Monoatomic Platinum-Embedded Hexagonal Close-Packed Nickel Anisotropic Superstructures as Highly Efficient Hydrogen Evolution Catalyst.

The rational design of platinum (Pt) based nanostructures with specific crystal structure plays a significant role in their diverse applications. Herein, the anisotropic superstructures (ASs) of monoatomic Pt-embedded hexagonal close-packed nickel (hcp Ni) nanosheets were successfully synthesized for efficient hydrogen evolution in which an unusual dissociation-diffusion-desorption mechanism played a crucial role. The overpotential for the Pt/Ni ASs to reach the specific current density (10 mA cm-2) is 28.0 mV, which is much lower than that of conventional Pt/C catalyst (71.0 mV). Moreover, at the overpotential of 100 mV, the mass activity of 30.2 A mgPt-1 for the Pt/Ni ASs is 1060% greater than that in conventional Pt/C catalyst (2.6 A mgPt-1). This work provides a new approach to synthesize highly anisotropic superstructures embedded with monoatomic noble metals to boost their hopeful applications in catalytic applications.

Controllable CO adsorption determines ethylene and methane productions from CO2 electroreduction.

Among all CO2 electroreduction products, methane (CH4) and ethylene (C2H4) are two typical and valuable hydrocarbon products which are formed in two different pathways: hydrogenation and dimerization reactions of the same CO intermediate. Theoretical studies show that the adsorption configurations of CO intermediate determine the reaction pathways towards CH4/C2H4. However, it is challenging to experimentally control the CO adsorption configurations at the catalyst surface, and thus the hydrocarbon selectivity is still limited. Herein, we seek to synthesize two well-defined copper nanocatalysts with controllable surface structures. The two model catalysts exhibit a high hydrocarbon selectivity toward either CH4 (83%) or C2H4 (93%) under identical reduction conditions. Scanning transmission electron microscopy and X-ray absorption spectroscopy characterizations reveal the low-coordination Cu0 sites and local Cu0/Cu+ sites of the two catalysts, respectively. CO-temperature programed desorption, in-situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory studies unveil that the bridge-adsorbed CO (COB) on the low-coordination Cu0 sites is apt to be hydrogenated to CH4, whereas the bridge-adsorbed CO plus linear-adsorbed CO (COB + COL) on the local Cu0/Cu+ sites are apt to be coupled to C2H4. Our findings pave a new way to design catalysts with controllable CO adsorption configurations for high hydrocarbon product selectivity.

Surface-modulated palladium-nickel icosahedra as high-performance non-platinum oxygen reduction electrocatalysts.

The search for high-performance non-platinum (Pt) electrocatalysts is the most challenging issue for fuel cell technology. Creating bimetallic non-Pt nanocrystals (NCs) with core/shell structures or alloy features has widely been explored as the most effective way for enhancing their electrochemical properties but still suffered from undesirable performance due to the limited interactions between the different components. By addressing the above issue, we report on a new class of active and stable bimetallic non-Pt electrocatalysts with palladium (Pd) icosahedra as the core and nickel (Ni) decorating the surface toward cathodic oxygen reduction reaction (ORR) under alkaline conditions. The optimized Pd6Ni icosahedra with unique interaction between an icosahedral Pd core and surface Ni yield the highest ORR activity with a mass activity of 0.22 A mgPd-1, which is better than those of the conventional Pd6Ni icosahedra with alloy surfaces or Pd-rich surfaces, and even two times higher than that of the commercial Pt/C (0.11 A mgPt-1), representing one of the best non-Pt electrocatalysts. Simulations reveal that the Pd icosahedra decorated with Ni atoms emerged in the subsurface can weaken the interaction between the adsorbed oxygen and Pd (111) facet and enhance the ORR activities due to an obvious shift of d-band center. More significantly, under electrochemical accelerated durability test, the Pd6Ni icosahedra can endure at least 10,000 cycles with negligible activity decay and structural change. The present work demonstrates an important advance in surface tuning of bimetallic NCs as high-performance non-Pt catalysts for catalysis, energy conversion, and beyond.