Identification of the active species in electrocatalysts toward hydrogen evolution reaction (HER) is of great significance for the development of the catalytic industry; however, it is still the subject of considerable controversy. Herein, we applied operando synchrotron X-ray powder diffraction (SXRD) in the NiSe 2 electrocatalyst system, and an in situ phase transformation from cubic NiSe 2 to hexagonal NiSe was revealed. The NiSe phase showed an enhanced catalytic activity. Operando Raman spectroscopy verified the decomposition of NiSe 2 during HER. Theoretical calculations suggested that the charge transfers from the Se site to Ni site during this evolution process, leading to an increased conductivity and a shifting up of d-band center, which is attributed to the enhanced activity. The generated NiSe phase acts as the "real" active species. Our work unravels the underlying phase transition of the electrocatalyst on reductive conditions in alkaline medium and highlights the significance of identifying the intrinsic active sites under realistic reaction conditions.

There has been an intense research to develop 2-H MoS2 based catalysts to reduce or eliminate the use of Pt/C at higher metal loading for hydrogen evolution reaction (HER) in catalytic hydrolysis of water, which enables the capture of renewable energy sources as fuel and chemical. However, the study of its uncommon polymorph, 1T-MoS2 and particularly the doping effect with transition metal (TM) is rather limited due to the instability of this phase. Here we report a simple ambient temperature modification method using sonication to dope the single layer 1T-S MoS2 with various TM precursors. It is found that 1-T S MoS2 is more superior than corresponding 2H-S MoS2 and the inclusion of 3 wt% Pt or Pd can also further enhance the HER activity. STEM-EELS and XAS show the active single TM atom doping on this surface is to account for the high activity. Kinetic and DFT analyses also illustrate that the metallic nature of 1T-S MoS2 greatly facilitates the first proton reduction step from water, rendering it non-rate limiting as contrast to that of 2H-S MoS2. The inclusion of TM single doper such as Pd, despite at low loading, can offer the dramatic acceleration on the rate limiting recombination of H to H2. As a result, a bifunctional catalysis for HER over this tailored composite structure is demonstrated which outperforms most reported catalysts in this area.

Vulcan carbon was pre-treated at 850 o C at a ramp rate of 5 o C/min and maintained for 24 hours under 5% H2 in Ar. Cs-Ru modified MgO and AC preparationTypically, Ru3(CO)12 was dispersed in THF for 2 hours under sonication. The mixture was then transferred to the MgO or activated carbon (AC) and allowed to sonicate at ambient

Transition metal-doped nickel phosphide nanoparticles with metallic properties are prepared by a simple and facile wet-chemical method. It is shown for the first time that these transition metals: iron, cobalt, manganese, and molybdenum, can atomically substitute nickel in the parent hcp phosphide lattice as a single phase without significant change in its metallic structure and morphology. They are employed as electro-and photocatalysts for hydrogen evolution reaction, which show highly tunable activities dependent on electron filling of their metallic bands and H coverage according to our experimental and theoretical rationalizations. Molybdenum-doped nickel phosphide nanoparticle with lower H coverage exhibits the best hydrogen evolution performance in electrocatalytic hydrogen evolution reaction, which also shows excellent photocatalytic hydrogen production with organic photosensitizer. In addition, cobalt-doped nickel phosphide nanoparticle with higher H coverage with aqueous photosensitizer gives more superior hydrogen evolution rate.

Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.

Foreign transition metals are doped into the hexagonal nickel phosphide structure through a simple and facile bottom-up wet-chemical synthesis process via stabilization with oleylamine, trioctylphosphine (TOP), and trioctylphosphine oxide (TOPO): the as-prepared transition metal-doped nickel phosphide nanoparticles show a high level of doping but create no significant distortion of the crystal structure and morphology against pristine nickel phosphide nanoparticles, which exhibit excellent activity in the electrochemical oxygen evolution reaction (OER), having overpotential as small as 330 mV at 20 mA cm with a low Tafel slope value of 39 mV dec.

No abstract

There has been a substantial research effort worldwide to develop non-noble metal catalysts in electrolysers for H2 production from renewable energy sources. Pt catalysts are found to display the highest hydrogen evolution reaction (HER) activity under typical experimental conditions with relatively low acidity and over-potentials. However, it is noted that catalytic activity is highly dependent on acidity and applied potential used. In real practice of a high workload electrolyser high acidity and large negative potentials are required to optimize the HER activity. We hereby report that inexpensive silver catalysts, particularly the cubic form of silver nanoparticles, can clearly exhibit superior HER activity over Pt with a different rate determining step in an electrolyser when such conditions are reached. This is attributed to the weaker Ag-H bond at the surface than Pt-H which is more favorable for H recombination to form H2. It is thus believed that this study provides new insights into designing economical and highly efficient catalysts that can replace the expensive noble metal analogues in a working electrolyser.