Electrodeposited AgCu Foam Catalysts for Enhanced Reduction of CO2 to CO.

Selective electrochemical reduction of CO2 is an emerging field which needs more active and stable catalysts for its practicability. In this work, we have studied the influence of Ag metal incorporation into Cu dendritic structures on the product distribution and selectivity of CO2 electroreduction. Bimetallic AgCu foams prepared by hydrogen bubble templated electrodeposition shift the potentials of CO production to more positive values compared to bulk silver. The presence of Ag during the electrodeposition significantly changed the size and the shape of the dendrites in the pore walls of AgCu foams compared to Cu foam. The CO adsorption characteristics are studied by operando Raman spectroscopy. In the presence of Ag, the maximum CO adsorption is observed at a more positive potential. As a result, an improved selectivity for CO is obtained for AgCu foam catalysts at lower overpotentials compared to Cu foam catalyst, evidencing a synergistic effect between the bimetallic components. We were successful in increasing the CO mass activity with respect to the total Ag amount. AgCu foams are found to retain the CO selectivity during long-term operation, and with their easily scalable electrodeposition synthesis they possess high potential for industrial application.

Roles of Mo Surface Dopants in Enhancing the ORR Performance of Octahedral PtNi Nanoparticles.

Doping with a transition metal was recently shown to greatly boost the activity and durability of PtNi/C octahedral nanoparticles (NPs) for the oxygen reduction reaction (ORR), but its specific roles remain unclear. By combining electrochemistry, ex situ and in situ spectroscopic techniques, density functional theory calculations, and a newly developed kinetic Monte Carlo model, we showed that Mo atoms are preferentially located on the vertex and edge sites of Mo-PtNi/C in the form of oxides, which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides stabilize adjacent Pt sites, hereby stabilizing the octahedral shape enriched with (111) facets, and lead to increased concentration of Ni in subsurface layers where they are protected against acid dissolution. Consequently, the favorable Pt3Ni(111) structure for the ORR is stabilized on the surface of PtNi/C NPs in acid against voltage cycling. Significantly, the unusual potential-dependent oxygen coverage trend on Mo-doped PtNi/C NPs as revealed by the surface-sensitive Δµ analysis suggests that the Mo dopants may also improve the ORR kinetics by modifying the coordination environments of Pt atoms on the surface. Our studies point out a possible way to stabilize the favorable shape and composition established on conceptual catalytic models in practical nanoscale catalysts.

Experimental Proof of the Bifunctional Mechanism for the Hydrogen Oxidation in Alkaline Media.

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data, which provide convincing evidence for the presence of hydroxy groups on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.