Electrodeposited Transition Metal Dichalcogenides for Use in Hydrogen Evolution Electrocatalysts

Hydrogen is a promising alternative to gasoline due to its higher energy density and ability to burn cleanly only producing H2O as a by-product. Electrolytic water splitting is an effective technique for generating molecular hydrogen. However, for hydrogen to be a viable alternative energy source to be produced from water electrolysis, affordable and durable electrocatalysts need to be developed to replace platinum. Transition metal dichalcogenides (TMDs) are a promising alternative since they are abundant, inexpensive, and have a tunable structure. There are various ways to produce TMD films including chemical and mechanical exfoliation, chemical vapor deposition (CVD), and electrodeposition. Exfoliation and CVD techniques often require a transfer of TMDs from the growth substrate to an electrode, which introduces impurities and possible defects to the film. Electrodeposition, however, provides a way to produce TMDs directly onto the electrode with excellent surface coverage. This work uses electrodeposition to produce TMD and TMD bilayer electrodes using sequential electrodeposition for electrocatalytic hydrogen evolution reaction (HER). The results presented include cost-effective deposition techniques along with enhanced proton reduction activity for the sequentially deposited bilayer TMD structure consisting of MoS2 and MoSe2, which suggests the electron transfer kinetics from the conductive glass substrate to the top-layer is enhanced with a MoS2 layer. Furthermore, the bilayer structures synthesized by sequential deposition are characterized via XPS, XPS depth-profiling, and SEM-EDS for enhanced understanding of the fabricated structure.</jats:p

Quantitative MALDI-MS and Imaging of Fungicide Pyrimethanil in Strawberries with 2‑Nitrophloroglucinol as an Effective Matrix

This work explores the use of 2-nitrophloroglucinol (2-NPG) as a matrix for quantitative analysis of the fungicide Pyrimethanil (PYM) in strawberries using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and imaging. 2-NPG was selected for PYM analysis for optimum sensitivity and precision compared to common matrices α-cyano-4-hydroxylcinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB). PYM-sprayed strawberries were frozen 0, 1, 3, and 4 days after treatment and sectioned for MALDI imaging. The remaining part of each strawberry was processed using quick easy cheap effective rugged and safe (QuEChERS) extraction and analyzed by MALDI-MS and ultraperformance liquid chromatography multireaction-monitoring (UPLC-MRM). MALDI-MS showed comparable performance to UPLC-MRM in calibration, LOD/LOQ, matrix effect, and recovery, with the benefit of fast analysis. The MALDI imaging results demonstrated that PYM progressively penetrated the interior of the strawberry over time and the PYM concentration on tissue measured by MALDI imaging correlated linearly with MALDI-MS and UPLC-MRM measurements and accounts for 79% MALDI-MS and 85% UPLC-MRM values on average. Additionally, quartz crystal microbalance (QCM) was introduced as a new approach to determine strawberry tissue mass per area for MALDI imaging absolute quantitation with sensitive, direct, and localized measurements. This work demonstrates the first example of absolute quantitative MALDI imaging of pesticides in a heterogeneous plant tissue. The novel use of the 2-NPG matrix in quantitative MALDI-MS and imaging could be applied to other analytes, and the new QCM tissue mass per area method is potentially useful for quantitative MALDI imaging of heterogeneous tissues in general