Quantifying bubble dynamics via fiber optic sensor for <i>in situ</i> electrocatalytic evaluation

The hydrogen evolution reaction (HER) in electrochemical water splitting is crucial for green hydrogen production, yet its efficiency is limited by bubble dynamics at the electrode surface. Accumulated bubbles can block active sites, hinder mass transport, and increase local resistance, causing energy loss. Thus, precise bubble monitoring is crucial for understanding performance limitations and optimizing catalyst design. Conventional bubble monitoring techniques, such as optical microscopy, high-speed imaging, and electrochemical impedance, are constrained by real-time accuracy, complex post-processing, or signal interference at high current densities. Here, we present an in-situ fiber optic sensing system that enables precise, real-time monitoring of bubble dynamics during HER. Unlike traditional methods, this system leverages the sensitivity and real-time capability of fiber optic sensors to quantify key parameters, such as growth rate, detachment rate, intake/output ratio, and detaching size. Its reliability and adaptability were validated using two different Pt/C-loaded carbon paper catalysts with distinct catalytic properties. Notably, the system also achieves a bubble detection limit of 79 μm, which meets the spatial resolution requirements for monitoring bubble dynamics relevant to electrocatalytic activity in HER. This sensing platform establishes a practical framework for connecting interfacial gas evolution to electrochemical performance, offering valuable insight for optimizing HER efficiency through catalyst design.