Wen-Kun Gao

In situ sulfurized CoMoS/CoMoO4 shell–core nanorods supported on N-doped reduced graphene oxide (NRGO) as efficient electrocatalyst for hydrogen evolution reaction

Many strategies, such as doping metal, designing low-dimensional nanostructures, and enhancing the utilization of active sites based on a conductive support, have been intensively pursued to improve the intrinsic activity of transition metal chalcogenides for the hydrogen evolution reaction (HER). However, integrating all the above-mentioned merits into one electrocatalyst is still a significant challenge. Herein, we have successfully prepared uniform CoMoS/CoMoO4 (CMS) shell–core nanorods, with a diameter of 60 nm and a length of 800 nm, supported on N-doped reduced graphene oxide (NRGO). The obtained CMS/NRGO can combine many advantages, including transition metal doping, one-dimensional nanorods, and the superior conductivity of NRGO, resulting in very promising HER properties and excellent stability. The optimum sulfurization temperature for unsupported CMS nanorods has been explored using uniform CoMoO4 nanorods as a precursor. Although CMS-3 prepared with a sulfurization temperature of 300 °C has been found to possess the optimum activity for the HER, when adopting NRGO as a support, CMS-3/NRGO exhibits an impressive enhancement in HER performances with a low overpotential of 80 mV, a small Tafel slope of 58 mV dec−1, and a large exchange current density of 428 μA cm−2. In addition, the electrocatalytic activity of CMS-3/NRGO shows a negligible delay after 1000 cycles, indicating its robust electrochemical stability in acid electrolyte solution. Therefore, adopting low-temperature sulfurization of one-dimensional metal oxide precursors supported on NRGO may be a promising strategy for obtaining excellent electrocatalysts for the HER.

Coupling Ag-doping and rich oxygen vacancies in mesoporous NiCoO nanorods supported on nickel foam for highly efficient oxygen evolution

A crucial challenge still remains in the development of efficient and stable electrocatalysts for oxygen evolution reaction (OER) with desirable conductivity, a high surface area and rich oxygen vacancies. Herein, a type of Ag-doped mesoporous NiCoO nanorod with rich oxygen vacancies (NiCoO@Ag40/NF-Ar) for OER is prepared via an electrodeposition-hydrothermal reaction and the subsequent annealing treatment process under an Ar atmosphere. The electrodeposited Ag film is found to direct the uniform growth of the nanowire arrays of NiCo hydroxide precursors compared to the nanoparticles of NiCo hydroxide in the absence of the Ag film. Interestingly, the addition of C2H8N2 (EN) during the electrodeposition of the Ag film and the subsequent calcination under an Ar atmosphere collectively contribute to the formation of mesoporous nanorod structures and rich oxygen vacancies. The calcined NiCoO in air mainly have the Co3O4 phase, implying that it has fewer oxygen vacancies and weak activity for OER. The high surface area and one-dimensional feature of mesoporous nanorods are responsible for the increased exposure of active sites and fast charge transport behavior. Moreover, Ag doping can also improve the conductivity of NiCoO nanorods. NiCoO@Ag40/NF-Ar exhibits a highly efficient activity for OER with a current density of 140 mA cm−2 at an overpotential of 370 mV and a remarkable stability. The suitable Ar annealing treatment coupling Ag films and oxygen vacancies into transition metal oxide precursors may be a facile and promising method for constructing mesoporous nanostructures with rich oxygen vacancies for efficient water oxidation.

Nitrogen, phosphorus dual-doped molybdenum- carbide/molybdenum-phosphide-@-carbon nanospheres for efficient hydrogen evolution over the whole pH range

MoO42-@aniline-pyrrole (MoO42-@polymer) spheres as precursors have been used to synthesize unique core-shell nanostructure consisting of molybdenum carbide and molybdenum phosphide composites encapsulated into uniformly dual N, P-doped carbon shells (Mo2C/MoP@NPC) through a facile two-step strategy. Firstly, porous core-shell N-doped Mo2C@C (Mo2C@NC) nanospheres have been synthesized with ultrafine Mo2C nanoparticles as core and ultrathin NC as shell by a annealing route. Secondly, Mo2C/MoP@NPC has been obtained maintaining intact spherical-like morphology through a phosphidation reaction in high temperature. The synergistic effect of Mo2C and MoP may reduce the strong MoH bonding energy of pure Mo2C and provide a fast hydrogen release process. In addition, the dual N, P-doped carbon matrix as shell can not only improve the electroconductivity of catalysts but also prevent the corrosion of Mo2C/MoP nanoparticles during the electrocatalytic process. When used as HER cathode in acids, the resulting Mo2C/MoP@NPC shows excellent catalytic activity and durability, which only needs an overpotential of 160 mV to drive 10 mA cm-2. Moreover, it also exhibits better HER performance in basic and neutral media with the need for overpotentials of only 169 and 228 mV to achieve 10 mA cm-2, respectively. This inorganic-organic combination of Mo-based catalysts may open up a new way for water-splitting to produce large-scale hydrogen.

Hydrogen Evolution Activity of Ruthenium Phosphides Encapsulated in Nitrogen‐ and Phosphorous‐Codoped Hollow Carbon Nanospheres

RuPx nanoparticles (NPs) encapsulated in uniform N,P-codoped hollow carbon nanospheres (RuPx @NPC) have been synthesized through a facile route in which aniline-pyrrole copolymer nanospheres are used to disperse Ru ions followed by a gas phosphorization process. The as-prepared RuPx @NPC exhibits a uniform core-shell hollow nanospherical structure with RuPx NPs as the core and N,P-codoped carbon (NPC) as the shell. This strategy integrates many advantages of hollow nanostructures, which provide a conductive substrate and the doping of a nonmetal element. At high temperatures, the obtained thin NPC shell can not only protect the highly active phase of RuPx NPs from aggregation and corrosion in the electrolyte but also allows variation in the electronic structures to improve the charge-transfer rate greatly by N,P codoping. The optimized RuPx @NPC sample at 900 °C exhibits a Pt-like performance for the hydrogen evolution reaction (HER) and long-term durability in acidic, alkaline, and neutral solutions. The reaction requires a small overpotential of only 51, 74, and 110 mV at 10 mA cm-2 in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m phosphate-buffered saline, respectively. This work provides a new way to design unique phosphide-doped carbon heterostructures through an inorganic-organic hybrid method as excellent electrocatalysts for HER.