μautolab 3

Electrochemical workstation (μAutolab III, Metrohm, Herisau, Switzerland) and its supporting software NOVA; field emission scanning electron microscope (SU-8010, Hitachi, Tokyo, Japan); FTIR spectroscopy (characterization using (Nicolet iS 50, Thermo Fisher, Shanghai, China); 120 kV transmission electron microscope (HT-7700, Hitachi).

Cyclic voltammetry⁵¹ experiments were performed with a three-electrode cell. A saturated calomel electrode (SCE) was used as reference, a steady glassy carbon (GC) electrode of diameter 3 mm was selected as working electrode and a platinum wire as counter-electrode. All cyclic voltammograms were recorded at room temperature with a μ-autolab III from Metrohm using Nova software with a scan rate of 2 V/s. MeCN and MeOH were used in HPLC grade (Carlo Erba). For all experiments we used a 0.1 M nBu₄NBF₄ in MeCN (32.9 mg/μL stock solution). 1 mM FeCl₃ solutions were prepared with 50 μL of 20 mM FeCl₃ solution in milliQ water and 950 μL of MeCN. Then, portions of 10 μL (0.2 eq.) of 20 mM stock solution of Lip-1 or analogues (solubilised in MeCN or MeOH) were added until 1.0 eq. was reached. Above 1.0 eq., 50 μL (1.0 eq.) of 20 mM stock solution of the analogues were added. After each addition, the solution was stirred for a few seconds and voltammograms were recorded.

IES technique was used to determine the ionic conductivity of the terracotta clay membranes by using the μAutoLab III with a frequency response analyser FRA2 (Metrohm, The Netherlands). The range of frequency selected to perform the measurements was the following: 100 kHz to 10 mHz, at AC amplitude of 10 mV in a two electrodes configuration where the reference electrode was short-circuited to the counter electrode. The conductivity of each sample was determined by extracting the bulk resistance (R_b) by the intersection of the semicircle with the Z’ axis in the Nyquist plot [[26] , [27] , [28] ]. Then, the ionic conductivity of the different membranes was calculated by using the following equation: $\sigma =\frac{\text{L}}{A\times R_b}$ Where σ is the ionic conductivity (S.cm⁻¹), L (cm) the thickness of the membrane, A (cm²) the contact area between the electrodes and the ceramic membrane and R_b (Ω) is extracted from the Nyquist plot, as previously commented [28 ].
The IES measurements were performed by using the same MFC set-up that was employed for running the experimental tests but using buffer pH 9 as electrolyte and two thin pieces of carbon veil as electrodes. According to this configuration, both the R_b and the conductivity are mainly related to each type of membrane analysed. These parameters have been reported to be crucial for well-performing MFCs [28 ].