| Hydrogen seems to be the most likely fuel of the future, concerning about the issues of sustainability, environmental emissions and energy security. A clean and renewable method of hydrogen production is electrolysis of water using renewable energies, in particular solar energy. Fundamentally, the interconversion of water and hydrogen can also be considered as a possible solution to convert electrical energy into a storable, chemical form that in turn can be released upon an electricity shortage. Pt-group metals are the best catalysts for hydrogen production, unfortunately their scarcity and expensive price make them impractical for global-scale application, which creates a strong demand for developing cheap and abundant materials to reduce the cost of hydrogen generating technologies and ultimately enable a hydrogen economy. In addition, the existing methods for the preparation of hydrogen evolusion reaction(HER) electrodes are complicated. And their morphology is hard to control. What’s worse, the conventional electrodes exhibit a characteristic mud-cracked structure. Accordingly, designing nanostructured electrodes with high catalytic activity, high stability and low cost through simple and clean methods has important research significance and use value.①We report the development of an ethylene glycol(EG)-mediated hydrothermal method combined with a post annealing treatment to construct Ru O2-Ni O nanorod arrays onto Ni foam as a binder-free integrated electrode for the HER. EG coordinates with Ru Cl3 or Ni Cl2 to form metal alkoxide on Ni foam because of its coordination ability with transition metal ions, which serves as the nuclei for the subsequent oligomerization to further self-assembly into ordered nanorods. SEM images show that the interconnected coating of Ru O2-Ni O on Ni foam is composed of perpendicularly oriented nanorod arrays approximately 1-2 μm in length. The prepared electrode exhibits excellent HER performance and long-term stability. The onset potential of the Ru O2-Ni O/Ni foam electrode shifts significantly toward a positive direction(175 m V) relative to the Ni foam electrode. The surface area of Ru O2-Ni O/Ni is almost 15 and even 23 times larger than that of the Ni foam and Ni O/Ni foam electrodes. The exchange current density(j0) of the HER on Ru O2-Ni O/Ni foam is 2.24×10-3 A cm-2, which is about 2 orders of magnitude larger than that on Ni foam or Ni O/Ni foam electrodes; At an overpotential of η=100 m V, the charge transfer resistance Rct is only 0.50 Ω for the HER on the Ru O2-Ni O/Ni foam electrode, remarkably smaller than that on Ni foam(35.93 Ω) and Ni O/Ni foam(173.60 Ω), indicating that the Ru O2-Ni O/Ni foam electrode is more active for the HER. This impressive electrochemical performance is largely attributed to the material’s unique nanostructure. We conclude that the presence of nickel oxide/hydroxide on the surface of the catalyst promotes the dissociation of water and the formation of hydrogen intermediates that can then adsorb onto the nearby ruthenium species and recombine into molecular hydrogen at a very rapid rate. The hydrothermal method for directly growing electroactive nanostructured arrays on a conductive substrate offers a promising route for developing a new class of Ni-based high performance electrodes for the HER in practical applications②We develope a magnetron sputtering method for synthesizing vertical Ni-Mo alloy nanorods on the surface of Ni foam as a binder-free integrated catalyst for the HER. Ni-Mo alloy manifests the amorphous or microcrystalline structure, which is beneficial for the electrochemical desorption of Had; SEM image shows the surface of as-deposited Ni-Mo alloy film is composed of highly uniform nanoparticles, with a diameter of about 50 nm and the cross-sectional SEM image further reveals a definite morphology of vertically aligned nanorods structure, of which the length is about 1μm. The nanorods structure is favorable for quick removal of gas bubbles from the electrode surface, which could minimize the resistance of electrolyte diffusion to the electrode surface. The surface area of Ni-Mo/Ni foam is almost 5 times larger than that of Ni/Ni foam, which strongly indicates that Mo contributes substantially to the enlargement of the electrode effective surface area of nickel electrode and accordingly leads to an enhanced performance; At η=60 m V, the Rct value of Ni-Mo/Ni foam(1.59 Ω) is much smaller than that for Ni foam(65.86 Ω), Ni/Ni foam(13.03 Ω) and Mo/Ni foam(22.89 Ω), suggesting Ni-Mo/Ni foam is more active for the HER. Therefore the as-obtained Ni-Mo electrocatalyst presents excellent catalytic activity for the HER in the light of inosculating the merits of large active surface area provided by its unique nanorods structure, and high intrinsic activity benefited from the synergistic effect between Ni and Mo. More generally, this nanoscaled design of electrode architecture here provides a valuable strategy for catalyst development and should be applicable for other gas evolution catalytic materials. |
PDF Full Text Request