Metal oxides are attracting increased attention as electrocatalysts owing to their affordability, tunability, and reactivity. However, these materials can undergo significant chemical changes under reaction conditions, presenting challenges for characterization and optimization. Herein, we combine experimental and computational methods to demonstrate that bulk hydrogen intercalation governs the activity of tungsten trioxide (WO 3 ) toward the hydrogen evolution reaction (HER). In contrast to the focus on surface processes in heterogeneous catalysis, we demonstrate that bulk oxide modification is responsible for experimental HER activity. Density functional theory (DFT) calculations reveal that intercalation enables the HER by altering the acid−base character of surface sites and preventing site blocking by hydration. Firstprinciples microkinetic modeling supports that the experimental HER rates can only be explained by intercalated H x WO 3 , whereas nonintercalated WO 3 does not catalyze the HER. Overall, this work underscores the critical influence of hydrogen intercalation on aqueous cathodic electrocatalysis at metal oxides.

The ability to predict intercalation energetics from first principles is attractive for identifying candidate materials for energy storage, chemical sensing, and catalysis. In this work, we introduce a computational framework that can be used to predict the thermodynamics of hydrogen intercalation in tungsten trioxide (WO 3 ). Specifically, using density functional theory (DFT), we investigated intercalation energetics as a function of adsorption site and hydrogen stoichiometry. Site-specific acid−base properties determined using DFT were used to develop linear structure screening models that informed a kernel ridge energy prediction model. These regressions provided a series of hydrogen binding energy predictions across stoichiometries ranging from WO 3 to H 0.625 WO 3 , which were then converted to equilibrium potentials for hydrogen intercalation. Experimental validation using cyclic voltammetry measurements yielded good agreement with the predicted intercalation potentials. This methodology enables fast exploration of a large geometric configuration space and reveals an intuitive physical relationship between acidity, basicity, and the thermodynamics of hydrogen intercalation. Furthermore, the combination of theoretical and experimental results suggests H 0.500 WO 3 as a maximum stable stoichiometry for the bronzes that arises from competition with hydrogen evolution rather than the inability of WO 3 to accommodate additional hydrogen. Our experimental results further indicate hydrogen insertion in WO 3 is highly irreversible for low H-stoichiometries, which we propose to be a consequence of the semiconductor-to-metal transition that occurs upon initial H-intercalation. Overall, the agreement between theory and experiment suggests that local acid−base characteristics govern hydrogen intercalation in tungsten trioxide, and this insight can aid the accelerated discovery of redox-active metal oxides for catalytic hydrogenations.

Solid-state, mechanochemical polymer processing techniques are explored as an effective and sustainable solution to appearance and performance issues commonly associated with recycled plastic products. Post-consumer high-density polyethylene (HDPE) from milk jugs is processed via conventional twin screw extrusion (TSE), solid-state shear pulverization (SSSP), and solidstate/melt extrusion (SSME), and compared to the as-received and virgin forms regarding output attributes and mechanical properties, as well as morphology. Solid-state processing methods, particularly SSME with a harsh screw configuration, produce samples with consistent appearance and melt flow characteristics. Tensile ductility/toughness and impact toughness are enhanced by up to 11-fold as compared to the as-received sample, to a level near and above those of an equivalent virgin HDPE. Calorimetry, optical microscopy, X-ray scattering, and rheology characterization reveal that the mechanical improvements result from a favorable combination of physical and molecular changes in rHDPE, such as impurity size reduction, spherulite size enlargement, and chain branching.

In situ optical microscopy measurements show that thermochemical H-spillover and electrochemical H-intercalation in tungsten oxide proceed by a congruent mechanism at room temperature in the presence of an acidic electrolyte.