Electrodeposition of oxy-carbide of CrMnFeCoNi and measurement of catalytic activity on oxygen evolution reaction

The excellent catalytic activity of oxygen evolution reaction (OER) has been demonstrated for many high-entropy compounds. Here, several amorphous coatings of oxy-carbide of isolated metals (Cr, Mn, Fe, Co, or Ni) or mixed metals were electrodeposited in organic solvent-based chlorides. The oxy-carbide coating of mixed metals indicated the presence of Cr, Mn, Fe, Co, and Ni. The electrodeposition mechanism was discussed, and the OER catalytic activity was investigated. Composition analysis confirmed the existence of carbon and oxygen in the coatings, originating from the water molecules hydrated with metal ions and the organic solvent. Upon these, a novel one-step electrodeposition process was established without solution pretreatment of deaeration and dehydration. The oxy-carbide coating of mixed metals showed high catalytic activity for OER in the alkaline solution, achieving an overpotential of 263 mV corresponding to a current density of 10 mA cm-2. A long stability at the current density of 10 mA cm-2 was obtained for 50 h, with a stable overpotential and minor surface dissolution. The coating of the oxy-carbide of Ni also showed comparably high catalytic activity for the OER. The DFT-calculated overpotential was similar to the experimental results. In particular, a specific Cr site showed high catalytic activity. Finally, an indicator of the unsaturated oxidation number of metal atoms was proposed to depict the relationship between the overpotential of the active site and the binding state.