Quasi-1D Oxides as Electrocatalysts for Water-Splitting: Case Study of Sr₉M₂Mn₅O₂₁ (M = Co, Ni, Cu, Zn)

We have demonstrated that multimetal oxides with a quasi-1D structure can be effective electrocatalysts for water electrolysis. Four materials have been systematically investigated, namely, Sr₉Co₂Mn₅O₂₁, Sr₉Ni₂Mn₅O₂₁, Sr₉Cu₂Mn₅O₂₁, and Sr₉Zn₂Mn₅O₂₁, comprising 1D chains of face-sharing MnO₆ octahedra and MO₆ trigonal prisms (M = Co, Ni, Cu or Zn), which are held together by strontium ions located between the chains. These materials show a consistent trend in electrocatalytic properties for both half-reactions of water-splitting, i.e., oxygen evolution and hydrogen evolution reactions (OER and HER). In particular, Sr₉Ni₂Mn₅O₂₁ has an outstanding performance for OER, with an overpotential of 0.37 V, which is lower than those of many 3D and 2D oxides, and rivals the activity of noble metal catalysts, such as RuO₂. This is important given that the OER is considered the bottleneck of the water-slitting process. Chronopotentiometry studies, combined with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction experiments pre- and post-reaction, indicate that Sr₉Ni₂Mn₅O₂₁ is highly stable and retains its structural integrity upon electrocatalytic reactions. This study highlights the potential of quasi-1D oxides as active electrocatalysts for water-splitting.