Highly-dispersed 2D NiFeP/CoP heterojunction trifunctional catalyst for efficient electrolysis of water and urea.

The electrocatalytic production of "green hydrogen", such as through the electrolysis of water or urea has been vigorously advocated to alleviate the energy crisis. However, their electrode reactions including oxygen evolution reaction (OER), urea oxidation reaction (UOR), and hydrogen evolution reaction (HER) all suffer from sluggish kinetics, which urgently need catalysts to accelerate the processes. Herein, we design and prepare an OER/UOR/HER trifunctional catalyst by transforming the homemade CoO nanorod into a two-dimensional (2D) ultrathin heterojunction nickel-iron-cobalt hybrid phosphides nanosheet (NiFeP/CoP) via a hydrothermal-phosphorization method. Consequently, a strong electronic interaction was found among the Ni2P/FeP4/CoP heterogeneous interfaces, which regulates the electronic structure. Besides the high mass transfer property of 2D nanosheet, Ni2P/FeP4/CoP displays improved OER/UOR/HER performance. At 10 mA cm-2, the OER overpotential reaches 274 mV in 1.0 M KOH, and the potential of UOR is only 1.389 V in 1.0 M KOH and 0.33 M urea. More strikingly, the two-electrode systems for electrolysis water and urea-assisted electrolysis water assembled by NiFeP/CoP could maintain long-term stability for 35 h and 12 h, respectively. This work may help to pave the way for upcoming research horizons of multifunctional electrocatalysts.

Synergistic Effect of N-NiMoO4 /Ni Heterogeneous Interface with Oxygen Vacancies in N-NiMoO4 /Ni/CNTs for Superior Overall Water Splitting.

The exploring of economical, high-efficiency, and stable bifunctional catalysts for hydrogen evolution and oxygen evolution reactions (HER/OER) is highly imperative for the development of electrolytic water. Herein, a 3D cross-linked carbon nanotube supported oxygen vacancy (Vo )-rich N-NiMoO4 /Ni heterostructure bifunctional water splitting catalyst (N-NiMoO4 /Ni/CNTs) is synthesized by hydrothermal-H2 calcination method. Physical characterization confirms that Vo -rich N-NiMoO4 /Ni nanoparticles with an average size of ≈19 nm are secondary aggregated on CNTs that form a hierarchical porous structure. The formation of Ni and NiMoO4 heterojunctions modify the electronic structure of N-NiMoO4 /Ni/CNTs. Benefiting from these properties, N-NiMoO4 /Ni/CNTs drives an impressive HER overpotential of only 46 mV and OER overpotential of 330 mV at 10 mA cm-2 , which also shows exceptional cycling stability, respectively. Furthermore, the as-assembled N-NiMoO4 /Ni/CNTs||N-NiMoO4 /Ni/CNTs electrolyzer reaches a cell voltage of 1.64 V at 10 mA cm-2 in alkaline solution. Operando Raman analysis reveals that surface reconstruction is essential for the improved catalytic activity. Density functional theory (DFT) calculations further demonstrate that the enhanced HER/OER performance should be attributed to the synergistic effect of Vo and heteostructure that improve the conductivity of N-NiMoO4 /Ni/CNTs and facilitatethe desorption of reaction intermediates.

FeNi Alloy Nanoparticles Encapsulated in Carbon Shells Supported on N-Doped Graphene-Like Carbon as Efficient and Stable Bifunctional Oxygen Electrocatalysts.

The development of cost-effective and durable oxygen electrocatalysts remains highly critical but challenging for energy conversion and storage devices. Herein, a novel FeNi alloy nanoparticle core encapsulated in carbon shells supported on a N-enriched graphene-like carbon matrix (denoted as FeNi@C/NG) was constructed by facile pyrolyzing the mixture of metal salts, glucose, and dicyandiamide. The in situ pyrolysis of dicyandiamide in the presence of glucose plays a significant effect on the fabrication of the porous FeNi@C/NG with a high content of doped N and large specific surface area. The optimized FeNi@C/NG catalyst displays not only a superior catalytic performance for the oxygen reduction reaction (ORR, with an onset potential of 1.0 V and half-wave potential of 0.84 V) and oxygen evolution reaction (OER, the potential at 10 mA cm-2 is 1.66 V) simultaneously in alkaline, but also outstanding long-term cycling durability. The excellent bifunctional ORR/OER electrocatalytic performance is ascribed to the synergism of the carbon shell and FeNi alloy core together with the high-content of nitrogen doped on the large specific surface area graphene-like carbon.

N/S/B-doped graphitized carbon encased Fe species as a highly active and durable catalyst towards oxygen reduction reaction.

Exploring cost-effective, high-performance and durable non-precious metal catalysts is of great significance for the acceleration of sluggish oxygen reduction reaction (ORR). Here, we report an intriguing heteroatom-doped graphitized carbon encased Fe species composite by introducing N, S and B sequentially. The experimental approach was designed ingeniously for that the FeCl3·6H2O could catalyze thiourea to synthesize N, S co-doped carbon materials which would further react with H3BO3 and NH3 (emerged at the heat-treatment process) to prepare N, S and B co-doped carbon materials (Fe-N/S/B-C). The Fe-N/S/B-C exhibits an impressive ORR activity for its half-wave potential of -0.1 V, which is 36 mV or 19 mV higher than that of the corresponding single or dual doped counterparts (Fe-N-C or Fe-N/S-C) and 31 mV positive than that of Pt/C catalyst, respectively. Further chronoamperometric measurement and accelerated aging test confirm the excellent electrochemical durability of Fe-N/S/B-C with the stable core-shell structure. The remarkable ORR performance and facile preparation method enable Fe-N/S/B-C as a potential candidate in electrochemical energy devices.

Efficient Synthesis of Nitrogen- and Sulfur-co-Doped Ketjenblack with a Single-Source Precursor for Enhancing Oxygen Reduction Reaction Activity.

Promoting the oxygen reduction reaction (ORR) catalytic activities of cost-effective catalysts is of great significance for the development of various energy conversion and storage systems. Herein, we describe the preparation of a highly active N- and S-co-doped ketjenblack (Kb) by facile pyrolysis of a mixture of thiourea and Kb in the presence of FeCl3 ⋅6 H2 O followed by an acid-leaching process. This novel synthetic approach was rationally designed with the consideration that thiourea could easily introduce both N and S heteroatoms into the carbon matrix by a heat-treatment method by releasing plentiful reactive N- and S-containing gases, which could simultaneously optimize the porous structure of the resultant catalyst. Physical characterization revealed that N and S were homogeneously incorporated into the nanostructure of Kb and formed a hierarchical porous structure with a high specific surface area. The N/S-Kb catalyst showed impressive ORR activity, with an onset potential of 0.08 V at 0.1 mA cm-2 , which is 20 mV more positive than that of commercial 20 wt. % Pt/C catalyst. This was coupled with long-term durability and superior methanol tolerance in alkaline media. The improved ORR performance can be mainly ascribed to synergistic contributions of highly efficient active sites arising from high contents of thiophene S and pyridinic N along with the high specific surface area and the favorable mass-transport properties arising from the hierarchical porous structure. The remarkable ORR performance and facile preparation method make the N/S-Kb catalyst a promising substitute for Pt in electrochemical energy devices.