Small-sized tungsten nitride anchoring into a 3D CNT-rGO framework as a superior bifunctional catalyst for the methanol oxidation and oxygen reduction reactions

The application of direct methanol fuel cells (DMFC) is hampered by high cost, low activity, and poor CO tolerance by the Pt catalyst. Herein, we designed a fancy 3D hybrid by anchoring tungsten nitride (WN) nanoparticles (NPs), of about 3 nm in size, into a 3D carbon nanotube-reduced graphene oxide framework (CNT-rGO) using an assembly route. After depositing Pt, the contacted and strongly coupled Pt–WN NPs were formed, resulting in electron transfer from Pt to WN. The 3D Pt–WN/CNT-rGO hybrid can be used as a bifunctional electrocatalyst for both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). In MOR, the catalysts showed excellent CO tolerance and a high mass activity of 702.4 mA·mg_Pt ^–1, 2.44 and 3.81 times higher than those of Pt/CNT-rGO and Pt/C(JM) catalysts, respectively. The catalyst also exhibited a more positive onset potential (1.03 V), higher mass activity (151.3 mA·mg_Pt ^–1), and better cyclic stability and tolerance in MOR than ORR. The catalyst mainly exhibited a 4e-transfer mechanism with a low peroxide yield. The high activity was closely related to hybrid structure. That is, the 3D framework provided a favorable path for mass-transfer, the CNT-rGO support was favorable for charge transfer, and strongly coupled Pt–WN can enhance the catalytic activity and CO-tolerance of Pt. Pt–WN/CNT-rGO represents a new 3D catalytic platform that is promising as an electrocatalyst for DMFC because it can catalyze both ORR and MOR in an acidic medium with good stability and highly efficient Pt utilization.

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Mass production of highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation using an electron-beam irradiation reduction method

An electron-beam irradiation reduction method (EBIRM) is a technique to reduce metal ions in an aqueous solution via irradiation with a high-energy electron beam. In this study, an EBIRM is improved to develop a technique for the mass production of highly loaded and highly dispersed PtRu/C catalysts for use as direct methanol fuel cell anodes. An increase in the Pt and Ru input concentrations increased the loading weight from 9 to 37 wt%; however, the dispersibility of the PtRu nanoparticles on the carbon particles decreased. To improve the low dispersibility, sodium phosphinate was added to the precursor solution and the input amount of carbon particles was decreased. These changes resulted in not only highly loaded but also highly dispersed PtRu/C catalysts. The catalytic activity of the highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation was at least 1.6 times higher than that of the lowly loaded and lowly dispersed PtRu/C catalysts in all voltage range. More than 6000 mg of highly loaded and highly dispersed PtRu/C catalysts were relatively easily obtained, and the average particle size of the PtRu nanoparticles was 1.8 nm. These results demonstrated that the improved EBIRM is effective for the mass production of carbon-supported, highly loaded, and highly dispersed metal nanoparticles.     

Nanocomposite for methanol oxidation: synthesis and characterization of cubic Pt nanoparticles on graphene sheets

Abstract

We present our recent results on Pt nanoparticles on graphene sheets (Pt-NPs/G), a nanocomposite prepared with microwave assistance in ionic liquid 2-hydroxyethanaminiumformate. Preparation of Pt-NPs/G was achieved without the addition of extra reductant such as hydrazine or ethylene glycol. The Pt nanoparticles on graphene have a cubic-like shape (about 60 wt% Pt loading, Pt-NPs/G) and the particle size is 6 ± 3 nm from transmission electron microscopy results. Electrochemical cyclic voltammetry studies in 0.5 M aqueous H₂SO₄ were performed using Pt-NPs/G and separately, for comparison, using a commercially available electrocatalyst (60 wt% Pt loading, Pt/C). The electrochemical surface ratio of Pt-NPs/G to Pt/C is 0.745. The results of a methanol oxidation reaction (MOR) in 0.5 M aqueous H₂SO₄ + 1.0 M methanol for the two samples are presented. The MOR results show that the ratios of the current density of oxidation (I_f) to the current density of reduction (I_b) are 3.49 (Pt-NPs/G) and 1.37 (Pt/C), respectively, with a preference by 2.55 times favoring Pt-NPs/G. That is, the tolerance CO poisoning of Pt-NPs/G is better than that of commercial Pt/C.     

Organic-acid-assisted synthesis of a 3D lasagna-like Fe-N-doped CNTs-G framework: An efficient and stable electrocatalyst for oxygen reduction reactions

The scalable preparation of multi-functional three-dimensional (3D) carbon nanotubes and graphene (CNTs-G) hybrids via a well-controlled route is urgently required and challenging.Herein,an easily operated,oxalic acid-assisted method was developed for the in situ fabrication of a 3D lasagna-like Fe-N-doped CNTs-G framework (LMFC) from a precursor designed at the molecular level.The well-organized architecture of LMFC was constructed by multi-dimensionally interconnected graphene and CNTs which derived from porous graphene sheets,to form a fundamentally robust and hierarchical porous structure,as well as favorable conductive networks.The impressive oxygen reduction reaction (ORR) performances in both alkaline and acidic conditions helped confirm the significance of this technically favorable morphological structure.This product was also the subject of research for the exploration of decisive effects on the performance of ORR catalysts with reasonable control variables.The present work further advances the construction of novel 3D carbon architectures via practical and economic routes.