Metal oxides are attracting increased attention as electrocatalysts owingto their affordability, tunability, and reactivity. However, these materials can undergosignificant chemical changes under reaction conditions, presenting challenges forcharacterization and optimization. Herein, we combine experimental and computationalmethods to demonstrate that bulk hydrogen intercalation governs the activity oftungsten trioxide (WO3) toward the hydrogen evolution reaction (HER). In contrast tothe focus on surface processes in heterogeneous catalysis, we demonstrate that bulkoxide modification is responsible for experimental HER activity. Density functionaltheory (DFT) calculations reveal that intercalation enables the HER by altering theacid-base character of surface sites and preventing site blocking by hydration. First-principles microkinetic modeling supports that the experimental HER rates can only beexplained by intercalated HxWO3, whereas nonintercalated WO3does not catalyze the HER. Overall, this work underscores thecritical influence of hydrogen intercalation on aqueous cathodic electrocatalysis at metal oxides.
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