Aim of the MANGAN project was the evaluation of various manganese based materials towards their OER activity and stability and the compilation of the results in a common database. By comprising a large set of data from different samples, it was intended to identify a potentially underlying structure-function relationship and to extend the fundamental understanding of Mn in various formulations for the purpose as a catalyst for water splitting. To facilitate the comparability amongst the individual samples, a measurements protocol was developed, serving as basis for the electrochemical characterization.

MANGAN standard measurements protocol:

For the standard procedure, a rotating disk electrode (RDE) with a glassy-carbon working‑electrode‑support (Æ 4mm) in PEEK sheath (Ø 10 mm), a Hg/HgO reference electrode and a Pt coil as counter electrode. Electrochemical measurements were run in 1M KOH (pH 14) as electrolyte using a customized 150 mL PEEK beaker. To remove any residuals on the working electrodes and to obtain a smooth surface, prior to use the electrodes are polished with polishing paste (Al₂O₃ slurry; 1.0 µm and 0.05 µm) on a wet polishing cloth for 3-5 minutes, and rinsed thoroughly with water. Before drop-coating of catalyst, electrodes are ultrasonicated in absolute ethanol for 5 minutes, rinsed thoroughly with water, ultrasonicated in millipore water for 5 minutes, rinsed thoroughly with water and let to dry in argon stream. The catalyst films were prepared as inks from powder samples, using the polymer Nafion™ as a binder and drop coated on the electrode. The standard ink typically consist of 49% water, 49% ethanol and 2% Nafion solution (5 wt.%) and 5 mg/mL of catalyst. A Metrohm potentiostat with the Metrohm Autolab software NOVA was used to conduct the electrochemical sample characterization. Identical setups distributed amongst the project partners together with a step-by-step procedure of measurements and sample treatment. To compare the performance of the samples towards OER a set of key performance indicators (KPI) was defined. These are:

• Activity indicators, recording the potential (vs. RHE) to reach 2, 5, and 10 mAcm^-2:
  • E_2mA/cm-_², E_5mA/cm-_², E_10mA/cm-_²
• And/or activity indicators, recording the mass activity at 1.6, 1.7, and 1.8 V (vs. RHE) in mAmg^‑1:
  • i_mass,1.6V, i_mass,1.7V, i_mass,1.8V
• Chronoamperometric stability indicators, maintaining a constant current density of 10mAcm^‑2 and recording the required potential at 0, 0.5, and 2h:
  • E_t=0h, E_t=0.5h, E_t=2h
• And/or chronopotentiometric stability indicators, maintaining a constant (iR-corrected) potential and recording the mass activity at 0, 0.5, and 2h:
  • j_t=0h, j_t=0.5h, j_t=2h
• An optional second set of activity indicators, identical to the procedure to obtain the initial activity:
  • E’_2mA/cm-_², E’_5mA/cm-_², E’_10mA/cm-_², i'_mass,1.6V, i'_mass,1.7V, i'_mass,1.8V

(Standard scan rates were 5 mV/s)

The results presented in this database were collected in the course of the project by the individual project partners. In order to allow for experimental freedom, the project partners were not rigorously restricted to the protocol, especially in the choice of the electrode support. Deviations from the protocol are specified in the respective database entries. To generate a comprehensive overview of the catalytic activity and stability of different materials also samples with a low performance are listed in the database.