Operando laboratory X-ray imaging of silver-based gas diffusion electrodes during oxygen reduction reaction in highly alkaline media
Operando laboratory X-ray radiographies were carried out for imaging of two diﬀerent silver-based gas diﬀusion electrodes containing an electroconductive Ni mesh structure, one gas diﬀusion electrode composed of 95 wt.% Ag and 5 wt.% polytetraﬂuoroethylene and one composed of 97 wt.% Ag and 3 wt.% polytetraﬂuoroethylene, under diﬀerent operating parameters. Thereby, correlations of their electrochemical behavior and the transport of the 30 wt.% NaOH electrolyte through the gas diﬀusion electrodes were revealed. The work was divided into two parts. In the ﬁrst step, the microstructure of the gas diﬀusion electrodes was analyzed ex situ by a combination of focused ion beam technology and synchrotron as well as laboratory X-ray tomography and radiography. In the second step, operando laboratory X-ray radiographies were performed during chronoamperometric measurements at diﬀerent potentials. The combination of the ex situ microstructural analyses and the operando measurements reveals the impact of the microstructure on the electrolyte transport through the gas diﬀusion electrodes. Hence, an impact of the Ni mesh structure within the gas diﬀusion electrode on the droplet formation could be shown. Moreover, it could be observed that increasing overpotentials cause increasing electrolyte transport velocities and faster droplet formation due to electrowetting. In general, higher electrolyte transport velocities were found for the gas diﬀusion electrode with 97 wt.% Ag in contrast to that with 95 wt.% Ag.