Linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry measurements were performed with an Autolab PGSTAT302 potentiostat/galvanostat, in a three-electrode configuration cell. The cell consisted of a Pt wire as the counter electrode, an Ag/AgCl (3 M KCl) electrode as the reference electrode, and the porphyrin coating on fluorine-doped tin oxide (FTO) coated glass as the working electrode. A 1 M potassium hydroxide (Sigma Aldrich) solution at pH 13.6 was used as the alkaline electrolyte. Alternatively, a 0.5 M sodium sulphate (Sigma Aldrich) solution at pH 6.08 was used as the electrolyte for measurements under acidic conditions. All the potentials were referenced to the Reversible Hydrogen Electrode (RHE) using the Nernst equation: VRHE = VAg/AgCl + V0Ag/AgCl + 0.0591 × pH.
The oxygen evolution at the surface of the oCVD thin films was determined by gas chromatography measurements using a sealed cell coupled to an Agilent Micro-GC gas chromatograph, during a chronoamperometric measurement at 1.63 V vs. RHE. The faradaic efficiency (FE) was estimated through the relationship: FE (%) = O2(exp)/O2(theo), where O2(exp) is the amount of evolved O2 in mol, monitored every 5 min, and O2(theo) is the theoretical O2 evolution calculated with Faraday's law: n (mol cm−2) = jO2t/nF, where jO2 is the current density recorded by chronoamperometry measurement, t is the time in seconds, n is the number of electrons transferred in the reaction and F is the Faraday constant, 96 485.33 C mol−1.
The oxygen evolution at the surface of the oCVD thin films was determined by gas chromatography measurements using a sealed cell coupled to an Agilent Micro-GC gas chromatograph, during a chronoamperometric measurement at 1.63 V vs. RHE. The faradaic efficiency (FE) was estimated through the relationship: FE (%) = O2(exp)/O2(theo), where O2(exp) is the amount of evolved O2 in mol, monitored every 5 min, and O2(theo) is the theoretical O2 evolution calculated with Faraday's law: n (mol cm−2) = jO2t/nF, where jO2 is the current density recorded by chronoamperometry measurement, t is the time in seconds, n is the number of electrons transferred in the reaction and F is the Faraday constant, 96 485.33 C mol−1.
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