Bao Yu Xia

Porous molybdenum carbide nano-octahedrons synthesized via confined carburization in metal-organic frameworks for efficient hydrogen production

Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

Designed Formation of Co3O4/NiCo2O4 Double-Shelled Nanocages with Enhanced Pseudocapacitive and Electrocatalytic Properties

Hollow structures with high complexity in shell architecture and composition have attracted tremendous interest because of their great importance for both fundamental studies and practical applications. Herein we report the designed synthesis of novel box-in-box nanocages (NCs) with different shell compositions, namely, Co3O4/NiCo2O4 double-shelled nanocages (DSNCs). Uniform zeolitic imidazolate framework-67/Ni-Co layered double hydroxides yolk-shelled structures are first synthesized and then transformed into Co3O4/NiCo2O4 DSNCs by thermal annealing in air. Importantly, this strategy can be easily extended to prepare other complex DSNCs. When evaluated as electrodes for pseudocapacitors, the Co3O4/NiCo2O4 DSNCs show a high specific capacitance of 972 F g(-1) at a current density of 5 A g(-1) and excellent stability with 92.5% capacitance retention after 12 000 cycles, superior to that of Co3O4 NCs with simple configuration and Co3O4/Co3O4 DSNCs. Besides, the Co3O4/NiCo2O4 DSNCs also exhibit much better electrocatalytic activity for the oxygen evolution reaction than Co3O4 NCs. The greatly improved electrochemical performance of Co3O4/NiCo2O4 DSNCs demonstrates the importance of rational design and synthesis of hollow structures with higher complexity.

One-Pot Synthesis of Cubic PtCu3 Nanocages with Enhanced Electrocatalytic Activity for the Methanol Oxidation Reaction

Noble metals such as platinum (Pt) are widely used as catalysts in fuel cells and other heterogeneous catalytic processes. However, there is an urgent need to develop substitutes for pure Pt catalysts to reduce the overall use of precious Pt and at the same time to enhance poisoning resistance. A promising strategy is to design Pt based bi- or trimetallic nanostructures because their unique structures and compositions would enhance their catalytic performance. In this study, we report the synthesis, characterization, and electrochemical evaluation of cubic intermetallic PtCu(3) nanocages. The influential effects of several important experimental parameters on the final products have been explored through systematic studies on the growth of PtCu(3) nanocages. Relative to the current commercial Pt electrocatalyst, these PtCu(3) nanocages possess a more accessible surface area and a unique hollow structure, which contribute to improved electrocatalytic activity in the methanol oxidation reaction.

Ultrathin and Ultralong Single-Crystal Platinum Nanowire Assemblies with Highly Stable Electrocatalytic Activity

Ultrathin one-dimensional (1D) nanostructures such as nanowires and nanorods have drawn considerable attention due to their promising applications in various fields. Despite the numerous reports on 1D nanostructures of noble metals, one-pot solution synthesis of Pt 1D nanostructures still remains a great challenge, probably because of the intrinsic isotropic crystal growth behavior of Pt. Herein, we demonstrate the facile solvothermal synthesis of nanowire assemblies composed of ultrathin (ca. 3 nm) and ultralong (up to 10 μm) Pt nanowires without involving any template. The oriented attachment mechanism is found to be partially responsible for the formation of such ultrathin Pt nanowires. The amine molecules generated during the reaction might assist the formation of nanowire assemblies. Importantly, the present system can be extended to synthesize Pt-based alloy nanowire assemblies such as Pt-Au and Pt-Pd. These Pt nanowires can be easily cast into a free-standing membrane, which exhibits excellent electrocatalytic activity and very high stability for formic acid and methanol oxidation and the oxygen reduction reaction.

Hierarchical β‐Mo2C Nanotubes Organized by Ultrathin Nanosheets as a Highly Efficient Electrocatalyst for Hydrogen Production

Production of hydrogen by electrochemical water splitting has been hindered by the high cost of precious metal catalysts, such as Pt, for the hydrogen evolution reaction (HER). In this work, novel hierarchical β-Mo2 C nanotubes constructed from porous nanosheets have been fabricated and investigated as a high-performance and low-cost electrocatalyst for HER. An unusual template-engaged strategy has been utilized to controllably synthesize Mo-polydopamine nanotubes, which are further converted into hierarchical β-Mo2 C nanotubes by direct carburization at high temperature. Benefitting from several structural advantages including ultrafine primary nanocrystallites, large exposed surface, fast charge transfer, and unique tubular structure, the as-prepared hierarchical β-Mo2 C nanotubes exhibit excellent electrocatalytic performance for HER with small overpotential in both acidic and basic conditions, as well as remarkable stability.

Ultrathin MoS2 Nanoplates with Rich Active Sites as Highly Efficient Catalyst for Hydrogen Evolution

Well-defined ultrathin MoS2 nanoplates are developed by a facile solvent-dependent control route from single-source precursor for the first time. The obtained ultrathin nanoplate with a thickness of ~ 5 nm features high density of basal edges and abundant unsaturated active S atoms. The multistage growth process is investigated and the formation mechanism is proposed. Ultrathin MoS2 nanoplates exhibit an excellent activity for hydrogen evolution reaction (HER) with a small onset potential of 0.09 V, a low Tafel slope of 53 mV dec(-1), and remarkable stability. This work successfully demonstrates that the introduction of unsaturated active S atoms into ultrathin MoS2 nanoplates for enhanced electrocatalytic properties is feasible through a facial one-step solvent control method, and that this may open up a potential way for designing more efficient MoS2-based catalysts for HER.

Recent progress on graphene-based hybrid electrocatalysts

Graphene-based hybrid nanostructures have attracted increasing interest worldwide. Benefiting from their remarkable electrochemical catalytic properties derived from chemical compositions and synergetic effects of multi-functionalities, these graphene-based hybrid nanomaterials will play a significant role in cutting-edge innovation for novel electrocatalysts. In this review, we summarize recent progress in the design and synthesis of graphene-based hybrid nanomaterials with controlled shape, size, composition and structure, and their application as efficient electrocatalysts for energy related systems. We conclude this article with some future trends and prospects which are highlighted for further investigations on graphene-based nanomaterials as advanced electrocatalysts.

Strongly Coupled NiCo2O4‐rGO Hybrid Nanosheets as a Methanol‐Tolerant Electrocatalyst for the Oxygen Reduction Reaction

Strongly coupled NiCo2 O4 -rGO hybrid nanosheets are syntheiszed through a cost-effective two-step strategy involving a facile polyol process and subsequent thermal annealing treatment in air. The hybrid nanosheets exhibit impressive electrocatalytic performance for the oxygen reduction reaction (ORR) with a current density and onset potential comparable to those of commercial Pt/C catalyts, while having perfect tolerance to methanol..

One‐Pot Synthesis of Pt–Co Alloy Nanowire Assemblies with Tunable Composition and Enhanced Electrocatalytic Properties

Three-dimensional (3D) Pt-based alloy nanostructures composed of one-dimensional (1D) nanowires/nanorods have recently attracted significant interest as electrocatalysts. In this work, we report an effective solvothermal method for the direct preparation of 3D Pt-Co nanowire assemblies (NWAs) with tunable composition. The composition- and structure-dependent electrocatalytic performance is thoroughly investigated. Because of the bimetallic synergetic effect and unique structural advantage, the as-prepared 3D Pt3Co NWA outperforms commercial Pt/carbon and Pt black catalysts and even 3D Pt NWA. The electrochemical results demonstrate that the 3D Pt3Co NWA is indeed a promising electrocatalyst with enhanced catalytic activity and improved durability for practical electrocatalytic applications.

Self‐Supported Interconnected Pt Nanoassemblies as Highly Stable Electrocatalysts for Low‐Temperature Fuel Cells

In it for the long haul: Clusters of Pt nanowires (3D Pt nanoassemblies, Pt NA) serve as an electrocatalyst for low-temperature fuel cells. These Pt nanoassemblies exhibit remarkably high stability following thousands of voltage cycles and good catalytic activity, when compared with a commercial Pt catalyst and 20 % wt Pt catalyst supported on carbon black (20 % Pt/CB).