Characteristic examples of three types of change of form of p n relationships at 2 5 T , as the contents of elements alloying with palladium a r e gradually increased (4,37,70,74-83,95-98,~04,108,153,154), are illustrated in Figure 9. As for the palladiumhydrogen system itself (4), such relationships have been determined from direct equilibrations with hydrogen gas, as well as being derived from measurements of electrode potential. Similarly as for palladium-hydrogen, temperature dependences of the p n relationships have been used to supplement calorimetric data ( I 10) in deriving heats and cntropies of hydrogen absorption, both at initially low values (79)(80)(81)(82)95,100,108) of hydrogen content (n-to) and over (Y =p transition regionsThe sequence of relationships in Figure 9(c) (4,37,70,74-83,'04,I54,I78).shows gradual increases with increasing rhodium content in the range o f n over which (Y and / J ' phases coexist. This sequence now seems unique to the palladium-rhodium-hydrogen system (45,75, I 53,154), since some suggestions of similarities of the palladium-manganesehydrogen system (179) seem doubtful in view of possible incomplete equilibrations.'The remaining families of p n isotherms for palladium alloy-hydrogen systems would thus seem to be divisible into two groups represented by those in Figures 9(a) and 9 (b). In both cases the ranges of n over t i + p phase regions are successively shortened with increasing content of the alloying element, even in the cases of alloys with readily hydride-forming transition or inner transition elements such as vanadium Decreases, in the range of n over (r +/I regions, with increasing amounts of alloying elements, have continued to be deduced from X-ray determinations of and / 3 phase lattice constants for additional palladium alloyhydrogen systems (4,79-82,157, I 80-1 82).Apart from the probable case of the palladium-nickel-hydrogen system (so), these general trends of decreasing extents of ( Y , p coexistence with increasing contents of alloying element are similar to the effects of increasing temperature in the palladium-hydrogen system, being accompanied by decreases in the extents of hystereses of absorption and desorption relationships between hydrogen contents and other experimental parameters (4,69,(96)(97)(98) later, has importance in choices of alloy compositions as hydrogen permeation membranes. In addition to the arguments concerning the solubility of hydrogen in the palladium-silver alloys, the extents of decreases of hydrogen solubilities with increasing contents of other alloying metals have been used (95,104,108) in support of an essentially protonic nature of the hydrogen entities. However, in order to allow for proposed levels of electron donation it has seemed necessary to postulate adoptions of oxidation states by the alloying elements which can be difficult to reconcile with their relative positions in sequence of electronegaiivities.Moreover as for the palladium-hydrogen system, latterly there has been increasing emphasis on the account ...

Efficient separation of photogenerated electrons and holes, and associated surface reactions, is a crucial aspect of efficient semiconductor photocatalytic systems employed for photocatalytic hydrogen production. A new CoO /TiO /Pt photocatalyst produced by template-assisted atomic layer deposition is reported for photocatalytic hydrogen production on Pt and CoO dual cocatalysts. Pt nanoclusters acting as electron collectors and active sites for the reduction reaction are deposited on the inner surface of porous TiO nanotubes, while CoO nanoclusters acting as hole collectors and active sites for oxidation reaction are deposited on the outer surface of porous TiO nanotubes. A CoO /TiO /Pt photocatalyst, comprising ultra-low concentrations of noble Pt (0.046 wt %) and CoO (0.019 wt %) deposited simultaneously with one atomic layer deposition cycle, achieves remarkably high photocatalytic efficiency (275.9 μmol h ), which is nearly five times as high as that of pristine TiO nanotubes (56.5 μmol h ). The highly dispersed Pt and CoO nanoclusters, porous structure of TiO nanotubes with large specific surface area, and the synergetic effect of the spatially separated Pt and CoO dual cocatalysts contribute to the excellent photocatalytic activity.

Highy crystalline NiO nanoparticles are uniformly grown on the walls of carbon nanotubes (CNTs) by atomic layer deposition (ALD) at moderate temperature.Their size and stoichiometry are controlled by the ALD process parameters. The obtained NiO/CNT hybrids exhibit excellent performance in the electro-oxidation of methanol.

Two-dimensional (2D) molybdenum sulfide (MoS 2 ) is an attractive noble-metal-free electrocatalyst for hydrogen evolution (HER) in acids. Tremendous effort has been made to engineer MoS 2 catalysts with either more active sites or higher conductivity to enhance their HER activity. However, little attention has been paid to synergistically structural and electronic modulations of MoS 2 . Herein, 2D hydrogenated graphene (HG) is introduced into MoS 2 ultrathin nanosheets for the construction of a highly efficient and stable catalyst for HER. Owing to synergistic modulations of both structural and electronic benefits to MoS 2 nanosheets via HG support, such a catalyst has improved conductivity, more accessible catalytic active sites, and moderate hydrogen adsorption energy. On the optimized MoS 2 /HG hybrid catalyst, HER occurs with an overpotential of 124 mV at 10 mA cm −2 , a Tafel slope of 41 mV dec −1 , and a stable durability for 24 h continuous operation at 30 mA cm −2 without observable fading. The high performance of the optimized MoS 2 /HG hybrid catalyst for HER was interpreted with density functional theory calculations. The simulation results reveal that the introduction of HG modulates the electronic structure of MoS 2 to increase the number of active sites and simultaneously optimizes the hydrogen adsorption energy at S-edge atoms, eventually promoting HER activity. This study thus provides a strategy to design and develop high-performance HER electrocatalysts by employing different 2D materials.