Understanding electrocatalyst dynamics under realistic operating conditions requires experimental platforms capable of integrating stable electrochemical environments with high-sensitivity synchrotron techniques. Soft X-ray absorption spectroscopy (soft-XAS) provides unique insight into the electronic structure of both transition metals and light elements, but its implementation under electrochemical conditions is typically limited by gas bubble formation, electrolyte instabilities, and stringent vacuum compatibility requirements.

Building on the design principles of the operando electrochemical cell currently in use at the BACH beamline (Elettra Sincrotrone Trieste) [1], we have developed a next-generation, UHV-compatible high-flow electrochemical cell (EC-cell) specifically engineered for operando soft-XAS under conditions that closely resemble real electrochemical operation. Developed in collaboration with Sectris (https://sectris.tech/), the EC-cell incorporates optimized electrolyte-flow geometry, a custom 3D-printed internal core, and an external protective capsule. The device supports high current densities (hundreds of mA cm^-2) and high electrolyte fluxes (~mL s^-1), efficiently mitigating gas-bubble accumulation and ensuring stable electrochemical performance during soft-XAS acquisition. This EC-cell will be implemented as a new permanent setup at the BACH operando end-station, significantly expanding its capabilities for energy-materials research.

The cell was validated through operando soft-XAS of NiOOH under oxygen evolution reaction (OER) conditions. Stable spectra were obtained up to 100 mA cm^-2 with consistent electrochemical behavior and well-resolved Ni L-edge features. No Ni species above the established Ni²⁺/³⁺ redox couple were observed, however, the transient formation of Ni⁴⁺ species cannot be ruled out. A new O K-edge spectral feature emerging at high catalytic currents was attributed to the accumulation of molecular oxygen near the electrode-electrolyte interface, providing direct spectroscopic evidence of local O₂ evolution under operando conditions. Density functional theory (DFT) simulations of the Ni L-edge and O K-edge spectra support these assignments.

Beyond these initial demonstrations, the high-flow EC-cell enables new opportunities for time-resolved spectro-electrochemical measurements, which colud clarify whether short-lived Ni⁴⁺ species form during OER. Inspired by the sub-millisecond electrochemically induced Raman (EIR) approach of D’Amario et al. [2], we aim to synchronize pulsed electrochemical excitation with chopped soft X-ray beam, enabling direct detection of short-lived intermediates involved in electrocatalytic pathways. This approach will further expand mechanistic insights into electrochemical energy-conversion reactions.