This paper reports the performance of hydrogen evolution reaction (HER) electrocatalysts based on Pt thin film electrodes that are encapsulated by silicon oxide (SiO x ) nanomembranes. This membrane-coated electrocatalyst (MCEC) architecture offers a promising approach to enhancing electrocatalyst stability while incorporating advanced catalytic functionalities such as poison resistance and tunable reaction selectivity. Herein, a roomtemperature ultraviolet (UV) ozone synthesis process was used to systematically control the thickness of SiO x overlayers with nanoscale precision and evaluate their influence on the electrochemically active surface area (ECSA) and HER performance of the underlying Pt thin films. Through detailed characterization of the physical and electrochemical properties of the SiO x -encapsulated electrodes, it is shown that proton and H 2 transport occur primarily through the SiO x coating such that the HER takes place at the buried Pt|SiO x interface. Increasing the thickness of the SiO x overlayers results in monotonic increases in the overpotential losses of the MCEC electrodes. These overpotential losses were fit using a one-dimensional diffusion model, from which the H + and H 2 permeabilities through SiO x were obtained. Importantly, the SiO x nanomembranes were found to exhibit high selectivity for proton and H 2 transport in comparison to Cu 2+ , a model HER poison. Leveraging this property, we show that SiO x encapsulation can enable copperresistant operation of Pt HER electrocatalysts. It is expected that a more complete understanding of the structure−property− performance relationships of the SiO x overlayers will enable the design of stable MCECs capable of multifunctional catalysis with minimal loss in efficiency from concentration overpotential losses associated with mass transport through SiO x .

Alkyne-functional polymers synthesized by ATRP exhibit bimodal molecular weight distributions indicating the occurrence of some undesirable side reaction. By modeling the molecular weight distributions obtained under various reaction conditions, we show that the side reaction is alkyne-alkyne (i.e., Glaser) coupling. Glaser coupling accounts for as much as 20% of the polymer produced, significantly compromising the polymer functionality and undermining the success of subsequent click reactions in which they are used. Glaser coupling does not occur during ATRP but during postpolymerization workup upon first exposure to air. Two strategies are reported that effectively eliminate these coupling reactions without the need for a protecting group for the alkyne-functional initiator: (1) maintaining low temperature post-ATRP upon exposure to air followed by immediate removal of copper catalyst; (2) adding excess reducing agents post-ATRP which prevent the oxidation of Cu(I) catalyst required by the Glaser coupling mechanism. Post-ATRP Glaser coupling was also influenced by the ATRP synthesis ligand used. The order of ligand activity for catalyzing Glaser coupling was: linear bidentate > tridentate > tetradentate. We find that Glaser coupling is not problematic in ARGET-ATRP of alkyne-terminated polymers because a reducing agent is present during polymerization, however the molecular weight distribution is broadened compared to ATRP due to the presence of oxygen. Glaser coupling can also occur for alkynes held under CuAAC reaction conditions but again can be eliminated by adding appropriate reducing agents.

Polymer properties are inherently multi-scale in nature, where delicate local interaction details play a key role in describing their global conformational behavior.In this context, deriving coarse-grained (CG) multi-scale models for polymeric liquids is a non-trivial task. Further complexities arise when dealing with copolymer systems with varying microscopic sequences, especially when they are of an amphiphilic nature. In this work, we derive a segment-based generic CG model for amphiphilic copolymers consisting of repeat units of hydrophobic (methylene) and hydrophilic (ethylene oxide) monomers. The system is a simulation analogue of polyacetal copolymers [Samanta et al., Macromolecules 49, 1858]. The CG model is found to be transferable over a wide range of copolymer sequences and also to be consistent with existing experimental data.

ABSTRACT:1 H NMR and SEC analyses are used to investigate the overall efficiency of Copper Catalyzed Azide Alkyne Cycloaddition (CuAAC) "click" coupling reactions between alkyneand azide-terminated polymers using polystyrene as a model. Quantitative convolution modeling of the entire molecular weight distribution is applied to characterize the outcomes of the functional polymer synthesis reactions (i.e., by atom transfer radical polymerization), as well as the CuAAC coupling reaction. Incomplete functionality of the azide-terminated polystyrene ($92%) proves to be the largest factor compromising the efficacy of the CuAAC coupling reaction and is attributed primarily to the loss of terminal bromide functionality during its synthesis. The efficiency of the S N 2 reaction converting bromide to azide was found to be about 99%. After taking into account the influence of non-functional polymer, we find that, under the reaction conditions used, the efficiency of the CuAAC coupling reaction determined from both techniques is about 94%. These inefficiencies compromise the fidelity and potential utility of CuAAC coupling reactions for the synthesis of hierarchically structured polymers. While CuAAC efficiency is expected to depend on the specific reaction conditions used, the framework described for determining reaction efficiency does provide a means for ultimately optimizing the reaction conditions for CuAAC coupling reactions.