Fig. 4: OER electrochemical performance.

Automated ultrasonic spray coating has been used for the multiscale electrode preparation ranging from 0.196 cm² glassy carbon RDE to 1 cm² nickel-fiber DEC to finally 5 cm² AEM water electrolyzer (a). Scheme of electrochemical configuration (b) RDE measurements on GC at RT and 2500 rpm in 1 M KOH after 30 activation cycles (50 mV s⁻¹) and the extended galvanostatic activation protocol (c, d). Slow scan rate CVs (5 mV s⁻¹) of the catalyst after the activation process(c). Polarization curves obtained by galvanostatic steps up to 15 mA cm⁻² (d). The plotted potential is corrected with the uncompensated electrolyte resistance (R_u) obtained from impedance measurements at each step. DEC measurements on Ni-fiber substrate at RT and 65 °C in 1 M KOH after 30 activation cycles (50 mV s⁻¹) (e, f). Slow scan rate CVs (5 mV s⁻¹) of the catalyst after the activation process (e). Polarization curves obtained by galvanostatic steps up to 500 mA cm⁻² for the RT-NiFe-LDH with three repetitions for each at 25 °C and 65 °C in 1 M KOH. The plotted potential is corrected with R_u obtained from impedance measurements at each step. Polarization curve, high frequency resistance (HFR), and HFR-corrected polarization curve obtained in the AEMWE configuration by galvanostatic steps up to 3000 mA cm⁻² after conditioning and break-in at 70 °C in 1 M KOH (g). Polarization curves are always plotted as the mean value from three independent repetitions for each measurement, whereas error bars show the respective standard deviation.