Localized probing of real-time hydrogen-materials interaction: An in-situ electrochemical approach based on secondary ion mass spectrometry

Thin films play a crucial role in hydrogen-related technologies like hydrogen storage, protective coatings, embrittlement studies, etc. However, direct high spatial resolution observation of hydrogen distribution in such systems in real-time remains a significant experimental challenge. In this study, we present a novel in-situ electrochemical hydrogen charging set-up, the "HyBack" cell, integrated within a focused ion beam-scanning electron microscope-secondary ion mass spectrometer (FIB-SEM-SIMS) for real-time visualization of hydrogen uptake and hydride formation in titanium (Ti) thin films. The custom-designed cell allows real-time electrochemical hydrogen insertion under vacuum conditions while enabling high-resolution SIMS imaging. Backscattered electron imaging provided subsurface contrast, enabling direct assessment of whether the substrate microstructure influenced hydride nucleation in the Ti film. In-situ 2D SIMS imaging revealed spatial and temporal evolution of hydrogen distribution, hydride phase nucleation and growth. While the FIB-SEM-SIMS platform is capable of nanoscale lateral resolution for hydrogen SIMS imaging under optimized conditions, the present in-situ electrochemical experiments demonstrate temporal evolution of hydrogen distribution with an effective lateral resolution of the order of 100 nm. Complementary imaging by laser scanning confocal microscopy (LSCM) under ambient conditions confirmed the transformation dynamics. The results supported kinetic modelling and the approximate estimation of effective transformation parameters and average hydrogen concentrations in the Ti thin film using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) framework. Comparative analysis with deuterium was performed to overcome hydrogen contribution from the high vacuum environment during SIMS analysis and time resolved LSCM images were used to demonstrate isotopic effects on hydride growth mechanisms. This integrated approach bridges a critical methodological gap in hydrogen-materials research and provides a robust tool for studying hydrogen behaviour in thin films with high spatial and temporal precision. • Development of a novel vacuum-compatible cell for in-situ backside hydrogen charging and SIMS imaging. • Time resolved 2D SIMS imaging of hydrogen distribution and hydride growth in Ti thin films. • Operando confocal microscopy captures hydride growth under ambient conditions. • Experimental observations combined with JMAK modelling provides growth kinetics and hydrogen concentration estimates.