Facet‐Dependent and Light‐Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold–Palladium Core–Shell Nanocatalysts

Abstract

Au-Pd core-shell nanocrystals with tetrahexahedral (THH), cubic,a nd octahedral shapes and comparable sizes were synthesized. Similar-sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen-evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts.I np articular,A u-Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3-fold rate enhancement benefiting from lattice strain, modified surface electronic state,and abroader range of light absorption. Finite-difference time-domain (FDTD) simulations show astronger electric field enhancement on Au-Pd core-shell THH than those on other Pd-containing nanocrystals.Light-assisted nitro reduction by ammonia borane on Au-Pd THH was also demonstrated. Au-Pd tetrahexahedra supported on activated carbon can act as asuperior recyclable plasmonic photocatalyst for hydrogen evolution.Plasmonic metal nanocrystals such as Au,A g, and Pd have been synthesized in aqueous solutions with well-defined shapes,s uch as cubic and octahedral structures. [1][2][3][4][5][6][7] Their clean surfaces have enabled the evaluation of facet effects on organocatalysis with product selectivity. [8][9][10] Similarly,b imetallic Au-Pd and Au-Ag core-shell nanocrystals with tunable shapes and sizes can also be prepared in aqueous solutions and be used for facet-dependent catalytic examinations. [11][12][13][14][15][16] It has been shown that Pd nanocrystals are not only useful in various organic reactions but they can also be applied for hydrogen gas production through dehydrogenation of ammonia borane (NH 3 BH 3 ). [17][18][19][20][21][22] Ammonia borane (AB) is apromising hydrogen-storage material because of its high hydrogen storage capacity (19.6 wt %) among all practical hydrogenstorage materials. [23,24] It is highly soluble in water and inert toward hydrolysis,b ut produces hydrogen gas only in the presence of as uitable catalyst. [17][18][19][20][25][26][27][28] Development of simple and highly efficient catalysts for the dehydrogenation of AB is desirable.Previous notable examples used sub-10 nm spherical Pd and CoPd alloy nanoparticles to catalyze this reaction. [17][18][19][20] Facet effects on catalytic efficiencyh ave not been examined for this reaction. It should be interesting to use cubic and octahedral Pd nanocrystals for the dehydrogenation of AB.In addition to employing pure Pd nanocrystals as the catalyst, use of polyhedral Au-Pd core-shell heterostructures for hydrogen generation can be advantageous because Pd surface property can be modified slightly by the Au cores,and the particles can absorb aw ider range of visible light. Such nanostructures can be used in plasmonic photocatalysis to improve catalytic efficiency. Fore xample,b imetallic AuPd nanowheels can serve as ah ighly efficient catalyst in the oxidation of benzyl alcohol and Suzuki coupling reaction under light irradiation.[29] Pd-tipped Au nanorods have exhib...

Bimetallic AuRh nanodendrites consisting of Au icosahedron cores and atomically ultrathin Rh nanoplate shells: synthesis and light-enhanced catalytic activity

“…When Au based core-shell nanostructures are exposed to light, the electron transfer of the Au core to the metal shell generally results in the charge enrichment on the metal shell. [15][16][17] Previous investigations have demonstrated that the electronic properties of the metal surface have a crucial role for the HGR-N 2 H 4 because N-N and N-H bond cleavage is closely related to the electronic structure of metal atoms. 27,56 For the Au@Rh core-shell nanodendrites under light irradiation conditions, the charge-enriched Rh shells effectively weaken the N-H bond and reduce the activation barrier energy, 57,58 resulting in light-enhanced catalytic activity.…”

“…12,13 Among various bimetallic nanostructures, Au-based core-shell-type noble metal nanostructures have been widely employed in various important heterogeneous catalytic reactions, especially in lightenhanced catalytic reactions, originating from the high mass activity of noble metal shells and the distinctive localized surface plasmon resonance (LSPR) of Au nanocrystal cores. [14][15][16][17] In most bimetallic core-shell nanodendrites, the metal shells consist of spherical nanocrystals. 5,18,19 Recently, the atomically thick noble metal nanoplates, an emerging star nanomaterial for the catalysis, have attracted more attention compared with the traditional zerodimensional noble metal nanocrystals, owing to the extremely high meal atom utilization and superior catalytic activity.…”

Visible-Light Acceleration of H2 Evolution from Aqueous Solutions of Inorganic Hydrides Catalyzed by Gold-Transition-Metal Nanoalloys

“…Visible-light acceleration of a number of various catalytic reactions of synthetic and environmental interest has been reported for plasmonic gold as part of heterobimetallic catalysts. 12 In particular, interest has recently focused on plasmon induced light acceleration of hydrolysis of ammonia-borane (AB), NH3BH3, by coinage metal NPs using heterobimetallic nanocatalysts either coupled to [13][14][15][16][17][18] or without a semi-conductor. [19][20][21][22][23] Inorganic hydrides such as AB and sodium borohydride, NaBH4, are promising hydrogen storage compounds, [24][25][26] because they are stable solids with high colloidal solubility in water, contain a high proportion of hydrogen and are easily transported contrary to explosive hydrogen gas.…”

Robust Synthesis of Gold‐Based Multishell Structures as Plasmonic Catalysts for Selective Hydrogenation of 4‐Nitrostyrene

“…The NH 3 ·BH 3 -initiated hydrogenation of am ixture of nitrobenzene and styrene was further tested using two catalysts.T he results (Supporting Information, Table S1) show that PTSAu/ ZrO 2 are active towards reduction of Ar-NO 2 and Ar-C = C, while the S-PTSAu/ZrO 2 activate only Ar-NO 2, not Ar-C = C. Thetransfer hydrogenation processes have been proposed in AB-initiated hydrogenation reactions. [28][29][30] In these processes, the polarized hydrogen atom in NH 3 ·BH 3 would transfer to unsaturated groups. [28][29][30][31] Them odification of sulfhydryl species on Au surface might influence polarized hydrogen transfer towards À C = C, finally resulting in their high selectivity.T he unmodified Au/ZrO 2 was also synthesized (Supporting Information, Figure S11c) by simple reduction of the HAuCl 4 and ZrO 2 nanoparticle mixture solution with NaBH 4 .…”

“…[28][29][30] In these processes, the polarized hydrogen atom in NH 3 ·BH 3 would transfer to unsaturated groups. [28][29][30][31] Them odification of sulfhydryl species on Au surface might influence polarized hydrogen transfer towards À C = C, finally resulting in their high selectivity.T he unmodified Au/ZrO 2 was also synthesized (Supporting Information, Figure S11c) by simple reduction of the HAuCl 4 and ZrO 2 nanoparticle mixture solution with NaBH 4 . To confirm the influence of sulfhydryl species modification, the Au/ZrO 2 was further treated with l-cystine to obtain modified sample (S-Au/ZrO 2 ).…”