Au-MoS2 Hybrids as Hydrogen Evolution Electrocatalysts

Core-shell nanoparticles provide a unique morphology to exploit electronic interactions between dissimilar materials, conferring upon them new or improved functionalities. MoS2 is a layered transition-metal disulfide that has been studied extensively for the hydrogen evolution reaction (HER) but still suffers from low electrocatalytic activity due to its poor electronic conductivity. To understand the fundamental aspects of the MoS2-Au hybrids with regard to their electrocatalytic activity, a single to a few layers of MoS2 were deposited over Au nanoparticles via a versatile procedure that allows for complete encapsulation of Au nanoparticles of arbitrary geometries. High-resolution transmission electron microscopy of the Au@MoS2 nanoparticles provides direct evidence for the core-shell morphology and also reveals the presence of morphological defects and irregularities in the MoS2 shell that are known to be more active for HER than the pristine MoS2 basal plane. Electrochemical measurements show a significant improvement in the HER activity of Au@MoS2 nanoparticles relative to freestanding MoS2 or Au-decorated MoS2. The best electrochemical performance was demonstrated by the Au nanostars - the largest Au core employed here - encapsulated in a MoS2 shell. Density-functional theory calculations show that charge transfer occurs from the Au to the MoS2 layers, producing a more conductive catalyst layer and a better electrode for electrochemical HER. The strategies to further improve the catalytic properties of such hybrid nanoparticles are discussed

Efficacy of methylsulfonylmethane supplementation on osteoarthritis of the knee: a randomized controlled study

BACKGROUND: Patients with osteoarthritis (OA) take a variety of health supplements in an attempt to reduce pain and improve function. The aim of this study was to determine the efficacy of methylsulfonylmethane (MSM) in treating patients with knee OA. METHODS: This study was a prospective, randomized, double-blind, controlled clinical trial. Forty nine men and women 45-90 (mean 68 ± SD 7.3) years of age with knee OA according to the American College of Rheumatology clinical criteria for OA of the knee and with radiographic confirmed knee OA were enrolled in the study and randomly assigned into 2 groups: One received MSM in doses of 1.125 grams 3 times daily for 12 weeks and the other received a placebo in the same dosing frequency. The primary outcomes were the WOMAC Osteoarthritis Index for pain, stiffness and physical function, the Aggregated Locomotor Function (ALF) test that evaluates each patient's physical function, the SF-36 quality of life health survey and the visual-analogue-scale (VAS) for pain. The secondary outcomes were Knee Society Clinical Rating System for Knee Score (KSKS) and Function Score (KSFS). Patients were assessed at baseline, 6 weeks and 12 weeks. All continuous variables were tested by the Kolmogorov-Smirnov test for Normal distribution. Changes within the groups and differences between the groups were calculated by repeated measures of analysis (ANOVA) with one nested variable. RESULTS: There were significant differences between treatment groups over time in WOMAC physical function (14.6 mm [CI: 4.3, 25.0]; p = 0.04) and in WOMAC total score (15.0 mm [CI: 5.1, 24.9]; p = 0.03). Treatment groups did not differ significantly in WOMAC pain (12.4 mm [CI: 0.0, 24.8]); p = 0.08) or WOMAC stiffness (27.2 mm [CI: 8.2, 46.2]; p = 0.08). There was a non-significant difference in SF-36 total score between treatment groups (11.6 [CI: 1.0, 22.1]; p = 0.54). A significant difference was found between groups in VAS for pain (0.7 s [CI: -0.9, 2.4]; p = 0.05). Secondary outcomes showed non-significant differences between the two groups. CONCLUSIONS: Patients with OA of the knee taking MSM for 12 weeks showed an improvement in pain and physical function. These improvements, however, are small and it is yet to be determined if they are of clinical significance. TRIAL REGISTRATION: ClinicalTrials.gov: NCT0118821

The Competition between 4-Nitrophenol Reduction and BH₄⁻ Hydrolysis on Metal Nanoparticle Catalysts

Assessing competitive environmental catalytic reduction processes via NaBH4 is essential, as BH4− is both an energy carrier (as H2) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H2) and 4-nitrophenol reduction via BH4− on M0- and M/M′ (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH4− hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH4− hydrolysis. The investigated catalysts were Ag0, Au0, Pt0, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag0, Ag-Pt (9:1), and Au0 are significantly higher than the corresponding rate constants for BH4− hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt0 nanoparticles. This research emphasizes the conflicting nature of BH4− hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process

Catalysts for the hydrogen evolution reaction in alkaline medium: Configuring a cooperative mechanism at the Ag-Ag2S-MoS2 interface

Designing electrocatalysts for HER in alkaline conditions to overcome the sluggish kinetics associated with the additional water dissociation step is a recognized challenge in promoting the hydrogen economy. To this end, delicately tuning the atomic-scale structure and surface composition of nanoparticles is a common strategy and, specifically, making use of hybrid structures, can produce synergistic effects that lead to highly active catalysts. Here, we present a core-shell catalyst of Ag@MoS2 that shows promising results towards the hydrogen evolution reaction (HER) in both 0.5 M H2SO4 and 0.5 M KOH. In this hybrid structure, the MoS2 shell is strained and defective, and charge transfer occurs between the conductive core and the shell, contributing to the electrocatalytic activity. The shelling process results in a large fraction of Ag2S in the cores, and adjusting the relative fractions of Ag, Ag2S, and MoS2 leads to improved catalytic activity and fast charge-transfer kinetics. We suggest that the enhancement of alkaline HER is associated with a cooperative effect of the interfaces, where the Ag(I) sites in Ag2S drive the water dissociation step, and the formed hydrogen subsequently recombines on the defective MoS2 shell. This study demonstrates the benefits of hybrid structures as functional nanomaterials and provides a scheme to activate MoS2 for HER in alkaline conditions.This research was supported by the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel and the United States National Science Foundation (NSF) grant 2017642, and partly from the Israeli Atomic Energy Commission–Prof. A. Pazy joint foundation, ID126-2020. S.H. and R.A. acknowledge funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 889546 as well as from the Spanish MICINN (project grant PID2019-104739GB-100/AEI/10.13039/501100011033). R.A. also support the funding from the European Union H2020 program Graphene Flagship CORE3 (881603).Peer reviewe

Shelling with MoS2: Functional CuS@MoS2 hybrids as electrocatalysts for the oxygen reduction and hydrogen evolution reactions

The development of noble-metal free electrocatalysts is of high importance for clean energy conversion applications. MoS2 has been considered as a promising low-cost catalyst for the hydrogen evolution reaction (HER), however its activity is limited by poor conductivity and low abundance of active sites. Moreover, its suitability as an effective catalyst for other reactions, in particular the oxygen reduction reaction (ORR), was hardly explored to date. Herein, we show hybrid nanostructures of shelled CuS particles with MoS2 layers, which produces several outcomes: The MoS2 shell is strained and defective, and charge transfer from the core to MoS2 occurs, enabling activation of the basal plane of MoS2. Changing the feed ratio of the precursors led to control over morphology, such that the wrapping of the cores with the shell was continuously varied and characterized. We found an optimal hybrid structure, which provided high electrochemical active surface area and fast charge transfer kinetics, leading to improved activity not only towards HER (overpotential of 225 mV at 10 mA cm−2), but also for the sluggish ORR (onset potential 0.87 V vs RHE).This research was supported by the United States – Israel Binational Science Foundation (BSF), Jerusalem, Israel and the United States National Science Foundation (NSF) grant 2017642, and partly from the Israeli Atomic Energy Commission–Prof. A. Pazy joint foundation. The HRSTEM and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. S.H. acknowledges funding by German Research Foundation (HE 7675/1-1). R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the MICINN through project grants MAT2016-79776-P (AEI/FEDER, UE) and PID2019-104739GB-I00/AEI/10.13039/501100011033, as well as from the European Union H2020 programs “Graphene Flagship” (881603) and “ESTEEM3” (823717).Peer reviewe