Combining ToF-SIMS and multivariate analysis to resolve active sites on Ni-based HER catalystsFinšgar, Matjaž (Avtor) Varda, Katja Andrina (Avtor) Kozlica, Dževad (Avtor) Huš, Matej (Avtor) Martins, Milena (Avtor) Strmčnik, Dušan (Avtor) HER active sitesmultivariate statistical analysisnickel catalystsToF-SIMSUnambiguous identification of active sites in heterogeneous catalysis remains a major challenge, particularly formaterials with ultrathin, chemically mixed surface layers. Here, we demonstrate a generalizable approach that combinestime-of-flight secondary ion mass spectrometry (ToF-SIMS) with multivariate statistical analysis (principal componentanalysis [PCA] and multivariate curve resolution [MCR]) to resolve catalytically relevant motifs at the nanoscale. Using Nielectrodes as a model system, PCA distinguished hydroxide-enriched domains from oxide- and metal-rich regions, whileMCR decomposed depth profiles and 3D images into hydroxide, oxide, and metallic layers with nanometer resolution.A unique secondary-ion fragment, NiO3 H 3− (m/z 108.94), emerged as a marker of hydroxide-rich environments andcorrelated with hydrogen evolution reaction (HER) activity across a series of Ni electrodes. Complementary densityfunctional theory (DFT) calculations revealed that Ni(OH)2 clusters adjacent to metallic Ni offer the most favorable waterdissociation energetics, establishing the structural origin of the marker. While illustrated here for Ni-based HER, thisworkflow provides a broadly applicable framework to isolate and rank near-surface patterns that govern catalytic activity,thereby extending ToF-SIMS from a qualitative probe to a predictive tool for active site identification.20262026-07-08 12:11:52Neznano30902UDK: 54ISSN pri članku: 1521-3773DOI: 10.1002%2Fanie.202519929COBISS_ID: 265392899sl© 2026 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.