV/dec. Theoretical calculations based on density functional theory showed that the catalytically active sites were due to carbon atoms promoted by the entrapped cobalt nanoparticles. The results may offer a new methodology for the preparation of effective catalysts for water splitting technology.

Advanced materials for electrocatalytic water splitting are central to renewable energy research. In this work, three-dimensional (3D) hierarchical frameworks based on the self-assembly of MoS2 nanosheets on graphene oxide were produced via a simple one-step hydrothermal process. The structures of the resulting 3D frameworks were characterized by using a variety of microscopic and spectroscopic tools, including scanning and transmission electron microscopies, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman scattering. Importantly, the three-dimensional MoS2/graphene frameworks might be used directly as working electrodes which exhibited apparent and stable electrocatalytic activity in hydrogen evolution reaction (HER), as manifested by a large cathodic current density with a small overpotential of -107 mV (-121 mV when loaded on a glassy-carbon electrode) and a Tafel slope of 86.3 mV/dec (46.3 mV/dec when loaded on a glassy-carbon electrode). The remarkable performance might be ascribed to the good mechanical strength and high electrical conductivity of the 3D frameworks for fast charge transport and collection, where graphene oxide provided abundant nucleation sites for MoS2 deposition and oxygen incorporation led to the formation of defect-rich MoS2 nanosheets with active sites for HER.

Advanced materials for electrocatalytic water splitting are central to renewable energy research. In this work, MoS2 nanosheets supported on porous metallic MoO2 (MoS2/MoO2) were produced by sulfuration treatments of porous and highly conductive MoO2 for the hydrogen evolution reaction. Porous MoO2 with one-dimensional channel-like structures was prepared by calcination at elevated temperatures using phosphomolybdic acid as the precursor and mesoporous silica (SBA-15) as the template, and the subsequent hydrothermal treatment in the presence of thioacetamide led to the transformation of the top layers to MoS2 forming MoS2/MoO2 composites. Electrochemical studies showed that the obtained composites exhibited excellent electrocatalytic activity for HER with an onset potential of -104 mV (vs. RHE), a large current density (10 mA cm(-2) at -0.24 V), a small Tafel slope of 76.1 mV dec(-1) and robust electrochemical durability. The performance might be ascribed to the high electrical conductivity and porous structures of MoO2 with one-dimensional channels of 3 to 4 nm in diameter that allowed for fast charge transport and collection.

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