We investigated CO2 electroreduction on Cu overlayers on tetrahexahedral Pd nanocrystals with {310} high-index facets, which exhibited a high Faradaic efficiency towards alcohols. The selectivity to ethanol or methanol can be readily tuned by changing the Cu coverage.

Shape transformation of Pt nanocrystals from a {730}-bounded tetrahexahedron into a {310}-bounded truncated ditetragonal prism was achieved using the electrochemical square-wave potential method. The transformation process and mechanism were revealed. This study provides new insight into the nanocrystal growth habit.

Controlling the surface structure of Pt nanocrystals (NCs), especially creating high-index facets with abundant active step sites, is an effective approach to enhance catalytic performances. However, the available high-index faceted Pt NCs have large particle sizes, which severely impedes their practical applications. In this study, we reported a new electrochemically seed-mediated method, by which sub-10 nm tetrahexahedral Pt NCs (THH Pt NCs) enclosed with {210} high-index facets supported on graphene were synthesized. Pt nanoparticles of ∼3 nm in size as high-density crystal seeds play a key role in the small-sized control. The obtained THH Pt NCs exhibited a higher mass activity than commercial Pt/C catalyst for ethanol electrooxidation. We further demonstrated that this method is also valid for reshaping commercial Pt/C, to create high-index facets on surfaces and thus to improve both mass activity and stability.

Systematic manipulation of nanocrystal shapes is prerequisite for revealing their shape-dependent physical and chemical properties. Here we successfully prepared a complex shape of Pt micro/nanocrystals: convex hexoctahedron (HOH) enclosed with 48 {15 5 3} high-index facets by electrochemical square-wave-potential (SWP) method. This shape is the last crystal single form that had not been achieved previously for face-centered-cubic (fcc) metals. We further realized the shape evolution of Pt nanocrystals with high-index facets from tetrahexahedron (THH) to the HOH, and finally to trapezohedron (TPH) by increasing either the upper (EU) or lower potential (EL). The shape evolution, accompanied by the decrease of low-coordinated kink atoms, can be correlated with the competitive interactions between preferentially oxidative dissolution of kink atoms at high EU and the redeposition of Pt atoms at the EL.

Alloy tetrahexahedral Pd–Pt nanocrystals (THH Pd–Pt NCs) mainly enclosed by {10 3 0} high-index facets were prepared by electrochemistry. The as-prepared THH Pd–Pt NCs exhibit a catalytic activity that is at least three times higher than the tetrahexahedral Pd catalysts, and six times higher than commercial Pd black catalysts for the electrooxidation of formic acid. The significant enhancement in catalytic activity has been attributed to the synergy effect of high-index facets and electronic structure of the alloy.

Tetrahexahedral Pt nanocrystals (THH Pt NCs) bound by well-defined high index crystal planes offer exceptional electrocatalytic activity, owing to a high density of low-coordination surface Pt sites. We report, herein, on methanol electrooxidation at THH Pt NC electrodes studied by a combination of electrochemical techniques and in situ FTIR spectroscopy. Pure THH Pt NC surfaces readily facilitate the dissociative chemisorption of methanol leading to poisoning by strongly adsorbed CO. Decoration of the stepped surfaces by Ru adatoms increases the tolerance to poisoning and thereby reduces the onset potential for methanol oxidation by over 100 mV. The Ru modified THH Pt NCs exhibit greatly superior catalytic currents and CO2 yields in the low potential range, when compared with a commercial PtRu alloy nanoparticle catalyst. These results are of fundamental importance in terms of model nanoparticle electrocatalytic systems of stepped surfaces and also have practical significance in the development of surface tailored, direct methanol fuel cell catalysts.Keywords: electrocatalysis; fuel cells; high index facets; methanol electrooxidation; Ru adatoms; tetrahexahedral platinum;

Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO2 production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.

•Octahedral PtCu nanocrystals have been synthesized by a developed facile strategy for the one-pot synthesis without using surfactants.•The area specific activity and mass activity of the synthesized octahedral PtCu/C reach 4.25 mA cm−2 and 1.20 mA µgPt−1 at 0.90 V (vs RHE), respectively, which are 21.3 and 8.6 times higher than those of commercial Pt/C catalyst.•A tiny amount of gold doping, without much compromising ORR activity, can suppress diffusion/dissolution of low-coordinated Pt atoms and greatly enhance the stability of octahedral PtCu alloy.In fuel cell technologies, the sluggish kinetics of oxygen reduction reaction (ORR) on the cathode is the main obstacle, and it is thus urgent to develop high-performance catalysts. In this work, we have synthesized 10 nm-sized octahedral PtCu alloy nanocrystals by a simple one-pot strategy using I- as shape-directing agent instead of using large surfactants. The area specific activity and mass activity of the synthesized octahedral PtCu/C reach 4.25 mA cm−2 and 1.20 mA μgPt−1 at 0.90 V (vs RHE), respectively, which are 21.3 and 8.6 times higher than those of commercial Pt/C catalysts. Unexpectedly, we found that the stability of PtCu/C can be enhanced dramatically by doping trace Au (Au/Pt =0.0005). The mass activity loss of PtCuAu0.0005/C was only 8%, much smaller than those of PtCu/C (32%), and Pt/C (52%) after 10,000 potential cycles. This study provides a strategic design of Pt-based efficient ORR catalysts for fuel cells.Compared with their high ORR activity, the stability of PtCu octahedral nanoparticles is not satisfied, which is hindered by the diffusion/ dissolution of low-coordinated Pt atoms at the defect sites. The trace Au atoms preferentially protects these Pt atoms and inhibits the diffusion/dissolution of these Pt atoms, which is helpful for the maintenance of the shape and thus might promise a high stability.

Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO2 production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.

We investigated CO2 electroreduction on Cu overlayers on tetrahexahedral Pd nanocrystals with {310} high-index facets, which exhibited a high Faradaic efficiency towards alcohols. The selectivity to ethanol or methanol can be readily tuned by changing the Cu coverage.

Alloy tetrahexahedral Pd–Pt nanocrystals (THH Pd–Pt NCs) mainly enclosed by {10 3 0} high-index facets were prepared by electrochemistry. The as-prepared THH Pd–Pt NCs exhibit a catalytic activity that is at least three times higher than the tetrahexahedral Pd catalysts, and six times higher than commercial Pd black catalysts for the electrooxidation of formic acid. The significant enhancement in catalytic activity has been attributed to the synergy effect of high-index facets and electronic structure of the alloy.

Shape transformation of Pt nanocrystals from a {730}-bounded tetrahexahedron into a {310}-bounded truncated ditetragonal prism was achieved using the electrochemical square-wave potential method. The transformation process and mechanism were revealed. This study provides new insight into the nanocrystal growth habit.