Synthesis of amorphous trimetallic PdCuNiP nanoparticles for enhanced OER.

Metal phosphides with multi-element components and amorphous structure represent a novel kind of electrocatalysts for promising activity and durability towards the oxygen evolution reaction (OER). In this work, a two-step strategy, including alloying and phosphating processes, is reported to synthesize trimetallic amorphous PdCuNiP phosphide nanoparticles for efficient OER under alkaline conditions. The synergistic effect between Pd, Cu, Ni, and P elements, as well as the amorphous structure of the obtained PdCuNiP phosphide nanoparticles, would boost the intrinsic catalytic activity of Pd nanoparticles towards a wide range of reactions. These obtained trimetallic amorphous PdCuNiP phosphide nanoparticles exhibit long-term stability, nearly a 20-fold increase in mass activity toward OER compared with the initial Pd nanoparticles, and 223 mV lower in overpotential at 10 mA cm-2. This work not only provides a reliable synthetic strategy for multi-metallic phosphide nanoparticles, but also expands the potential applications of this promising class of multi-metallic amorphous phosphides.

Tailoring Amorphous PdCu Nanostructures for Efficient C-C Cleavage in Ethanol Electrooxidation.

The large-scale application of direct ethanol fuel cells has long been obstructed by the sluggish ethanol oxidation reaction at the anode. Current wisdom for designing and fabricating EOR electrocatalysts has been focused on crystalline materials, which result in only limited improvement in catalytic efficiency. Here, we report the amorphous PdCu (a-PdCu) nanomaterials as superior EOR electrocatalysts. The amorphization of PdCu catalysts can significantly facilitate the C-C bond cleavage, which thereby affords a C1 path faradic efficiency as high as 69.6%. Further tailoring the size and shape of a-PdCu nanocatalysts through the delicate kinetic control can result in a maximized mass activity up to 15.25 A/mgPd, outperforming most reported catalysts. Notably, accelerated durability tests indicate that both the isotropic structure and one-dimensional shape can dramatically enhance the catalytic durability of the catalysts. This work provides valuable guidance for the rational design and fabrication of amorphous noble metal-based electrocatalysts for fuel cells.

Mastering the surface strain of platinum catalysts for efficient electrocatalysis.

Platinum (Pt) has found wide use as an electrocatalyst for sustainable energy conversion systems1-3. The activity of Pt is controlled by its electronic structure (typically, the d-band centre), which depends sensitively on lattice strain4,5. This dependence can be exploited for catalyst design4,6-8, and the use of core-shell structures and elastic substrates has resulted in strain-engineered Pt catalysts with drastically improved electrocatalytic performances7,9-13. However, it is challenging to map in detail the strain-activity correlations in Pt-catalysed conversions, which can involve a number of distinct processes, and to identify the optimal strain modification for specific reactions. Here we show that when ultrathin Pt shells are deposited on palladium-based nanocubes, expansion and shrinkage of the nanocubes through phosphorization and dephosphorization induces strain in the Pt(100) lattice that can be adjusted from -5.1 per cent to 5.9 per cent. We use this strain control to tune the electrocatalytic activity of the Pt shells over a wide range, finding that the strain-activity correlation for the methanol oxidation reaction and hydrogen evolution reaction follows an M-shaped curve and a volcano-shaped curve, respectively. We anticipate that our approach can be used to screen out lattice strain that will optimize the performance of Pt catalysts-and potentially other metal catalysts-for a wide range of reactions.

General Synthesis of Amorphous PdM (M = Cu, Fe, Co, Ni) Alloy Nanowires for Boosting HCOOH Dehydrogenation.

Noble metal-based nanomaterials with amorphous structures are promising candidates for developing efficient electrocatalysts. However, their synthesis remains a significant challenge, especially under mild conditions. In this paper, we report a general strategy for preparing amorphous PdM nanowires (a-PdM NWs, M = Fe, Co, Ni, and Cu) at low temperatures by exploiting glassy non-noble metal (M) nuclei generated by special ligand adsorption as the amorphization dictator. When evaluated as electrocatalysts toward formic acid oxidation, a-PdCu NWs can deliver the mass and specific activities as high as 2.93 A/mgPd and 5.33 mA/cm2, respectively; these are the highest values for PdCu-based catalysts reported thus far, far surpassing the crystalline-dominant counterparts and commercial Pd/C. Theoretical calculations suggest that the outstanding catalytic performance of a-PdCu NWs arises from the amorphization-induced high surface reactivity, which can efficiently activate the chemically stable C-H bond and thereby significantly facilitate the dissociation of HCOOH.

Deposition of Atomically Thin Pt Shells on Amorphous Palladium Phosphide Cores for Enhancing the Electrocatalytic Durability.

As an excellent electrocatalyst, platinum (Pt) is often deposited as a thin layer on a nanoscale substrate to achieve high utilization efficiency. However, the practical application of the as-designed catalysts has been substantially restricted by the poor durability arising from the leaching of cores. Herein, by employing amorphous palladium phosphide (a-Pd-P) as substrates, we develop a class of leaching-free, ultrastable core-shell Pt catalysts with well-controlled shell thicknesses and surface structures for fuel cell electrocatalysis. When a submonolayer of Pt is deposited on the 6 nm nanocubes, the resulting Pd@a-Pd-P@PtSML core-shell catalyst can deliver a mass activity as high as 4.08 A/mgPt and 1.37 A/mgPd+Pt toward the oxygen reduction reaction at 0.9 V vs the reversible hydrogen electrode and undergoes 50 000 potential cycles with only ∼9% activity loss and negligible structural deformation. As elucidated by the DFT calculations, the superior durability of the catalysts originates from the high corrosion resistance of the disordered a-Pd-P substrates and the strong interfacial Pt-P interactions between the Pt shell and amorphous Pd-P layer.

Engineering Surface Structure of Pt Nanoshells on Pd Nanocubes to Preferentially Expose Active Surfaces for ORR by Manipulating the Growth Kinetics.

Synthesis of Pt nanoshells on substrates can increase the utilization efficiency of Pt atoms and reduce the amount of Pt used in the applications. However, it is still an enormous challenge in tailoring the required crystal facets of Pt nanoshells on a given substrate. In this work, we demonstrate a facile and convenient approach capable for generating Pt octahedral islands with tunable sizes and densities on Pd nanocubes by manipulating the deposition rate. The key to this synthesis is the fine control over the deposition rate of Pt on Pd seeds. Because of the different reactivities at the surface sites, the deposition of Pt can be controlled at a certain site by carefully tuning the deposition rate. With a low concentration of reductant (8.33 mg/mL of glucose), surface diffusion dominates the process, and thus the Pt cubic shells form on Pd cubic seeds. In contrast, when a higher amount of the reductant (16.67 mg/mL of glucose) is added, the deposition starts to dominate the growth of Pt shells. In this case, the deposition would be controlled at the corners, forming eight large Pt octahedra on a cubic Pd seed. Further increasing the deposition rate can induce much higher deposition rates, in which case, the deposition of Pt would likely take place not only at the corners, but also the edge and surface sites of the seeds. Not surprisingly, this growth habit can result in the formation of high-density octahedral islands on Pd cubic seeds. With the same amount of precursor supply, the higher the densities of Pt islands, the smaller the size of the octahedral islands on Pd nanocubes. Unlike other synthetic methods, the size of the octahedral islands on Pd seeds can be even controlled to be smaller than 3 nm by controlling the amount of the Pt precursor. Considering the excellent performance of {111} facets of Pt catalysts toward ORR, the Pt nanocages with small octahedral islands on the surfaces can exhibit a high activity with a mass activity 0.68 A/mg, as high as 5.2 times of that of commercial Pt/C.

Synthesis of Pd Nanoframes by Excavating Solid Nanocrystals for Enhanced Catalytic Properties.

Synthesis of metal nanoframes has been of great interest for their open structures and high fractions of active surface sites, which gives rise to outstanding performance in catalysis. In this work, Pd nanoframes with well-defined structures have been successfully prepared by directly excavating solid nanocrystals. The success of this synthesis mainly relies on the fine control over the oxidative etching and regrowth rates. Due to the different regrowth rates at three typical types of surface sites (e.g., corners, edges, and faces), the removal of Pd atoms can be controlled at a certain site by carefully tuning the rates of the oxidative etching and regrowth. Without the presence of the reducing agent, etching dominates the process, resulting in the shape transformation of nanocrystals with well-defined shapes (e.g., octahedra) to cuboctahedra. In contrast, when a certain amount of the reducing agent (e.g., HCHO) is added, the regrowth rate at the corner and edge sites can be controlled to be equivalent to the etching rate, while the regrowth rate at the face sites is still smaller than the etching rate. In this case, the etching can only take place at the faces; thus, Pd nanoframes could be obtained. On the basis of this approach, solid Pd nanocrystals with different shapes, including cubes, cuboctahedra, octahedra, and concave cubes, have been successfully excavated to the corresponding nanoframes. These nanoframes can unambiguously exhibit much enhanced catalytic activity and improved durability toward formic acid oxidation reaction due to their three-dimensional (3D) open frameworks compared with solid Pd octahedra catalysts.