Carbon-coated nanoparticle superlattices for energy applications

Multi-Scale Engineered 2D Carbon Polyhedron Array with Enhanced Electrocatalytic Performance

Electrocatalyst engineering from the atomic to macroscopic level of electrocatalysts is one of the most powerful routes to boost the performance of electrochemical devices. However, multi-scale structure engineering mainly focuses on the range of atomic-to-particle scale such as hierarchical porosity engineering, while catalyst engineering at the macroscopic level, such as the arrangement configuration of nanoparticles, is often overlooked. Here, a 2D carbon polyhedron array with a multi-scale engineered structure via facile chemical etching, ice-templating induced self-assembly, and high-temperature pyrolysis processes is reported. Controlled phytic acid etching of the carbon precursor introduces homogeneous atomic phosphorous and nitrogen doping, as well as a well-defined mesoporous structure. Subsequent ice-templated self-assembly triggers the formation of a 2D particle array superstructure. The atomic-level doping gives rise to high intrinsic activity, while the well-engineered porous structure and particle arrangement addresses the mass transport limitations at the microscopic particle level and macroscopic electrode level. As a result, the as-prepared electrocatalyst delivers outstanding performance toward oxygen reduction reaction in both acidic and alkaline media, which is better than recently reported state-of-the-art metal-free electrocatalysts. Molecular dynamics simulation together with extensive characterizations indicate that the performance enhancement originates from multi-scale structural synergy.

Monolayer supertubes of Carbon-Armored platinum nanocrystals enabling robust oxygen reduction electrocatalysis

Self-assembled superstructures composed of nanocrystals (NCs) have shown immense potential for enhancing the performance in electrocatalytic applications. However, there has been limited research on the self-assembly of platinum (Pt) into low-dimensional superstructures as efficient electrocatalysts for oxygen reduction reaction (ORR). In this study, we designed a unique tubular superstructure composed of monolayer or sub-monolayer carbon-armored platinum nanocrystals (Pt NCs) using a template-assisted epitaxial assembly approach. The organic ligands on the surface of Pt NCs were in situ carbonized, resulting in few-layer graphitic carbon shells that encapsulate Pt NCs. Due to their monolayer assembly and tubular geometry, the Pt utilization of the supertubes was 1.5 times higher than that of conventional carbon-supported Pt NCs. As a result, such Pt supertubes exhibit remarkable electrocatalytic performance for the ORR in acidic media, with a high half-wave potential of 0.918 V and a high mass activity of 181 A g^-1_Pt at 0.9 V, which are comparable to commercial carbon-supported Pt (Pt/C) catalysts. Furthermore, the Pt supertubes demonstrate robust catalytic stability, as confirmed by long-term accelerated durability tests and identical-location transmission electron microscopy. This study presents a new approach to designing Pt superstructures for highly efficient and stable electrocatalysis.

Tension-compression behavior in gold nanoparticle arrays: a molecular dynamics study

The mechanical properties of Au nanoparticle arrays are studied by tensile and compressive deformation, using large-scale molecular dynamics simulations which include up to 16 million atoms. Our results show that mechanical response is dominated by nanoparticle size. For compression, strength versus particle size shows similar trends in strength than full-density nanocrystals. For diameters (d) below 10 nm there is an inverse Hall-Petch (HP) regime. Beyond a maximum at 10 nm, strength decreases following a HP d ^-1/2 dependence. In both regimes, interparticle sliding and dislocation activity play a role. The array with 10 nm nanoparticles showed the same mechanical properties than a polycrystalline bulk with the same grain size. This enhanced strength, for a material nearly 20% lighter, is attributed to the absence of grain boundary junctions, and to the array geometry, which leads to constant flow stress by means of densification, nanoparticle rotation, and dislocation activity. For tension, there is something akin to brittle fracture for large grain sizes, with NPs debonding perpendicular to the traction direction. The Johnson-Kendall-Roberts contact theory was successfully applied to describe the superlattice porosity, predicting also the array strength within 10% of molecular dynamics values. Although this study is focused on Au nanoparticles, our findings could be helpful in future studies of similar arrays with NPs of different kinds of materials.

Pd@C core-shell nanoparticles on carbon nanotubes as highly stable and selective catalysts for hydrogenation of acetylene to ethylene

Developing highly selective and stable catalysts for acetylene hydrogenation is an imperative task in the chemical industry. Herein, core-shell Pd@carbon nanoparticles supported on carbon nanotubes (Pd@C/CNTs) were synthesized. During the hydrogenation of acetylene, the selectivity of Pd@C/CNTs to ethylene was distinctly improved. Moreover, Pd@C/CNTs showed excellent stability during the hydrogenation reaction.